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MANAGEMENT OF POSTTERM PREGNANCY

Leslie Ablard, MDOB/GYNMowery Women’s ClinicSalina, KS

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POSTTERM = 42 WEEKS

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DEFINITION:ACOG BULLETIN 55, SEPT 2004

Postterm pregnancy refers to pregnancies that extend beyond 42 weeks gestation (294 days, or estimated date of deliver (EDD) +14 days)

Accurate pregnancy dating is critical to the diagnosis

The term “postdates” is poorly defined and should be avoided

Although some cases are a result of the inability to accurate define the EDD, many cases result from a true prolongation of gestation

Reported frequency of postterm pregnancy is 7%

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ETIOLOGIC FACTORS

Most frequent cause of prolonged gestation A. Placental Sulfatase deficiency B. Error in Dating C. Fetal Anencephaly

Other Associations Male Sex Genetic Predisposition Primiparity h/o prior postterm pregnancy

When postterm pregnancy truly exists, the most common cause is Unknown

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ASSESSMENT OF GESTATIONAL AGE

Accurate dating is important for minimizing the false diagnosis of postterm pregnancy

MOST RELIABLY AND ACCURATELY DETERMINED EARLY IN PREGNANCY

Questions at new ob visit When was the first date of your last period? Do you have regular cycles? Approx how many days between cycles? Are you sure about the given date? Where you on any birth control when you got

pregnant? When did you first find out you were pregnant?

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ACCURACY OF LMP

There are many inaccuracies in even the “surest” of LMPs Recall Delayed Ovulation Irregular cycles

Predicting delivery date by ultrasound and last menstrual period in early gestation. Obstet Gynecol. 2001 Feb;97(2):189-94.

The last menstrual period (LMP) was considered certain in 13,541

When ultrasound was used instead of certain LMP, the number of postterm pregnancies decreased from 10.3% to 2.7% (P <.001).

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ACCURACY OF LMP

Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination. Am J Obstet Gynecol. 2002 Dec;187(6):1660-6 3655 women with sure LMP LMP reports prolonged gestation 2.8 days longer on average

than ultrasound scanning, yielded substantially more postterm births (12.1% vs 3.4%), and predict delivery among term births less accurately

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ULTRASOUND DATING?

When sure LMP and US vary greater than 8% Approx 7 days up to 20 weeks 14 days between 20-30 weeks 21 days beyond 30 weeks

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RISKS TO THE FETUS

Risk of perinatal mortality (stillbirth and early neonatal deaths) TWICE that of term. 4-7 deaths vs 2-3 deaths per 1,000 deliveries Increases SIX fold and higher at 43 weeks

Uteroplacental insufficiency Meconium aspiration Intrauterine infection

Postterm pregnancy is an independent risk factor for low umbilical artery pH at delivery and low 5 min APGAR scors

Higher incidence of fetal macrosomia, although no evidence supports inducing labor as a preventative measure in such cases Prolonged labor, CPD, Shoulder Dystocia

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RISKS TO THE FETUS

Approx 20% of postterm fetuses have dysmaturity syndrome Infants with characteristics resembling chronic

IUGR from uteroplacental insufficiency Oligo, meconium aspiration, hypogycemia, seizures,

respiratory insufficency, non-reassuring fetal testing Long term sequelae not clear

One large prospective follow up study of children 1-2 yrs, general intelligence, physical milestones, and frequency of intercurrent illnesses were not significantly different between normal infants born at term and those born postterm

Fetuses born postterm are at increased risk of death within the first year- most have no known cause

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RISKS TO THE PREGNANT WOMAN

Increased labor dystocia- 9-12% vs 2-7% Increased risk in severe perineal injury

related to macrosomia- 3.3% vs 2.6% Doubled rate of c-section----endometritis,

hemorrhage, thromboembolic events ANXIETY

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ARE THERE INTERVENTIONS THAT DECREASE POSTTERM PREGNANCY?

Accurate dating by early sono---not current standard of prenatal care in the US

Membrane sweeping studies are conflicting

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WHEN SHOULD ANTENATAL TESTING BEGIN?

No studies to state when the best time to start, frequency, or type of testing to use (no one with include an unmonitored control group)

No data that testing adversely affects patients experiencing postterm pregnancy

So, DO IT

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PERINATAL MORTALITY

Figure 1. (A) The rates of stillbirth (-▪-) and infant mortality (-) for each week of gestation from 28 to 43+ weeks expressed per 1000 live births. (B) The rates of stillbirth (dark gray) and infant mortality (light gray) in the same population of 171,527 singleton births expressed as a function of 1000 ongoing (undelivered) pregnancies.

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WHAT FORM OF TESTING?

Options include: NST, BPP, modified BPP (NST with AFI), Contraction Stress Test

No single method superior Evaluation of AFI important

Definition of oligo in the postterm not been established

No vertical pocked more than 2-3 cm AFI less than 5

My choice- starting at 41 weeks- twice weekly monitoring including NST with modified BPP (NST + AFI)

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INDUCE OR WAIT

Management of “low-risk” postterm pregnancy is controversial

Factors to include- gestational age, results of antenatal testing, cervix, maternal preference

Many studies exclude those with favorable cervices

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UNFAVORABLE CERVIX

Small advantage using cervical ripening agents Several large multicenter randomized studies of

management after 40 week report favorable outcomes with routine inductions starting at 41 weeks Largest study found that routine induction at 41

weeks, found elective induction resulted in lower c-section rates primarily related to fewer c/s for non-reassuirng fetal heart rate tracings

Patient satisfaction was also higher Meta-analysis of 19 trials found that routine induction

after 41 weeks was associated with a lower rate of perinatal mortality and no increase in c/s rate and no effect on operative vag delivery, use of analgesia, or FHRA

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INDUCE AT 41 WEEKS?

Large amounts of evidence suggest that routine induction at 41 weeks gestation has fetal benefit without incurring the additional maternal risks of a higher rate of c-section.

This conclusion has not been universally accepted

Smaller studies report mixed results Two studies reported an increase in c/s rate

among certain subgroups of patients – “high risk”

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PROSTAGLANDINS FOR INDUCTION

Valuable tool Several placebo controlled trails have reported

significant changes in Bishop scores, duration of labor, lower maximum doses of oxytocin, and reduced incidence of c/s.

No standardized doses have been established Higher doses (especially PGE1) have been

associated with tachysystole and hyperstimulation resulting in non-reassuring fetal status

Lower doses are preferable with PG is used and FHR monitoring should be done routinely before and after placement

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VBAC

Do not use prostaglandins Foley bulb + pitocin

Limited evidence on the efficacy or safety of VBAC after 42 weeks- no firm recommendations can be made

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INDUCTION OF LABOR

41 weeks? Consistently shown to have no increased

morbidity/mortality even with nulliparous patients and unfavorable cervices

39 weeks? Multiparous patients appear to have no increase risk

of c/s, morbidity, mortality Do have increased use of resources Conflicting data on nulliparous Recent study found no increase risk of c/s with

unfavorable cervix after eliminating medical inductions (preeclampsia, diabetes, etc)

Elective Induction Compared With Expectant Management in Nulliparous Women With an Unfavorable Cervix

Obstetrics & Gynecology. 117(3):583-587, March 2011.

May be a baseline risk for c/s un-related to gestational age or cervix

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2447 women underwent c/s from 30 hospitals in LA and Iowa

25% c/s performed for “failure to progress” at 3 cm or less

40% of “prolonged 2nd stage” did not meet ACOG criteria (45% nulliparous)

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INDICATIONS FOR C/S

-32,443 patients undergoing c/s 2003-2009

- Obstet &Gynecol 2011

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FRIEDMAN CURVE

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ZHANG’S NEW LABOR CURVE- SEPT 2010

26,838 women in non-augmented, active labor Multiparous do not enter active labor until 5 cm Nulliparous do not ener active labor until 6 cm Labor progresses more slowly than previously described

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GIVE ‘EM A CHANCE!!

Friedman was wrong ( or wrong for today) Labor curve of modern times is slower with the

active phase in primips not occurring until 6cm dilated!

Many c-sections performed when not even in active labor

Don’t be afraid of serial inductions Use all your armamentarium- prostaglandins,

foley bulb, pitocin, AROM, FSE, IUPC, operative delivery

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SUMMARY

Postterm pregnancy may in itself be “high risk”

Establish a EDD early and as precisely as possible- early sono?

Consider antenatal testing at 41 weeks vs induction

An unfavorable cervix may not be as much of a risk factor for c-section as underlying issues- macrosomia, fetal intolerance to labor, etc.

Where is the nadir for fetal well-being and maternal outcomes? 39 weeks? 41 weeks?

Patience is important for today’s labor curve

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POSTTERM PREGNANCY IS LIKE POPCORN

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THANK YOU