Role of fetal sex in amniotic fluid alphafetoprotein screening.

Abstract

Previous studies have shown that fetal gender has influence on various pregnancy complications and prenatal diagnostic biochemical markers. We have evaluated, whether elevation of amniotic fluid alphafetoprotein (AF AFP) is associated with fetal sex and whether a sex-related difference can help to identify pregnancies with AFP-associated malformations or fetal loss. From our database we obtained 6461 singleton gestations with AF AFP measurements for the period April 1997-March 1999. Patients with AF AFP >1.9 MoM were identified, details of pregnancy outcome were obtained and compared to matched-pair controls having AF AFP <2 MoM. In 232 of 262 patients having AF AFP levels >1.9 MoM outcome information was available. Of these fetuses, significantly more had male gender (147 male fetuses versus 85 female). Having a screen-positive result the risk of AFP-associated malformations was significantly higher for female fetuses (25 female fetuses (29.4%) versus 22 male fetuses (15%) with AFP-associated malformations). Adjusting the cut-off MoM to 2.5 for male and to 2.0 for female fetuses halves the false positive rate from 3.4 to 1.7% without affecting the detection rate of 95%. Pregnancies with false positive AF AFP had a significantly higher risk for fetal loss compared with pregnancies having normal AF AFP (ten fetal losses from 185 versus two fetal losses from 232), but fetal gender had no significant influence. Adjusting AF AFP MoM cut-offs for fetal gender could increase performance of AF-AFP screening. Larger studies are required to determine suitable sex-adjusted cut-off levels.