The distribution of chorion and amnion types in twin pregnancies

Objective: Our aim was to determine the distribution of chorion and amnion sac types in twin pregnancies during the routine screening procedures during the first trimester, and to investigate their relevance with pregnancy being natural or by assisted reproductive technology. Methods: Twin pregnancies analyzed during routine first trimester screening were evaluated retrospectively. The twins were grouped according to their conception types which are natural birth and by assisted reproductive technologies (ART). The cases which have missing or suspicious information about chorion-amnion types and with unknown conditions for pregnancies whether they were by ART or naturally were excluded from the study. In the sonographic chorionicity distinction, the presence of classic lambda and T signs was considered. The unavailability of amniotic membrane among fetuses was defined as monoamniotic twin. Results: During 14 years, 286 twin pregnancies were considered as appropriate cases to analyze. Mean maternal age was 30.47±5.07 years, and mean week of gestation during sonography was 12.23±0.70. Double placentas were found in 83.2% of all pregnant women, and single placenta in 16.7% of all pregnant women. While 54.5% (n=156) of twin pregnancies were ART pregnancies, 45.5% of them were natural pregnancies. It was determined that 67.7% of natural twins were diamniotic dichorionic, 27.7% of them were diamniotic monochorionic and 4.6% of them were monoamniotic monochorionic while 96.2% of ART pregnancies were diamniotic dichorionic, 3.2% of them were diamniotic monochorionic and 0.6% of them were monoamniotic monochorionic. There was statistically significant difference between ART twins and natural twins in terms of chorionicity distributions (p<0.05). Conclusion: Monochorionic structure is observed more frequently in natural twins. In the follow-up of these pregnancies, early and accurate diagnosis may be the basis of early and accurate approach for the issues related with monochorionic placentation.