no. 30. gestational diabetes

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VOL. 98, NO. 3, SEPTEMBER 2001 ACOG Practice Bulletin No. 30 Gestational Diabetes 525

ACOG

PRACTICE

BULLETINCLINICALMANAGEMENTGUIDELINES FOR

OBSTETRICIANGYNECOLOGISTS

NUMBER30, SEPTEMBER2001

(Replaces Technical Bulletin Number 200, December 1994)

This Practice Bulletin was

developed by the ACOG Com-

mittee on Practice Bulletins

Obstetrics with the assistance

of Donald R. Coustan, MD. The

information is designed to aid

practitioners in making deci-

sions about appropriate obstet-

ric and gynecologic care. These

guidelines should not be con-

strued as dictating an exclusive

course of treatment or proce-

dure. Variations in practice may

be warranted based on the

needs of the individual patient,

resources, and limitations

unique to the institution or type

of practice.

Gestational DiabetesGestational diabetes mellitus (GDM) is one of the most common clinical issuesfacing obstetricians and their patients. A lack of data from well-designed stud-

ies has contributed to the controversy surrounding the diagnosis and manage-

ment of this condition. The purpose of this document is to provide a brief

overview of our understanding of GDM and provide management guidelines

that have been validated by appropriately conducted clinical research. When

outcomes-based research is not available, expert opinion is provided to aid the

practitioner.

BackgroundDefinition and PrevalenceDiabetes is classified as type 1 or type 2 according to whether the patient

requires insulin injections to avoid ketoacidosis. Gestational diabetes mellitus

has been characterized as carbohydrate intolerance that begins or is first recog-

nized during pregnancy. The prevalence of GDM varies in direct proportion to

the prevalence of type-2 diabetes in a given population or ethnic group.

Reported prevalence in the United States ranges from 1% to 14%, with 25%

being the most common figure (1).

Maternal and Fetal Complications

Women with GDM are more likely to develop hypertensive disorders than

women without GDM (2). Some of this additional risk may be related to theunderlying risk factors for GDM (eg, increased maternal age and obesity). The

diagnosis of GDM may prompt health care providers to intervene more readily

for perceived problems (3). In women without GDM, there is a significant asso-

ciation between increasing carbohydrate intolerance and both preeclampsia and

cesarean delivery (4). Women with GDM in Korea have a higher incidence of

preeclampsia and primary cesarean delivery, yet only 10% of the women are

obese (5). Whether the relationship with GDM is causal or not, clinicians


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526 ACOG Practice Bulletin No. 30 Gestational Diabetes OBSTETRICS & GYNECOLOGY

should be aware of these risks. In addition, women with

GDM have an increased risk of developing diabetes later

in life.

The offspring of women with GDM are prone to

such adverse events as macrosomia with its potential

complications and hyperbilirubinemia. Infants of women

with GDM are at increased risk for operative delivery,

shoulder dystocia, and birth trauma. Because the risk fac-tors for GDM (particularly obesity) are independent risk

factors for fetal macrosomia, the role of maternal hyper-

glycemia has been widely debated. Although controlling

for maternal obesity eliminated the apparent relationship

between hyperglycemia and macrosomia in some studies

(6, 7), these results may have been confounded because

the women with GDM were treated. The relationship

between GDM, fetal macrosomia, and other adverse

outcomes has been confirmed in cohort studies in which

maternal obesity and other potential confounders were

controlled (8, 9), in a study of Korean women among

whom only 10% were obese (5), and in another study of

women whose abnormal glucose tolerance tests (GTTs)

went clinically unrecognized (10). In women without

GDM, there is an independent relationship between GTT

levels and macrosomia (4, 11). When data were correct-

ed for maternal weight, age, parity, and race, the 12% risk

of macrosomia was independently attributable to GDM

(9). A number of studies also have linked maternal hyper-

glycemia with long-term obesity and diabetes in the

offspring (1214). Nevertheless, considerable contro-

versy remains regarding the exact relationship of these

complications to maternal hyperglycemia.

Controversy of Current ScreeningPractices and Treatment Benefits

At one time, screening for GDM consisted of taking the

patients history. In 1973, OSullivan and Mahan pro-

posed the 50-g, 1-hour laboratory screening test. This

test has become widely used94% of obstetric groups

surveyed reported universal testing (15)despite the

absence of data to demonstrate a benefit to the popula-

tion as a whole. However, as noted previously, maternal

hyperglycemia is related to at least some of the adverse

perinatal outcomes seen with GDM. Available evidence

does not support the concept that women with GDM

who do not have risk factors are of less concern than are

those who do (16).The use of traditional historic risk factors (family or

personal history of diabetes, previous adverse pregnancy

outcome, glycosuria, obesity) to identify GDM will miss

approximately half of women with GDM (17, 18). If the

risks of adverse outcomes are related to the presence or

absence of confounding risk factors, rather than the

GDM, then limited screening based on risk may be rea-

sonable. The U.S. Preventive Services Task Force has

concluded that although there is insufficient evidence to

recommend universal screening, screening high-risk

women may be beneficial (19).

Despite the lack of population-derived data support-

ing the benefit of making the diagnosis of GDM, clinical

recommendations often must be made without unassail-

able epidemiologic evidence. Older, admittedly flawed,studies suggested an increased perinatal mortality rate

among undiagnosed or untreated women with GDM (20,

21). More recent studies that did not demonstrate an

increase in perinatal mortality risk all included interven-

tions of diet or insulin, antepartum testing, or merely

making the diagnosis, which has been shown to be a

powerful intervention in and of itself (3). If the perinatal

mortality rate in undiagnosed and untreated GDM were

double the background rate, as suggested in earlier stud-

ies, and GDM occurs in 25% of the population, any

increase in overall perinatal loss attributable to discon-

tinuing screening programs would likely go unnoticed.

Another important issue to consider is the possibil-

ity that some patients diagnosed with GDM may have

preexisting type-2 diabetes, which can only be con-

firmed postpartum. One study found such patients to

have a perinatal mortality rate 6 times higher than those

with milder forms of GDM (22). Another study found

mothers with GDM who had infants with birth defects

were more likely to have high fasting glucose values,

suggesting the presence of undiagnosed preexisting dia-

betes (23).

For the population to benefit from the diagnosis of

GDM, there should be an effective treatment for the con-

dition. Although a number of comparative studies of var-ious treatments are available, there is little information

regarding the effectiveness of treatment versus no treat-

ment. In a pilot randomized trial comparing strict meta-

bolic control with routine obstetric care in 300 women

with GDM, there was no difference in the rate of macro-

somia or other pregnancy outcomes (24). However, even

the control subjects monitored their own glucose levels 1

day each week, and 10% were removed from the study

and treated for hyperglycemia.

The first consideration in selecting a therapy for

GDM is a determination of the treatment goals.

Although the degree, if any, of excess perinatal mortal-

ity associated with milder GDM has not been established,management plans typically include some type of fetal

surveillance. A second goal of treatment may be the

prevention of adverse pregnancy outcomes, such as

macrosomia and its attendant consequences of operative

delivery, shoulder dystocia, and birth trauma. Potential

treatments toward this goal include diet, exercise, and

insulin; oral agents also have been suggested. Safety,


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efficacy, and patient acceptance should be considered in

choosing a treatment.

The goal of treatment is to lower the likelihood of

macrosomia and its consequences; neonatal hypoglyce-

mia also may be reduced (25). Although the quality of

the information varies, evidence is available to confirm

these benefits. However, there has been no demonstrated

treatment benefit on long-term outcomes for the off-spring such as obesity and the development of diabetes.

It should be emphasized that although the evidence is

inconclusive that treating GDM can prevent maternal

and fetal complications, universal screening and treat-

ment are widely practiced.

Clinical Considerations andRecommendations

How should screening for GDM beaccomplished?

All pregnant patients should be screened for GDM,

whether by patients history, clinical risk factors, or a

laboratory screening test to determine blood glucose lev-

els. The optimal method of screening is controversial,

and there are insufficient data from which to draw firm

conclusions.

A number of clinical risk factors have been demon-

strated to be associated with an increased likelihood of

GDM, including age, ethnicity, obesity, family history of

diabetes, and past obstetric history (26). In one study,

more than 3,000 pregnant women underwent both the50-g, 1-hour screening test and the diagnostic oral GTT

(27). Using a complex scoring system of weighted risk

factors, the study found test thresholds for the 1-hour

screening test varied depending on individual risk status.

Sensitivity rates were similar to those of universal

screening, and one third of the subjects avoided the glu-

cose screening test. Thus, it appears it is possible to use

historic risk factors to identify individuals who may have

such a low risk for GDM that glucose challenge testing

may not be worthwhile. Conversely, there may be groups

of individuals at such high risk for GDM that it may be

more convenient and cost-effective to proceed directly to

the diagnostic GTT without obtaining the laboratoryscreening test.

Specific risk factors and the degree of their influ-

ence on GDM prevalence are difficult to quantify across

populations. For example, in one Canadian study,

African race was not associated with an increased risk of

GDM (27), whereas in another large, observational study

African race was found to be an independent predictor of

the likelihood of GDM, even when investigators con-

trolled for obesity (28). Because no single study can be

generalized to the entire population, it seems reasonable

to base the definition of high and low risk for GDM on

the prevalence of type-2 diabetes in each ethnic group.

The relationship between obesity and GDM is most like-

ly a continuum, so that the definition of the upper limit

of normal weight suggested by the Institute of Medicine(ie, a body mass index25) (29) should reasonably serve

to identify individuals who are not obese. A low-risk

individual meets all of the following criteria (30):

1. Age younger than 25 years

2. Not a member of an ethnic group with an increased

risk for the development of type-2 diabetes (exam-

ples of high-risk ethnic groups include women of

Hispanic, African, Native American, South or East

Asian, or Pacific Islands ancestry)

3. Body mass index of 25 or less

4. No previous history of abnormal glucose tolerance5. No previous history of adverse obstetric outcomes

usually associated with GDM

6. No known diabetes in first degree relative

When the 1997 criteria, similar to those listed previously

for low risk, were applied to data from more than 18,000

pregnancies in a predominantly Caucasian population,

researchers determined that only 3% of women with

GDM would not have been diagnosed (31). However,

only 10% of the population would have been exempted

from screening. For this reason, many physicians elect to

screen all pregnant patients as a practical matter.

At what gestational age should laboratory

screening be performed?

A number of studies have demonstrated that the preva-

lence of GDM increases with advancing gestation

(3236). It has been customary to recommend the 50-g,

1-hour oral glucose challenge test be administered at

2428 weeks of gestation. This arbitrary recommenda-

tion results from an attempt to balance two competing

interests. Insulin resistance increases as pregnancy pro-

gresses, therefore, testing later in pregnancy will result

in a higher yield of abnormal tests. However, the later the

abnormality is diagnosed, the less time will be availablefor intervention. Although many practitioners choose to

screen high-risk patients early in pregnancy, the benefit

of early treatment of women with GDM identified early

in pregnancy has not been demonstrated but rather has

been accepted on a theoretical basis.

Patients who had GDM in a previous pregnancy have

a 3350% likelihood of recurrence in a subsequent


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pregnancy (3739). If such patients were not tested

between pregnancies, some of these recurrences may rep-

resent preexisting diabetes undetected between pregnan-

cies. In such individuals there should still be a benefit to

making the diagnosis of diabetes during the first half of

pregnancy. Unlike typical patients with GDM, patients

with abnormal glucose tolerance in the first half of preg-

nancy may manifest severe degrees of hyperglycemia.

How is laboratory screening accomplished?

Although the use of random glucose measurements or

fasting glucose measurements have been advocated to

screen for GDM, inadequate data are available to evalu-

ate the relative effectiveness of these approaches.

Random glucose screening does not appear to be ade-

quately sensitive (40). The screening test most common-

ly used in the United States is the 50-g, 1-hour glucose

challenge, using a pure glucose load of 50 g in 150 mL of

fluid. Glucose polymer solutions, which provide a lower

osmotic load for a given glucose load, appear to be asso-ciated with fewer gastrointestinal symptoms and have

been demonstrated to yield fair correlation with

monomeric glucose solutions (4143). The use of jelly

beans instead of a pure glucose challenge has been shown

to be better tolerated, but this method has poor sensitivi-

ty (40%) when compared with glucose polymer solutions

(8090%) (44).

Among subjects with GDM, for whom the function

of the screening test is most critical, either higher (45) or

similar (46) values were reported when the test was

administered in the fasting state. Therefore, given the

lack of evidence that fasting improves the accuracy of the

screening test and the fact that fasting may pose signifi-cant logistic problems, the 50-g, 1-hour screening test

may be administered without regard to the time elapsed

since the last meal.

Should venous or capillary blood be used?

The original description of the screening test used venous

whole blood (17), but laboratories have switched from

whole blood to plasma or serum samples. Studies of the

screening test have generally used venous plasma.

Convenient and relatively inexpensive meters for meas-

uring glucose in capillary blood samples raise the possi-

bility of performing the screening test in an office settingwithout expensive and complicated laboratory equip-

ment. During fasting, capillary and venous blood have

similar glucose concentrations, but after a meal or glu-

cose challenge, capillary glucose is higher than venous

glucose. Laboratory instruments are generally checked

for quality against standard samples at regular intervals

to ensure accuracy. Precision is an important factor. Two

studies of various meters used in pregnancy demonstrat-

ed inadequate precision for all but one or two meter

systems tested (47, 48). Therefore, if capillary blood

samples are to be used for GDM screening, the precision

of the meter should be known, and its correlation with

simultaneously obtained venous samples should be

ascertained. Appropriate thresholds can then be derived.

Office-based glucose testing is not recommendedbecause of the difficulty in complying with required fed-

eral standards for testing. However, if used, it may be

most practical to continue to use venous plasma samples

and published thresholds for further testing.

Is there an appropriate threshold value for

the laboratory screening test?

The screening test threshold at which a diagnostic GTT

is recommended will be arbitrary. The higher the thresh-

old, the lower the sensitivity but the better the specific-

ity and the lower the likelihood of a false-positive test

result. The lower the threshold, the higher the sensitivitybut the higher the likelihood of a false-positive test result

and thus the performance of an unnecessary diagnostic

GTT. OSullivan and Mahan (17) used venous whole

blood samples and the Somogyi-Nelson method of glu-

cose analysis. At the recommended threshold of 130

mg/dL, the screening test had a sensitivity of 79% and a

specificity of 87%. When venous plasma and specific

enzymatic methods of glucose analysis were used, 10%

of women with GDM manifested screening test values

between 130139 mg/dL (18). Absolute sensitivity lev-

els could not be determined because women with screen-

ing test values below 130 mg/dL did not undergo oral

GTTs. When the threshold was lowered from 140 mg/dLto 130 mg/dL, the number of women requiring glucose

tolerance testing increased from 14% to 23%, or approx-

imately one quarter of patients.

Although a threshold of 140 mg/dL was recom-

mended in the past, the most recent position statement of

the American Diabetes Association ascribes a sensitivity

of approximately 80% to this cutoff and 90% sensitivity

with a threshold of 130 mg/dL and leaves the choice

open (49). Because the precise cost-benefit ratio of diag-

nosing GDM remains unresolved, either threshold is

acceptable.

How is GDM diagnosed?

The diagnostic test specific for pregnancy and about

which the greatest body of data exists is the 100-g, 3-

hour oral GTT. Diagnostic criteria were originally

derived by OSullivan and Mahan (50). Cutoff levels two

standard deviations above the mean were found to be the

best predictors for developing diabetes later in life.


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There are no well-designed studies that demonstrate

whether these diagnostic criteria are optimal to identify

pregnancies at risk for maternal or perinatal morbidity.

The relationship between maternal glucose intolerance

and adverse pregnancy outcomes appears to be more or

less continuous with no absolute threshold (4). Two sets

of criteria were adapted from the original OSullivan and

Mahan values when laboratories switched to venousplasma or serum. These samples yield results approxi-

mately 14% higher than does whole blood. The National

Diabetes Data Group published conversions derived by

adding 15% to each of the four thresholds (51). Lower

thresholds were subsequently derived by also correcting

for the change to enzymatic methods of glucose analysis

(52). Expert panels have supported both criteria, but

there are no data from clinical trials to determine which

is superior (Table 1) (53).

A positive diagnosis requires that two or more

thresholds be met or exceeded. The test is administered

in the morning after an overnight fast. Patients shouldnot smoke before the test and should remain seated dur-

ing the test. Patients should be instructed to follow an

unrestricted diet, consuming at least 150 g of carbohy-

drate per day for at least 3 days prior to the test. This

should avoid carbohydrate depletion, which could cause

spuriously high values on the GTT.

Patients with only one abnormal value have been

demonstrated to manifest increased risk for macrosomic

infants and other morbidities (54, 55). However, because

the relationship between carbohydrate metabolism,

macrosomia, and other morbidity is a continuum (4, 56),

and because not all of this morbidity arises from carbo-

hydrate intolerance, it should be anticipated that nothreshold will identify all patients at risk.

How should blood glucose be monitored in a

woman with GDM?

The optimal frequency of blood glucose testing in

patients with GDM has not been established. Whether

daily testing is essential for women with GDM has not

been proven. One large, prospective trial compared

seven-times-daily self-glucose monitoring using memo-

ry-based reflectance meters with weekly fasting and 2-

hour laboratory glucose determinations supplemented by

four-times-daily self-monitoring with only test strips and

no meters (57). The more intensively monitored group

had fewer primary cesarean deliveries and fewer macro-somic neonates, and their infants were less likely to

experience shoulder dystocia and neonatal hypo-

glycemia than the more conventionally monitored group.

Other centers have reported similar results with four-

times-daily glucose monitoring (25, 58). Although daily

self-glucose monitoring has not been demonstrated to

reduce perinatal mortality in women with GDM, it

appears to be useful in reducing potentially adverse out-

comes such as macrosomia. However, evidence from

well-designed, randomized trials that compare daily self-

glucose monitoring with less frequent assessment in

women with GDM is still needed.

Further uncertainty surrounds the timing of glucose

determinations and the selection of appropriate thresh-

olds for intervention. In nonpregnant individuals, dia-

betes is most often managed using preprandial glucose

determinations. However, the fetus may be more sensi-

tive to glucose excesses than to the nadirs of glucose val-

ues at various times of the day. In studies of preexisting

diabetes, 1-hour postprandial glucose values were found

to be more predictive of fetal macrosomia than were fast-

ing values (59), and a 1-hour value of 130 mg/dL or

more was found to be an appropriate threshold (60). A

randomized trial compared preprandial with 1-hour post-

prandial glucose measurements in 66 women whoseGDM was severe enough to require insulin treatment by

30 weeks of gestation (25). Macrosomia, neonatal hypo-

glycemia, and cesarean deliveries for shoulder dystocia

were significantly lower among those who had postpran-

dial monitoring, and their glycohemoglobin levels also

decreased more markedly than did the levels of the sub-

jects who used preprandial monitoring. No studies are

Table 1. Two Diagnostic Criteria for Gestational Diabetes Mellitus

Plasma or Serum Glucose Level Plasma Level

Status Carpenter/Coustan Conversion National Diabetes Data Group Conversion

mg/dL mmol/L mg/dL mmol/L

Fasting 95 5.3 105 5.8

One hour 180 10.0 190 10.6

Two hours 155 8.6 165 9.2

Three hours 140 7.8 145 8.0

Adapted from Expert Committee on the Diagnosis and Classification of Diabetes Mellitus. Report of the Expert Committee on the Diagnosis and Classification of DiabetesMellitus. Diab Care 2000;23(suppl 1):S4S19


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available to compare the efficacy of 1-hour postprandial

versus the more traditional 2-hour postprandial glucose

determinations.

Because these studies only included individuals

with preexisting diabetes or those with GDM severe

enough to require insulin treatment by 30 weeks of ges-

tation, it remains to be established whether fasting or

preprandial glucose measurements will suffice forindividuals with milder forms of GDM. One study

demonstrated a moderate correlation between fasting

and 2-hour postprandial glucose values in GDM; if the

fasting value was below 105 mg/dL, then only 17% of

the 2-hour values exceeded 120 mg/dL (61). Given the

available data, postprandial glucose values appear to be

most effective at determining the likelihood of macroso-

mia and other adverse pregnancy outcomes in patients

with GDM.

Is there a role for diet therapy in the treat-

ment of GDM?

Although there are no available data comparing medical

nutrition therapy (diet) with no treatment in women with

GDM, there is one such randomized trial of women who

had abnormal glucose challenge test results but normal

oral GTT results (62). Those on the prescribed diet deliv-

ered fewer macrosomic infants. Nutritional intervention

in women with GDM should be designed to achieve nor-

mal glucose levels and avoid ketosis, while maintaining

appropriate nutrition and weight gain. The American

Diabetes Association recommends nutritional counsel-

ing, if possible by a registered dietitian, with individual-

ization of the nutrition plan based on height and weight

(49). The American Diabetes Association also recom-

mends an average of 30 kcal/kg/d based on prepregnant

body weight for nonobese individuals (49). The most

appropriate diet for women with GDM has yet to be

established.

The American Diabetes Association suggests that

obese women (body mass index >30) may do well with

moderate caloric restriction (3033%) (49). Caloric

restriction of 30% in obese women with GDM was asso-

ciated with pregnancy outcomes (birth weight and

macrosomia) similar to those of a group of matched con-

trols who had normal values on the glucose challenge

screening tests (63). One concern about caloric restric-tion is that, although glucose levels may decrease, there

is the possibility that it may cause starvation ketosis (64).

Levels of glucose, free fatty acids, and ketone bodies

have been assessed during each trimester in long-term

follow-up studies of infants of women with and without

diabetes. These studies have reported an inverse associa-

tion between maternal circulating levels of ketone acids

in the second and third trimesters and psychomotor

development and intelligence in the offspring at 35

years of age and through 9 years of age (65, 66). Even

when investigators reevaluated their findings by taking

into account socioeconomic status, race or ethnicity, and

the presence of gestational or preexisting diabetes, this

association persisted. Although the correlation between

IQ and ketone levels was weak (r = 0.2), it was statisti-cally significant (P = 0.02); therefore, it would be pru-

dent to avoid excessive ketonemia or ketonuria during

pregnancy. When obese women with GDM were placed

on moderate caloric restriction (25 kcal/kg of ideal non-

pregnant weight per day), no ketonuria was detected dur-

ing weekly clinic visits (67). Serum ketones were not

reported. Available evidence does not support a recom-

mendation for or against moderate caloric restriction in

obese women with GDM. However, if caloric restriction

is used, the diet should be restricted by no more than

33%, and ketonuria should be avoided.

Supplemental dietary fiber may improve glycemiccontrol in women with type-2 diabetes. In a cohort study,

increasing dietary fiber enrichment did not improve

glucose control in patients with GDM (68). Available

evidence does not support the prescription of fiber sup-

plements for GDM.

Is there a role for insulin in the treatment of

GDM?

Some (6971) but not all (72) prospective trials have

demonstrated that insulin treatment of all women with

GDM can reduce the likelihood of delivering a macro-

somic baby. However, using such a paradigm would

require that 100% of individuals be treated although less

than half (between 9% and 40%) would benefit. It would

be preferable to select the most appropriate patients for

treatment.

One traditional approach has been to add insulin if

medical nutrition therapy does not maintain fasting plas-

ma glucose below 105 mg/dL or 2-hour values below

120 mg/dL or both. These thresholds have been extrapo-

lated from recommendations for managing pregnancy in

women with preexisting diabetes. A randomized trial

demonstrated that using a 1-hour postmeal goal of 140

mg/dL was effective in preventing adverse outcomes in

women with GDM severe enough to require insulin (25).It would be logical, although unproven, that similar

thresholds should be used for initiating insulin treatment.

A study of individuals with preexisting diabetes found

the most appropriate target 1-hour postprandial glucose

level for preventing macrosomia was 130 mg/dL (60). It

may be reasonable to apply these data to women with

GDM. Women with higher fasting glucose levels are


7/14


more likely to require insulin therapy to achieve optimal

glucose control than women with lower fasting glucose

levels. Thirty-eight percent of women with GDM with an

initial fasting plasma glucose level of 95 mg/dL or less

required insulin to achieve optimized control (mean of

seven daily values 4 kg), and neonatal hypoglycemia. Cord

serum analyses showed no detectable glyburide in the

infants. At this time, no other oral agent has been shown

to be safe and effective in GDM, and this study has not

been confirmed. Further study is recommended before

the use of newer oral hypoglycemic agents can be sup-

ported for use in pregnancy.

Is fetal assessment indicated in pregnancies

complicated by GDM?

Antepartum fetal testing is recommended for patients

with preexisting diabetes (81). If the increased risk of

fetal demise in patients with preexisting diabetes is


8/14


related to suboptimal metabolic control, it would be

expected that patients with GDM who have poor meta-

bolic control also would be at risk and thus merit

antepartum fetal surveillance. Patients with well-con-

trolled GDM are presumably at lower risk for fetal death

than are those whose condition is not well controlled or

who require insulin therapy, but there is no consensus

regarding antepartum testing in women with well-controlled GDM. There are no data available from ran-

domized trials of antepartum testing in patients with

GDM. Most case series report good outcomes with a

given testing protocol and conclude the protocol used is

appropriate. Twice-weekly nonstress tests and amniotic

fluid volume determinations were associated with no

stillbirths and a 4.9% rate of cesarean delivery for non-

reassuring fetal status in a cohort of women with GDM

who had fasting glucose levels below 105 mg/dL (82).

Another cohort study of women with GDM who

required only diet therapy and were monitored by daily

fetal movement determinations beginning at 28 weeks ofgestation and who underwent nonstress testing beginning

at 40 weeks of gestation found no stillbirths or neonatal

deaths (83). Patients requiring insulin or who had previ-

ous stillbirths, chronic hypertension, or pregnancy-

induced hypertension underwent earlier fetal testing as

did patients with preexisting diabetes. Because this latter

study lacked sufficient power to evaluate perinatal mor-

tality, it is not possible to make an unequivocal recom-

mendation. Despite the lack of conclusive data, it would

seem reasonable that women whose GDM is not well

controlled, who require insulin, or have other risk factors

such as hypertension or adverse obstetric history should

be managed the same as individuals with preexisting dia-betes. The particular antepartum test selected, whether

nonstress test, contraction stress test, or biophysical pro-

file, may be chosen according to local practice.

Ultrasonography has been used to estimate fetal

weight, especially to predict macrosomia prior to deliv-

ery. However, the reliability of these measures has not

been established (8486). Regression formulas using

combined fetal measures for weight estimates are asso-

ciated with systematic errors. Using existing formulas,

an estimated fetal weight would have to exceed 4,800 g

for the fetus to have more than a 50% chance of being

macrosomic (87, 88). In addition, the use of ultrasound-

derived measures of fetal weight have not been shown to

be superior to clinical measures.

When and how should delivery occur in

pregnancies complicated by GDM?

The timing of delivery in patients with GDM remains

relatively open. When glucose control is good and no

other complications supervene, there is no good evi-

dence to support routine delivery before 40 weeks of

gestation. In a study in which women with insulin-treat-

ed GDM and fetuses believed to be of appropriate weight

for gestational age were randomized at 38 weeks of ges-

tation to induction of labor within 1 week or expectant

management, there was no difference in cesarean deliv-

ery rates (89). However, the induction group delivered asmaller proportion of LGA babies. In a cohort multiple

time series study, a policy of induction of labor at 3839

weeks of gestation for women with insulin-treated GDM

was compared with the results in expectantly managed

historic controls (90). There was no significant differ-

ence in macrosomia or cesarean delivery rates, but

shoulder dystocia was experienced by 10% of the expec-

tant management group beyond 40 weeks of gestation

versus 1.4% in the group induced at 3839 weeks of ges-

tation. Although significant, these data have not been

confirmed by additional studies.

Available data do not address women with GDM not

treated with insulin or those believed to have macro-

somic fetuses. Individuals whose metabolic control does

not meet the goals described earlier, or is undocumented,

or those with risk factors such as hypertensive disorders

or previous stillbirth should be managed the same as

those with preexisting diabetes.

When GDM is well controlled and dates are well

documented, respiratory distress syndrome at or beyond

39 weeks of gestation is rare enough that routine amnio-

centesis for pulmonary maturity is not necessary (91). At

earlier gestational ages, or when control is poor or

undocumented, pulmonary maturity should be assessed

before induction. However, when early delivery isplanned because of maternal or fetal compromise, the

urgency of the indication should be considered in the

decision to perform amniocentesis.

Cesarean delivery rates are higher in women with

GDM compared with controls, and the difference is not

entirely attributable to fetal macrosomia (3, 9). It may be

that caregivers are more prone to perform cesarean deliv-

eries in patients with GDM because of concern about the

likelihood of shoulder dystocia. There are no data to sup-

port a policy of cesarean delivery purely on the basis of

GDM. However, macrosomia is distinctly more common

in women with GDM, and shoulder dystocia is more

likely at a given birth weight in pregnancies complicatedby diabetes than in nondiabetic pregnancies (92, 93). It

may be reasonable, therefore, to recommend cesarean

delivery without a trial of labor at some particular thresh-

old of fetal weight.

One of the problems in trying to apply such a

threshold is the poor accuracy of ultrasound prediction

of birth weight. In particular, a study reported that when


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birth weight exceeds 4,500 g, only 50% of the fetuses

weigh within 10% of the ultrasound-derived estimate

(94). A decision analytic model was developed to esti-

mate the potential effectiveness and costs of a policy of

elective cesarean delivery for fetal macrosomia diag-

nosed by ultrasonography (95). Investigators factored in

such considerations as the poor predictive accuracy of

ultrasonography, the background cesarean delivery ratesat various fetal weights, and the effect of maternal dia-

betes. The analysis predicted that in women with dia-

betes it would be necessary to perform 489 cesarean

deliveries to prevent one permanent brachial plexus

injury at a threshold of 4,000 g estimated fetal weight, or

443 cesarean deliveries at a threshold of 4,500 g esti-

mated fetal weight. These figures are one fifth to one

eighth of the figures developed for pregnancies of

women without diabetes. The authors concluded such a

policy may be tenable, although the merits are debatable.

On the basis of available data, it is not possible to deter-

mine whether the potential benefits of cesarean deliverywithout labor at a given estimated fetal weight are simi-

lar for patients with GDM and those with preexisting

diabetes. It would appear reasonable to recommend that

patients with GDM be counseled regarding possible

cesarean delivery without labor when the estimated fetal

weight is 4,500 g or greater. When the estimated weight

is 4,0004,500 g, additional factors such as the patients

past delivery history, clinical pelvimetry, and the

progress of labor may be helpful to consider in deter-

mining mode of delivery.

With an estimated fetal weight greater than 4,500 g,

prolonged second stage of labor or arrest of descent in

the second stage is an indication for cesarean delivery.Because of the higher likelihood of shoulder dystocia at

a given birth weight in the pregnancies of women with

diabetes, it may be best to apply the above recommenda-

tion to an estimated fetal weight greater than 4,000 g for

GDM. Operative deliveries from the midpelvis should be

avoided, if possible, in patients with GDM who have an

estimated fetal weight of 4,000 g or more and a pro-

longed second stage of labor (92, 96).

Should women with a history of GDM be

screened postpartum?

Women with a history of GDM are at increased risk for

developing diabetes (generally type-2 diabetes) later in

life (97, 98). Diabetes will be diagnosed in some women

soon after pregnancy, suggesting they had preexisting

diabetes that was not diagnosed prior to pregnancy.

Populations with a high prevalence of type-2 diabetes

who do not have access to screening when not pregnant

are at particularly high risk for this phenomenon (99).

Current recommendations for the diagnosis and classifi-

cation of diabetes in the nonpregnant state are based on

the recommendations of an expert committee of the

American Diabetes Association and are depicted in

Table 2 (100). Diagnostic testing for diabetes may beperformed after the immediate effects of pregnancy on

glucose metabolism have dissipated and is most conven-

ient at around the time of the postpartum checkup.

However, there are no long-term follow-up studies that

verify the benefit of postpartum diagnostic testing.

Although the American Diabetes Association advo-

cates the use of a fasting plasma glucose determination

as being less cumbersome than the oral GTT, the oral

GTT will more accurately identify those women who

had GDM and now have impaired glucose tolerance

(101). Because the presence of such a condition may be

important in counseling for future pregnancies, there

may be advantages to performing the oral GTT as theinitial diagnostic test after pregnancy complicated by

GDM. If the results of both the fasting plasma glucose

and the oral GTT are normal, subsequent follow-up tests

may use the fasting plasma glucose.

Table 2. Criteria for the Diagnosis of Diabetes Mellitus in the Nonpregnant State*

Impaired Fasting Glucose orNormal Values Impaired Glucose Tolerance Diabetes Mellitus

FPG


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The estimate of long-term risk for developing dia-

betes among women who had GDM depends on the

diagnostic test used, the duration of follow-up, age, and

other characteristics of the population studied; reported

rates vary widely (102). In follow-up studies up to 28

years on the cohort of patients used to derive the

OSullivan and Mahan criteria for GDM, diabetes was

found in 50% of women who had GDM compared with7% of controls (103). Factors identifiable during or

shortly after pregnancy that increase the risk for subse-

quent diabetes include the degree of abnormality of the

diagnostic GTT, the presence or absence of obesity, the

gestational age at diagnosis of GDM, and the degree of

abnormality of the postpartum oral GTT (104, 105).

Individuals at increased risk should be counseled regard-

ing diet, exercise, and weight reduction or maintenance

to forestall or prevent the onset of type-2 diabetes.

Summary ofRecommendations

The following recommendations are based on lim-

ited or inconsistent scientific evidence (Level B):

The laboratory screening test should consist of a

50-g, 1-hour oral glucose challenge at 2428 weeks

of gestation, which may be administered without

regard to the time of the last meal.

A screening test threshold of 140 mg/dL has 10%

less sensitivity than a threshold of 130 mg/dL but

fewer false-positive results; either threshold isacceptable.

The screening test generally should be performed on

venous plasma or serum samples using well-calibrated

and well-maintained laboratory instruments.

Available evidence does not support a recommenda-

tion for or against moderate caloric restriction in

obese women with GDM. However, if caloric

restriction is used, the diet should be restricted by no

more than 33% of calories.

For women with GDM and an estimated fetal

weight of 4,500 g or more, cesarean delivery may be

considered because it may reduce the likelihood of

permanent brachial plexus injury in the infant.

When medical nutritional therapy has not resulted in

fasting glucose levels less than 95 mg/dL or 1-hour

postprandial values less than 130140 mg/dL or 2-

hour postprandial values less than 120 mg/dL,

insulin should be considered.

The following recommendations are based prima-

rily on consensus and expert opinion (Level C):

Although universal glucose challenge screening for

GDM is the most sensitive approach, there may be

pregnant women at low risk who are less likely to

benefit from testing. Such low-risk women should

have all of the following characteristics:

1. Age younger than 25 years

2. Not a member of a racial or ethnic group with

high prevalence of diabetes (eg, Hispanic,

African, Native American, South or East

Asian, or Pacific Islands ancestry)

3. Body mass index of 25 or less

4. No history of abnormal glucose tolerance

5. No previous history of adverse pregnancy out-

comes usually associated with GDM

6. No known diabetes in first degree relative

There is insufficient evidence to determine the opti-

mal antepartum testing regimen for women with

GDM with relatively normal glucose levels on diet

therapy and no other risk factors.

Either the plasma or serum glucose level established

by Carpenter and Coustan or the plasma level desig-

nated by the National Diabetes Data Group conver-

sions are appropriate to use in the diagnosis of

GDM.

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Gestational Diabetes. ACOG Practice Bulletin No. 30. AmericanCollege of Obstetricians and Gynecologists. Obstet Gynecol2001;98:525538

The MEDLINE database, the Cochrane Library, andACOGs own internal resources and documents were usedto conduct a literature search to locate relevant articles pub-lished between January 1985 and June 2000. The searchwas restricted to articles published in the English language.Priority was given to articles reporting results of originalresearch, although review articles and commentaries also

were consulted. Abstracts of research presented at sympo-sia and scientific conferences were not considered adequatefor inclusion in this document. Guidelines published by or-ganizations or institutions such as the National Institutes ofHealth and the American College of Obstetricians and Gy-necologists were reviewed, and additional studies werelocated by reviewing bibliographies of identified articles.When reliable research was not available, expert opinionsfrom obstetriciangynecologists were used.

Studies were reviewed and evaluated for quality accordingto the method outlined by the U.S. Preventive Services TaskForce:

I Evidence obtained from at least one properly de-signed randomized controlled trial.

II-1 Evidence obtained from well-designed controlledtrials without randomization.

II-2 Evidence obtained from well-designed cohort orcasecontrol analytic studies, preferably from morethan one center or research group.

II-3 Evidence obtained from multiple time series with orwithout the intervention. Dramatic results in uncon-trolled experiments could also be regarded as thistype of evidence.

III Opinions of respected authorities, based on clinicalexperience, descriptive studies, or reports of expertcommittees.

Based on the highest level of evidence found in the data,recommendations are provided and graded according to thefollowing catetories:

Level ARecommendations are based on good and consis-tent scientific evidence.

Level BRecommendations are based on limited or incon-sistent scientific evidence.

Level CRecommendations are based primarily on con-sensus and expert opinion.

no. 30. gestational diabetes

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