Unconditional and conditional standards for fetal abdominal circumference and estimated fetal weight in an ethnic Chinese population: a birth cohort study

Abstract

Background: Diagnosis of intrauterine fetal growth restriction and prediction of small-for-gestation age are often based on fetal abdominal circumference or estimated fetal weight (EFW). The present study aims to create unconditional (cross-sectional) and conditional (longitudinal) standards of fetal abdominal circumference and EFW for use in an ethnic Chinese population.

Methods: In the Growing Up in Singapore Towards healthy Outcome (GUSTO) birth cohort study in Singapore, fetal biometric measurements were obtained at enrolment to antenatal care (11-12 weeks) and up to three more time points during pregnancy. Singleton pregnancies with a healthy profile defined by maternal, pregnancy and fetal characteristics and birth outcomes were selected for this analysis. The Hadlock algorithm was used to calculate EFW. Mixed effects model was used to establish unconditional and conditional standards in z-scores and percentiles for both genders pooled and for each gender separately.

Results: A total of 313 women were included, of whom 294 had 3 and 19 had 2 ultrasound scans other than the gestational age dating scan. Fetal abdominal circumference showed a roughly linear trajectory from 18 to 36 weeks of gestation, while EFW showed an accelerating trajectory. Gender differences were more pronounced in the 10(th) percentile than the 50(th) or 90(th) percentiles. As compared to other published charts, this population showed growth trajectories that started low but caught up at later gestations.

Conclusions: Unconditional and conditional standards for monitoring fetal size and fetal growth in terms of abdominal circumference and EFW are available for this ethnic-Chinese population. Electronic spreadsheets are provided for their implementation.

Fig. 1

Unconditional chart for abdominal circumference pooling both genders (solid lines: 5th, 50th and 95th percentiles; long dashed lines: 10th and 90th percentiles; short dashed lines: 25th and 75th percentiles). Tick marks at multiples of 5 mm from 100 to 350 mm on the vertical axis, and at single day on the horizontal axis

Fig. 2

Unconditional gender-specific 10th, 50th and 90th percentiles for abdominal circumference (solid lines for males and broken lines for females)

Fig. 3

Unconditional chart for estimated fetal weight (EFW) pooling both genders (solid lines: 5th, 50th and 95th percentiles; long dashed lines: 10th and 90th percentiles; short dashed lines: 25th and 75th percentiles). Tick marks at multiples of 50 grams from 100 to 3200 grams on the vertical axis, and at single day on the horizontal axis

Fig. 4

Unconditional gender-specific 10th, 50th and 90th percentiles for estimated fetal weight (EFW) (solid lines for males and broken lines for females)

Fig. 5

Conditional versus unconditional EFW standards for participant ID “020-66086”: a foetus (●) whose EFW was 1138 grams at gestational age of 27.7 weeks (i.e. 27 weeks + 5 days) and 2024 grams at gestational age of 33.7 weeks (i.e. 33 weeks + 5 days). (Broken lines from bottom to top: unconditional 10th, 50th and 90th percentiles. Solid lines from bottom to top: conditional 10th, 50th and 90th percentiles)