Predictive value of ultrasound measurement in early pregnancy: a randomized controlled trial

Early fetal biparietal diameter (BPD) measurements were obtained with ultrasound in 1062 women attending for antenatal care; a random half had the results withheld from the obstetricians. Of the 1026 women who were sure of the dates of their last normal menstrual period, 829 (81%) were found to have appropriate biparietal diameter measurements, in 3% the pregnancy was more than 2 weeks further advanced and in 14% more than 2 weeks less than calculated. In 30% of the women whose results were intended to be withheld, the code had to be broken because of clinical concern. There were no differences in fetal outcome (birthweight centile, Apgar score at 1 min and perinatal mortality) in the women whose BPD results were known compared with those whose results were withheld from the obstetrician. But a significantly larger number of labours were induced for suspected growth retardation when the gestational age was known.