To analyze the value of Down syndrome (DS) second-trimester maternal serum screening in large series of twin pregnancies.Methods
Prospective study of second-trimester maternal serum markers ‘qb;alpha fetoprotein (AFP) and free β-human chorionic gonadotrophin (β-hCG)] in 11 040 twin pregnancies, 27 of which were trisomy 21-affected. Comparison with 64 815 singleton pregnancies, of which 86 were trisomy 21-affected. Markers were expressed in multiple of median (MoM) corrected by a previously defined coefficient (2.1 for AFP and 2.07 or 2.16 for free β-hCG, dichorionic or monochorionic, respectively).Results
Trisomy 21 frequency was 1/649 for twins and 1/754 in singletons (NS). Mean detection rate was 63% (71% when both twins were affected and 60% when one was affected), versus 74.4% in singletons. False-positive rates were 10.8% in twins versus 10.3% in singletons (NS). No significant differences in MoM AFP and free β-hCG values were noted between twins and singletons (0.92 and 0.78 for AFP and 1.54 and 2.68 for free β-hCG, respectively).Conclusion
Our study demonstrates that second-trimester DS maternal serum marker screening can be performed in twin pregnancies.