Prediction of gestational age with symphysis-fundal height and estimated uterine volume in a pregnancy cohort in Sylhet, Bangladesh

Abstract

Objective: To improve the accuracy of the prediction of gestational age (GA) before birth with the standardised measurement of symphysis-fundal height (SFH), estimation of uterine volume, and statistical modelling including maternal anthropometrics and other factors.

Design: Prospective pregnancy cohort study.

Setting: Rural communities in Sylhet, Bangladesh.

Participants: 1516 women with singleton pregnancies with early pregnancy ultrasound dating (<20 weeks); 1486 completed follow-up.

Methods: SFH and abdominal girth were measured at subsequent antenatal care (ANC) visits by community health workers at 24 to 28, 32 to 36, and/or >37 weeks gestation. An estimated uterine volume (EUV) was calculated from these measures. Data on pregnancy characteristics and other maternal anthropometrics were also collected.

Primary outcome measure: GA at subsequent ANC visits, as defined by early ultrasound dating.

Results: 1486 (98%) women had at least one subsequent ANC visit, 1102 (74%) women had two subsequent ANC visits, and 748 (50%) had three visits. Using the common clinical practice of approximating the GA (in weeks) with the SFH measurement (cm), SFH systematically underestimated GA in late pregnancy (mean difference -4.4 weeks, 95% limits of agreement -12.5 to 3.7). For the classification of GA <28 weeks, SFH <26 cm had 85% sensitivity and 81% specificity; and for GA <34 weeks, SFH <29 cm had 83% sensitivity and 71% specificity. EUV had similar diagnostic accuracy. Despite rigorous statistical modelling of SFH, accounting for repeated longitudinal measurements and additional predictors, the best model without including a known last menstrual period predicted 95% of pregnancy dates within ±7.4 weeks of early ultrasound dating.

Conclusions: We were unable to predict GA with a high degree of accuracy before birth using maternal anthropometric measures and other available maternal characteristics. Efforts to improve GA dating in low- and middle-income countries before birth should focus on increasing coverage and training of ultrasonography.

Trial registration number: NCT01572532.

Keywords: estimated uterine volume; gestational age; preterm birth; symphysis fundal height; uterine fundal height.

Figure 1

(A) Relationship between estimated uterine volume, symphysis-fundal height and abdominal girth. (B) Geometrical representation of a prolate ellipsoid (source: Image created by Peter Mercator, license: https://creativecommons.org/licenses/by-sa/3.0/legalcode)

Figure 2

Diagram of relationship between gestational age, maternal anthropometrics and influencing factors.

Figure 3

(A) Symphysis-fundal height by gestational age (completed weeks) in Sylhet cohort (percentiles), with INTERGROWTH median measurements (50% percentile, dotted line), and clinical assumption (1cm=1week, dashed line). (B) Abdominal girth by gestational age in Sylhet cohort (percentiles). (C) Estimated uterine volume by gestational age in Sylhet cohort (percentiles). EUV, estimated uterine volume; GA, gestational age; SFH, symphysis-fundal height.