Decreased maternal serum hCG levels with increasing gravidity and parity

To investigate the preliminary observation that primigravid women have higher hCG multiples of the median (MoM) than multigravid women.

An analysis of the effect of gravidity and parity on maternal serum alpha-fetoprotein (MSAFP) and hCG was performed using data from 20,009 consecutive singleton pregnancies of 15-20 weeks' gestation in a maternal serum screening program.

The human chorionic gonadotropin MoM for primigravid women was 0.1 MoM higher than for multigravid women. As parity or gravidity increased, maternal serum hCG decreased. The median hCG MoM for nulliparous women was 1.05, compared with 0.94 MoM for para 3 women. The decrease in hCG was similar at each gestational week from 15-20. In contrast, MSAFP and MSAFP MoM were unaffected by parity. Maternal age and race were potential contributing factors to the effect of parity. However, the decrease in hCG MoM with parity was observed within each 5-year increment of maternal age. Similarly, both black and non-black populations displayed decreases in hCG with parity, although black women had a consistently higher MoM in all matched sets. The decrease in hCG MoM with parity was also observed in 50 Down syndrome cases. Correcting patient data for parity resulted in the hCG MoM changing only 2.7% on average. The detection rate for the 50 Down syndrome cases would not have changed.

The decrease in maternal serum hCG with increasing parity demonstrates that pregnancy history influences the level of maternal serum hCG. Further studies are needed to define the contributing factors, but the impact of parity on Down syndrome screening appears to be small.