Effect of fetal gender on first trimester markers and on Down syndrome screening.

OBJECTIVES: The purpose of the present study was to evaluate whether a gender-related difference exists in first trimester markers used for Down syndrome screening, namely nuchal translucency (NT), maternal serum pregnancy-associated plasma protein-A (PAPP-A), and free beta-human chorionic gonadotrophin (beta-hCG), and whether this has an influence on screening performance. METHODS: A total of 1325 patients with a singleton pregnancy underwent combined first trimester screening at 10-13 weeks' gestation. Maternal serum PAPP-A and free beta-hCG were analyzed by fluoroimmunoassay, nuchal translucency (NT) was measured by transvaginal sonography. Only patients with normal outcomes and known fetal gender were included in the study. Data were categorized by gestational age and by fetal gender. RESULTS: There were no significant gender-related differences in NT and PAPP-A levels. However, free beta-hCG was significantly higher (p=0.00004) in the presence of a female fetus than in the presence of a male fetus. Women with female fetuses had a higher median calculated Down syndrome risk (1:5490) compared to those having males (1:6451). This difference was not, however, statistically significant. CONCLUSION: First trimester free beta-hCG is significantly higher in pregnancies with a female fetus.