Symphysis-fundus height: construction of a new Swedish reference curve, based on ultrasonically dated pregnancies.

Repeated measurements of the symphysis-fundus (SF) distance is generally regarded as an acceptable screening instrument for antenatal detection of intrauterine growth retardation (IUGR). In the present investigation an SF curve is constructed, based on measurements from 1650 Swedish women with ultrasound dated pregnancies. The SF measurements were included in a cross-sectional stratified manner; only one measurement from each woman was used and the same number of measurements (n = 75) was used for each gestational week from 20 through 41. A regression analysis by a polynomial equation of third degree was applied on the means and standard deviations of the SF measurements in each week respectively to construct a graph of fundal height. This SF curve was compared with the SF curve in common use in Sweden (constructed by Westin); in the new curve the mean measurement was about one cm higher up to 37 gestational weeks, after which time the curves almost coincided. Neither did the mean SF height differ between smokers and non-smokers nor between nulliparous and parous women. The mean SF difference between the heaviest women (> or = 79 kg) and the lightest (> or = 53 kg) was about two cm throughout pregnancy. The validity of the constructed SF curve as a screening instrument for IUGR needs to be investigated in a different study.