Sex-Specific Variation in Maternal Serum Screening Markers Across the First and Second Trimesters: Evidence from 10,384 Screened Pregnancies.

Background

Maternal serum screening remains widely implemented for prenatal aneuploidy assessment despite increased uptake of cell-free DNA testing. Evidence suggests that fetal sex may influence placental endocrine function and maternal serum biomarker levels; however, available studies are inconsistent and often limited by sample size or incomplete adjustment for maternal factors.

Objective

The aim of this study was to determine whether fetal sex independently modifies first- and second-trimester maternal serum marker Multiple of the Median (MoM) values and whether sex-related biochemical variation affects trisomy-21 screen-positive classification.

Methods

A retrospective cohort was identified from institutional screening records (10,384 screened pregnancies), of which 5040 first-trimester and 1476 second-trimester cases had complete biochemical data. First-trimester PAPP-A and free β-hCG, as well as second-trimester AFP, uE3, and free β-hCG, were measured. Implausible MoM values (<0.10 or >5.00) were excluded. Multivariable linear and logistic regression models adjusted for maternal age, maternal weight, gestational age at sampling, and parity assessed independent associations.

Results

Pregnancies with female fetuses showed significantly higher MoM values for first-trimester PAPP-A and free β-hCG as well as second-trimester AFP and uE3. The magnitude of these differences was small, and no significant differences were observed in trisomy-21 screen-positive rates between fetal sex groups.

Conclusions

Fetal sex independently influences several maternal serum markers across both trimesters but does not result in clinically meaningful differences in trisomy-21 screening outcomes under current algorithms. Any potential relevance of fetal sex for risk interpretation should be regarded as hypothesis-generating and requires outcome-validated investigation before clinical application.