Prenatal diagnosis of Down syndrome in dizygotic twin pregnancy.

We present a case of a 33-year-old pregnant woman who had a transvaginal ultrasound performed at week 9 of gestation. A dichorionic diamniotic twin pregnancy with symmetrically developing fetuses, was confirmed. Chromosomal defect markers (NT NB, DV TV) were analyzed in the first genetic test, performed according to the Fetal Medicine Foundation (FMF) criteria, and the double marker test was performed (PAPP-A protein and free beta-hCG concentrations in patient serum were determined). In the subsequent diagnostic procedures, the patient was offered and consented to amniopuncture after week 15 of gestation. The material obtained in the course of that invasive procedure allowed to identify a normal male karyotype - 46, XY in the first fetus (Fetus I). Cytogenetic analysis of the material from the second fetus (Fetus II) resulted in the diagnosis of an abnormal female karyotype - 47, XX, +21. Based on the analyzed clinical case, we present the difficulties of performing prenatal diagnosis in a dizygotic twin pregnancy The results prove the applicability and efficacy of prenatal diagnostics tests based on the FMF criteria also in twin pregnancies.