International standards for symphysis-fundal height based on serial measurements from the Fetal Growth Longitudinal Study of the INTERGROWTH-21st Project: prospective cohort study in eight countries

Abstract

Objective: To create international symphysis-fundal height standards derived from pregnancies of healthy women with good maternal and perinatal outcomes.

Design: Prospective longitudinal observational study.

Setting: Eight geographically diverse urban regions in Brazil, China, India, Italy, Kenya, Oman, United Kingdom, and United States.

Participants: Healthy, well nourished pregnant women enrolled into the Fetal Growth Longitudinal Study component of the INTERGROWTH-21st Project at 9-14 weeks' gestation, and followed up until birth.

Main outcome measures: Symphysis-fundal height was measured every five weeks from 14 weeks' gestation until birth using standardised methods and dedicated research staff who were blinded to the symphysis-fundal height measurements by turning the tape measure so that numbers were not visible during examination. The best fitting curve was selected using second degree fractional polynomials and further modelled in a multilevel framework to account for the longitudinal design of the study.

Results: Of 13 108 women screened in the first trimester, 4607 (35.1%) met the study entry criteria. Of the eligible women, 4321 (93.8%) had pregnancies without major complications and delivered live singletons without congenital malformations. The median number of symphysis-fundal height measurements was 5.0 (range 1-7); 3976 (92.0%) women had four or more measurements. Symphysis-fundal height measurements increased almost linearly with gestational age; data were used to determine fitted 3rd, 50th, and 97th centile curves, which showed excellent agreement with observed values.

Conclusions: This study presents international standards to measure symphysis-fundal height as a first level screening tool for fetal growth disturbances.

Conflict of interest statement

All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf and declare: support from the Bill & Melinda Gates Foundation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

Figures

Fig 1 Flowchart of recruitment of participants through the study. SFH=symphysis-fundal height

Fig 2 Scatterplot showing symphysis-fundal height (SFH) with gestational age. Lines=fitted smoothed 3rd (bottom dashed line), 50th (middle solid line), and 97th (top dashed line) centile curves; open blue circles=empirical values for each week of gestation; grey circles=actual observations

Fig 3 International symphysis-fundal height (SFH) standards for clinical use. Lines (from bottom to top)=3rd, 10th, 50th, 90th, and 97th centiles. A printable chart is available in the supplementary appendix (can also be found at https://intergrowth21.tghn.org/ under “INTERGROWTH Standards & Tools”)

Fig 4 Gestational age as a function of symphysis-fundal height (SFH). Lines=10th (bottom dashed line), 50th (middle solid line), and 90th (top dashed line) centiles; grey circles=actual observations; blue circles=simulated data to overcome truncation (see text for details)

Fig 5 Bland Altman plot of intraobserver variation of symphysis-fundal height (SFH) measurement; the central line shows the mean difference between observation 1 and 2 (solid line, 0.07 cm) while the dashed lines show the 95% limits of agreement (upper dashed line 0.66cm, lower dashed line 0.81 cm)