Prenatal diagnosis and obstetric outcomes in triplet pregnancies in relation to chorionicity

OBJECTIVE: This study describes the frequency, pregnancy complications and outcomes of non-trichorionic triplet pregnancies. DESIGN: A retrospective observational study. SETTING: Two tertiary level referral centres of Obstetrics and Prenatal Medicine, Germany. POPULATION: All women booked to receive targeted ultrasound screening between January 1998 and June 2003. The mixed low and high risk population included 36,430 women with ultrasound examinations between 11 and 24 weeks of gestation. Of those with available outcome, 176 were triplet pregnancies with three viable fetuses. METHODS: Analysis of ultrasound data and perinatal outcome in triplet gestations who had first and second trimester targeted ultrasound examination. Pregnancies with monochorionic or dichorionic placentation were identified and pregnancy outcome was compared to trichorionic triplets. MAIN OUTCOME MEASURES: Intrauterine fetal death, fetal growth restriction (FGR), mean discordance and survival rate in non-trichorionic versus trichorionic triplets. RESULTS: Triplets were trichorionic in 81.8% and had a monochorionic or dichorionic placentation in the remaining 18.2%. The rate of monochorionicity and dichorionicity was significantly higher after spontaneous conception than after assisted reproductive technologies (44.8%vs 12.9%, P < 0.001). In non-reduced monochorionic and dichorionic triplets compared with non-reduced trichorionic triplets, there was a higher rate of intrauterine fetal death (8.8%vs 1.5%, P < 0.01), FGR (33.3%vs 25.5%), mean discordance (20.5%vs 12.7%, P < 0.01), discordance >30% (26.3%vs 2.9%, P < 0.01) and delivery <32 weeks of gestations (47.4%vs 32.2%). There was a lower survival rate in non-trichorionic triplets (84.2%) than in trichorionic ones (91.7%). CONCLUSION: Triplet pregnancies with a monochorionic or dichorionic placentation are at significantly higher risk of adverse pregnancy outcome compared with trichorionic pregnancies. First trimester evaluation of chorionicity is strongly emphasised.