Sexual difference in early fetal crown-rump length versus gestational age in pregnancies arising from in vitro fertilization.

The purpose of this study was to investigate the influence of fetal sex on the crown-rump length (CRL) derived from pregnancies resulting from in vitro fertilization without the uncertain conception dating in the first trimester. With ultrasonography, we performed 334 and 353 examinations, on 88 male and 102 female fetuses, respectively. The relationship between gestational age and fetal CRL was explored with regression analysis: male CRL (mm) = 1.13 x gestational age (days) - 47.39 (r = 0.97), female CRL = 1.11 x gestational age - 46.44 (r = 0.97). These regression lines were mutually included in the 95% confidence intervals for each other. Our results indicate no statistically significant difference in the CRL between the two sexes, being supportive of using the identical fetal CRL criterion regardless of fetal sex for gestational age assessment with ultrasonography in the first trimester of pregnancy.