1- Serviço de Ginecologia Obstetrícia, Centro de Diagnóstico Pré-Natal, Hospital de Dona Estefânia, Centro Hospitalar de Lisboa Central, E.P.E.;
2 - Unidade de Citogenética INSA Dr. Ricardo Jorge.
- COGI, Congresso Internacional 2012 (poster).
Problem Statement: Assisted reproduction methods are associated with a higher incidence of twin pregnancies and increased chromosome aberrations risk. Amniocentesis and chorionic villus (CVS) sampling may be used for prenatal diagnosis, the latter having the disadvantage of occasional placental mosaicism (1-2% of cases). Mosaicism may only affect the placenta [confined placental mosaicism (CPM)] or extend to the fetus [true fetal mosaicism (TFM)]. In this case, an amniocentesis should be performed to confirm the results.
Methods: We describe a case-report on a dichorionic twin pregnancy with CVS compatible with trisomy 2 and 18, found to correspond to CPM after amniocentesis.
Results: 31-year-old, OI 1-0-0-1, with a dichorionic (DC) twin pregnancy following in vitro fertilization. At 10+6 weeks, ultrasound showed umbilical hernia/omphalocele and low crown-rump length in twin B; a CVS was then performed, transcervically and transabdominally on twin A and B placenta, respectively. Trisomy 2 and 18 were found, respectively, in twin A and B. Amniocentesis was performed at 17+5 weeks of gestation and showed normal 46,XX karyotype for both twins. The karyotype discrepancies were a consequence of CPM. Follow-up ultrasound revealed no developmental abnormalities. Delivery occurred at 35 weeks by C-section without intercurrences. The placentas were normal on gross examination and dichorionicity was confirmed. Karyotype analysis of both twins' peripheral blood samples revealed a normal 46,XX.
Conclusion: To our knowledge this is the first reported case of twin pregnancy where CPM for two different chromosome pair coexist and in which one of them is one of the common primary trisomies.
Keywords: chorionic villus, amniocentesis, twin pregnancy, placental mosaicism.