Symphysis-pubis fundal height charts to assess fetal size in women with a normal body mass index.

Objectives: To construct symphysis-pubis fundal height (SFH) charts to estimate fetal size in pregnant women with a normal body mass index (BMI) and to describe the variation of SFH measurements according to BMI.

Methods: cross sectional study was carried out at Ampara and Gampaha Districts in Sri Lanka. Women with normal nutritional and health status, normal BMI and minimal environmental constraints on fetal growth, with ultra sound confirmation of dates by fetal crown-rump length measurements between 11 weeks and 13 weeks + six days,had their SFH measured, using non-elastic tape and standard techniques, between 24 and 41 weeks gestation. Only one measurement of SFH was obtained from each pregnant woman. Linear and polynomial regression models were fitted separately to the means and standard deviations (SD) as functions of gestational age to identify the model with the best fit. Centiles were derived from the mean and SD at each gestational age.

Results: Pregnant women from the districts of Ampara (n=387) and Gampaha (n=200) were recruited. Other than a difference of -1.5 cm (95% CI -2.27 to -0.23) at 38 weeks of gestation, there were no significant differences between the SFH measurements obtained from women with normal BMI in Ampara and Gampaha Districts. Using the SFH measurements from the Ampara sample, charts were created for 10th, 50th and 90th centile values of SFH. At 40 weeks of gestation these were 34 cm, 37 cm and 41 cm respectively. At 40 weeks gestation, the variation in SFH measurements between BMI sub groups within the normal range was approximately 1.4 cm to 1.6 cm.

Conclusions: These SFH charts could be used to estimate fetal size in pregnant women with normal BMI.