Distributions of current and new first-trimester Down syndrome screening markers in twin pregnancies

To study the distributions of pregnancy-associated plasma protein A (PAPP-A), the free beta subunit of human chorion gonadotrophin (fbeta-hCG), A Disintegrin and Metalloprotease 12 (ADAM12) and Placental Protein 13 (PP13) in first trimester twin pregnancies.

Serum marker concentrations were measured in monochorionic and dichorionic twin pregnancies and singleton controls to study differences in multiples of the gestation-specific normal medians (MoMs).

Median PAPP-A and fbeta-hCG MoMs were 2.03 and 1.87 for monochorionic twins (n = 116) and 2.18 and 1.89 for dichorionic twins (n = 650). Furthermore, ADAM12 and PP13 MoMs were 1.66 and 1.56 for monochorionic twins (n = 51) and 1.64 and 1.53 for dichorionic twins (n = 249). No statistically significant differences between monochorionic and dichorionic twin pregnancies were found. Correlations between markers in these pregnancies did not differ from singletons.

For first-trimester screening, different parameters for monochorionic and dichorionic twin pregnancies is not necessary. Furthermore, if ADAM12 and PP13 will be adopted as screening markers, the presented median MoM values, standard deviations and correlation coefficients for twin pregnancies may contribute to a proper twin risk estimation.