Fetal gender and sonographic assessment of crown-rump length: implications for multifetal pregnancy reduction.

Abstract

Fetal size is a common criterion for the selection of an individual fetus to be reduced during multifetal pregnancy reduction. We investigated whether a difference in crown-rump length (CRL) exists between male and female fetuses at 9-13 weeks' gestation. A total of 883 singleton pregnancies was evaluated at the time of chorionic villus sampling. The mean gestational age at the time of intervention was 10.9 weeks. Pregnancies were dated by certain last menstrual period (LMP). Pregnancies with uncertain dating by LMP or with a sonographic difference of gestational age > 1 week compared with LMP were excluded, as were all cases with chromosomal abnormalities. CRL differences between male and female fetuses were compared using Student's t-test. A total of 417 female and 466 male fetuses fulfilled our study criteria. Their gestational ages ranged between 9.3 and 13.9 weeks. We found no significant difference in size between the male and female fetuses. Using the CRL to guide multifetal pregnancy reduction should not result in a clinically significant selection of either gender.