prenatal assessment of gestational age - case presentation

Prenatal Assessment of Gestational Age - Case PresentationNawras Al Halabi - NawrasAlHalabi.com

Salam Sulayman - [email protected]

Medical History

• A woman is referred from the general practitioner for pregnancy dating. She had a positive pregnancy test 3 days ago after she realized that she had missed a period.

• In the past she had a regular cycles bleeding for 5 days every 28 days. However she had been taking the combined oral contraceptive pill (COCP) for the last 6 years and stopped only 10 weeks ago.

• She had a withdrawal bleed at the end of the last packet, followed by an apparently normal period 5 weeks later. She has had no other irregular bleeding or any abdominal pain. She has had regular intercourse throughout the time since she stopped her COCP and is pleased now to be pregnant.

Investigations

• Transvaginal Ultrasound findings are shown:

Questions

• How can pregnancies be dated and what is the approximate gestational age for this pregnancy?

• What further investigations would you like to do to confirm this?

• Why is correct early pregnancy dating important?

Assessment of gestational age

Importance of reliable pregnancy dating

Important for the mother, who wants to know when to expect the birth of her

baby.

This information

related to gestational is

invaluable!


• Important for Health care providers:Most obstetrical management decisions are

strongly influenced by consideration of

fetal age

which closely correlates

with

fetal development


Appropriate timing of gestation age-related testing

Avoid iatrogenic newborn prematurity

Decisions regarding delivery timing

Decisions regarding treatment of PTL or PPROM

Determine when to initiate post term fetal surveillance.

Length of pregnancies

Hamster 16-23

Lion 108

Human 280

(40 weeks)

Horse 330–342

Whale (sperm) 480–590

Elephant (African)

645

Sonographic Assessment

Clinical Assessment

Naegele's rule

Uterine Size

Methods

Methods – Clinical Assessment

Methods – Naegele's rule• Most common method of pregnancy dating.

• Using the date of the last menstrual period (LMP) To calculate the Estimated Date of Delivery ("due date" or EDD).

EDD = LMP – 3 months + 7 days.

Methods – Naegele's rule

Examples:

LMP = February 20 EDD = November 27

Methods – Naegele's rule

Example:

LMP = May 28 EDD = March 4

Methods – Naegele's ruleInaccuracy occurs because:

Many women do not have regular 28-day cycles or conceive on day 14.

Many others are not certain of the date of their last period.

Early pregnancy bleeding or the presence of light bleeding.

Oral Contraceptive Pills (OCP).

Breastfeeding.

incorrect assumption of the date of ovulation

Calculators for EDD

Physical examination

Often described in terms of fruit!

The uterus remains a pelvic organ until approximately 12 weeks of gestation

It becomes Sufficiently large to palpate abdominally just above the symphysis pubis.

Methods - Uterine size

Methods - Uterine size

At 16 weeks, the uterine fundus is palpable Midway between the Symphysis Pubis and Umbilicus

at 20 weeks it is palpable at the level of the Umbilicus

At 36 weeks it is palpable at the level of the Xiphoid process

At 40 weeks it is decline away from the Xiphoid process

36 weeks

32 weeks

26 weeks

20 weeks

16 weeks

12 weeks

36 weeks

40 weeks

Leiomyoma Obesity

Uterine malposition Multiple gestation.

What interferes with accurate assessment

Other factors

affecting uterine size

or the ability to

palpate the uterus.

Methods - Sonographic assessment

Methods - Sonographic assessment• Ultrasound estimation of EDD in the first half of pregnancy is superior to

dating based on the last menstrual period or physical examination.

1. Mongelli M, Wilcox M, Gardosi J. Estimating the date of confinement: ultrasonographic biometry versus certain menstrual dates. Am J Obstet Gynecol 1996; 174:278.

2. Neilson JP. Ultrasound for fetal assessment in early pregnancy. Cochrane Database Syst Rev 2000; :CD000182.3. Yang H, Kramer MS, Platt RW, et al. How does early ultrasound scan estimation of gestational age lead to higher rates of preterm birth? Am J Obstet Gynecol 2002; 186:433.

One study of 34,249 singleton pregnancies reported that delivery occurred within seven days of the EDD more often when sonography alone1.

A systematic review found reduced rates of induction of labor for postterm pregnancy2.

A study of 44,623 women found that sonographic dating resulted in a small downward estimation of gestational age more often than an upward estimation

Methods - Sonographic assessment1

• 1 dayIVF

• 3 daysOvulation

• 3 daysIUI

• 2 weeks1st trimester

• 4 weeks2nd trimester

• 6 weeks3rd trimester

Parameter Variability 2SD Parameter Variability 2SD

1. Callen PW. Ultrasonography In obstetrics and gynecology. 5th ed. Sauders Elsevier; 2008;p. 3-25.

Methods - Sonographic assessment• Menstrual cycles are irregular.

• Last menstrual period is unknown.

• Patients who conceive while using hormonal contraception.

• Uterine size estimated on physical examination differs from that predicted by menstrual dating.

During 1st trimester: Typically obtained by transvaginal ultrasound examination

Methods - Sonographic assessment1st trimester

Gestational sac

It is usually visible at 4.5 to 5 weeks of gestation.

It is the first sonographic sign of an intrauterine pregnancy

Double decidual sign appearing at 5.5 to 6 weeks


Gestational sac • The cursors should be placed on the sac itself and should not include the

echogenic region surrounding the gestational sac.


Gestational sac • A size of 2 to 3 mm is the smallest size that can be clearly visualized

within the uterine cavity = approximately 4 weeks and 1 to 3 days.

• Mean Sac Diameter (MSD): derived by calculating the mean of the three orthogonal sac diameter measurements.

30 sac size (mm)

Gestational age (days)

GS Week 4

Week 5 Week 6


Yolk sac• The first anatomic structure to appear within the

gestational sac.

• Provides confirmation of an intrauterine pregnancy.

• Noted initially at the beginning of the 5th week of gestation(MSD approximately 5 mm); Appear when MSD approaches 8 mm.

• Abnormal gestation are MSD of 8 mm or greater with an absent yolk sac.


Yolk sac• The yolk sac continues to grow to a maximum diameter of

approximately 6 mm by 10 weeks of gestation.

• The yolk sac migrates to the periphery of the chorionic cavity, and becomes undetectable sonographically by the end of the first trimester.

The embryonic disc becomes visible at

1 to 2 mm in length

gestational age of5 to 6 weeks.

Crown rump length (CRL)• Is the standard biometric measurement of the

embryo in the first trimester(age up to 14 weeks).

• Is the longest straight-line measurement of the embryo measured from the outer margin of the cephalic pole to the rump.



Crown rump length (CRL):• Standard practice for determining gestational

age is to take the mean of three CRL measurements.

• Accuracy:• 7-10 weeks; ±3 days.• 10-14 weeks; ±5 days.• 15 weeks; ± 8.4 days.

1. Ohuma EO, Papageorghiou AT, Villar J, Altman DG (2013). "Estimation of gestational age in early pregnancy from crown-rump length when gestational age range is truncated: the case study of the INTERGROWTH-21st Project". BMC Med Res Methodol 13: 151. doi:10.1186/1471-2288-13-151. PMC 4029763. PMID 24314232

1

12w16.7mm; 8w 1d

CRL < 25 mm 42 CRL (mm)

GA (days)

1. Goldstein SR, Wolfson R. Endovaginal ultrasonographic measurement of early embryonic size as a means of assessing gestational age. J Ultrasound Med 1994; 13:27.

2. Ohuma EO, Papageorghiou AT, Villar J, Altman DG (2013). "Estimation of gestational age in early pregnancy from crown-rump length when gestational age range is truncated: the case study of the INTERGROWTH-21st Project". BMC Med Res Methodol 13: 151. doi:10.1186/1471-2288-13-151. PMC 4029763. PMID 24314232

1

2

A: Gestational sac (GS)B: Crown rump length (CRL) of embryo

C: Amniotic sac; D: Yolk sac


Cardiac activity• Detection of cardiac activity establishes a

gestational age of 5.5 to 6 weeks.

6w, 7w

Methods - Sonographic assessment2st and 3rd trimester

During 2st and 3rd trimester: Typically obtained by transabdominal ultrasound examination

Biparietal diameter

(BPD)

Head circumference

(HC)

Abdominal circumference

(AC)

Femur length(FL)

Standard biometric parameters 2st and 3rd trimester


Biparietal diameter (BPD)• The best studied biometric parameter

• Accuracy:• 14-20 weeks; ±7 days• Mid-late 3rd trimester, = ±(3-4) weeks.

• BPD is measured on a plane of section that intersects both the third ventricle and thalami.

Methods - Sonographic assessment2st and 3rd trimester• The fetal cranium may not always display

a traditional shape.

• Cephalic index (CI):the ratio ofBPD / occipitofrontal diameter (OFD) × 100.

• The standard CI range for normal shaped craniums approximates one standard deviation from the mean (>74 or <83).

• ⇨ CI measurement approaches the outer limits of the normal range, the use of the BPD for estimation of gestational age is not accurate.


• Accuracy:• Prior to 20 weeks; ±1 week.• Late third trimester; ±(3-4) weeks.

• The correct plane for the image passes through the thalami and third ventricle.

Head circumference (HC)• Provides a good estimate of

gestational age on routine sonograms.

• Also is useful in the clinical setting of growth disorders.


Abdominal Circumference (AC)• Appears to have a slightly lower ability to predict gestational age early

in the second trimester than the BPD, HC, and FL.

• Some of the variability may be due to error in ultrasound technique, along with natural biologic variations.

• Accuracy:• Second trimester; ±2 weeks.• Late third trimester; ±(3-4) weeks.


Abdominal Circumference (AC)• AC is often used for estimations of fetal weight and interval growth

evaluations rather than gestational age assessment.

• The image is taken at the level of the largest diameter of the fetal liver, denoted by the point of union of the right and left portal veins, which has a "hockey stick" appearance.

• The correct plane can be confirmed by visualizing the umbilical segment of the left portal vein in its shortest length


Femur length (FL)• Can be measured as early as 10 weeks gestational age because of its size

and echogenicity.

• Accuracy:• Prior to 20 weeks; ±1 week;

3rd trimester; ±(2.1-3.5) weeks.

• Average femur length appears to vary slightly among ethnic groups.

Methods - Sonographic assessment2st and 3rd trimesterFemur length (FL)• Short femurs may be a normal finding or a marker of aneuploidy

(trisomy 21).

• Severely shortened (<5th percentile) or abnormal appearing femurs in the second trimester suggest a skeletal dysplasia or early onset fetal growth restriction

Other biometric parameters

Interorbital diameters

Transverse cerebellar diameter

Clavicle length

Foot length

Length of long bones of the extremities


Interorbital diameters


Transverse cerebellar diameter


Clavicle length


Foot length


Length of long bones of the extremities

Use of multiple markers

• Various fetal body ratio indexes:

• Define how these measurements correlate in an average fetus.

• Determine if a parameter is potentially abnormal.

HC/ACBPD/

FLFL/AC

Use of multiple markers

• After a careful assessment, it is usually appropriate to omit a single discordant parameter from the gestational age calculation.

• Additional measurements may be useful when there are biometric discrepancies.

• Ex: The transverse cerebellar diameter (in millimeters) correlates with gestational age up to 22 weeks of gestation.

Signs of fetal maturity

When an early ultrasound examination has not been performed or menstrual dates are unknown or uncertain.

There are several signs suggestive of fetal maturity that can be observed sonographically and correlated with gestational age.

Signs of fetal maturity

• Ex: the femoral epiphyseal and proximal tibial ossification centers are well visualized by 32 and 35 weeks gestational age, respectively

• The proximal humeral epiphysis also appears in the late third trimester and correlates with fetal lung maturity and gestational age

Combined oral contraceptive pill (COCP)

• Often referred to as the birth control pill.

• Combination of an estrogen (estradiol) and progesterone (progestin).

• When taken by mouth every day, these pills inhibit female fertility.

• The most side effect is withdrawal bleeding.

Answering questions!

Medical History

• A woman is referred from the general practitioner for pregnancy dating. She had a positive pregnancy test 3 days ago after she realized that she had missed a period.

• In the past she had a regular cycles bleeding for 5 days every 28 days. However she had been taking the combined oral contraceptive pill (COCP) for the last 6 years and stopped only 10 weeks ago.

• She had a withdrawal bleed at the end of the last packet, followed by an apparently normal period 5 weeks later. She has had no other irregular bleeding or any abdominal pain. She has had regular intercourse throughout the time since she stopped her COCP and is pleased now to be pregnant.

Investigations

• Transvaginal Ultrasound findings are shown:

Questions

How can pregnancies be dated and what is the approximate gestational age for this pregnancy?


Clinical Assessment

Naegele's rule

Uterine Size

Methods

Clinical Assessment

Naegele's rule

The uterus remains a pelvic organ until approximately 12 weeks of gestation

It becomes Sufficiently large to

palpate abdominally just above the

symphysis pubis.

Clinical Assessment

Uterine Size

12 weeks

Questions

What further investigations would you like to do to confirm this?


First sonographic sign of an

intrauterine pregnancy

Visible at 4.5 to 5 weeks

Gestational Sac


Yolk Sac

The first anatomic structure to

appear within the gestational sac.

Provides confirmation of an

intrauterine pregnancy.

Noted initially at the beginning of the 5th week of

gestation

The embryonic disc becomes visible at

1 to 2 mm in length

gestational age of5 to 6 weeks.


Cardiac activity

Detection of cardiac activity establishes a

gestational age of5.5 to 6 weeks.

First trimester screeningFIRST TRIMESTER COMBINED TESTMaternal serum beta human chorionic gonadotropin (beta-hCG)

Maternal serum pregnancy-associated plasma protein-A (PAPP-A)

Ultrasound measurement of nuchal translucency (NT)

To detect Down Syndrome and Trisomy 18

Questions

Why is correct early pregnancy dating important?


Important for the mother, who wants to know when to expect the birth of her

baby.

This information

related to gestational is

invaluable!


• Important for Health care providers:Most obstetrical management decisions are

strongly influenced by consideration of

fetal age

which closely correlates

with

fetal development


Appropriate timing of gestation age-related testing

Avoid iatrogenic newborn prematurity

Decisions regarding delivery timing

Decisions regarding treatment of PTL or PPROM

Determine when to initiate post term fetal surveillance.

Thank you!

prenatal assessment of gestational age - case presentation

Healthcare