Evaluation of measurement of fetal crown-rump length from ultrasonically timed ovulation and fertilization in vitro.

To assess with accuracy the development and maturity of the fetus, we evaluated fetal growth in 46 pregnant women who had conceived subsequent to ultrasonically timed ovulation. Fetal crown-rump length (CRL) was measured at gestational ages that differed by about 1 day from those previously reported. The variance in CRL measurements at each gestational age was small, and the data were normally distributed. The CRL growth curves of this and previous studies were tested using measurements from 7 pregnancies derived from in vitro fertilization (IVF). The data from IVF pregnancies were consistent with our curve, having 1 day difference to those previously reported. The gender of the fetus did not influence the CRL during the first trimester. The results suggest that fetal growth is uniform during the first trimester.