The influence of fetal sex in screening for Down syndrome in the second trimester using AFP and free ?-hCG

Abstract

In a study of 30 802 unaffected pregnancies and 90 cases of Down syndrome I have analysed second trimester maternal serum alpha‐fetoprotein (AFP) and free β‐human chorionic gonadotrophin (β‐hCG) and grouped the data by fetal sex. In pregnancies with an unaffected female fetus maternal serum AFP was significantly lower (3%) than in the presence of a male fetus, whilst free β‐hCG was significantly raised (7%) in the presence of a female fetus. These differences led to a significantly higher false positive rate in women carrying a female fetus (5.78% versus 4.64%). In pregnancies affected by Down syndrome the median AFP in the presence of a female fetus was not significantly different to that with a male fetus (0.72 versus 0.73); similarly for free β‐hCG the difference (2.37 versus 2.48) was not statistically significant. Although the detection rate amongst male fetuses was slightly higher than in females (74% versus 66%), this was not statistically significant. Although fetal gender does appear to have a significant effect on maternal serum marker levels, leading to a higher false positive rate in females, in cases of Down syndrome there is no evidence that such marker differences are significant and consequently little evidence for any fetal gender bias in detection rates. Copyright © 2000 John Wiley & Sons, Ltd.

Fetal sex dependency of maternal vascular adaptation to pregnancy: a prospective population‐based cohort study

“…Furthermore hCG promotes angiogenesis in the uterine vasculature and blocks any immunological action by the mother on foreign invading placental cells . Previous studies show that women carrying a female fetus have higher serum levels of hCG compared with women carrying a male fetus . In our own birth cohort the same phenomenon was observed (data not shown).…”

Influence of gravidity and foetal gender on the value of screening variables in the first trimester of pregnancy

“…Only recently, however, it has been demonstrated that these gender-associated differences exist at an even earlier stage of the pregnancy. Spencer et al [3] observed, in euploid pregnancies with a female foetus, higher levels of free b-hCG and lower levels of alphafetoprotein (AFP) in the second trimester, thus contributing to higher false positive rates in female foetuses relative to male when screening for aneuploidies.…”

Maternal hormones during early pregnancy: a cross-sectional study

“…The absence of an effect of child sex on first trimester AFP has been reported also by others [30, 45]. It should be noted, however, that most studies show differences during the second trimester, with mothers of girls having lower concentrations than mothers of boys [46, 47]. No differences in maternal IGF-I by fetal sex have been reported previously [48], despite that cord blood IGF-I has been found to be higher in girls than in boys [49–51].…”