Symphysis-fundus measurements in screening for small-for-dates infants: a community based study in Gloucestershire.

Symphysis-fundus charts were introduced into 50 general practitioner antenatal clinics and the hospital antenatal clinics of two obstetricians in Gloucestershire in February 1985 for a 12-month period. Of the 1139 charts analysed, the sensitivity of one or more low fundal height measurements in predicting birthweight below the tenth centile for gestational age was 51% with a specificity of 88%. In the 319 charts with four or more measurements after 26 weeks gestation a sensitivity of 65% was recorded in predicting birthweight below the tenth centile, rising to 91% in the prediction of birthweight below the fifth centile; the specificity was correspondingly 81% and 80%. The sensitivity of the test varied inversely with maternal body mass index. The mean absolute difference in pairs of observations between general practitioners, midwives and an observer was 1.5 cm. Measurement of symphysis-fundus distance is not a precise diagnostic tool but it does provide an improvement on abdominal palpation in the prediction of small-for-dates infants. The findings of this study support the use of serial symphysis-fundus measurements in community antenatal clinics. Referral for ultrasound investigation is recommended when the measurement is low.