Objective: To assess the diagnostic accuracy and show the prognostic influence of different ultrasonographic criteria in triplet pregnancies(TP).
Design: Retrospective study.
Setting: Tertiary care center in France.
Population: Fifty-one consecutive TP in which at least one of the children, live- or stillborn, weighed 500 g or more, and with a gestation period of at least 22 weeks.
Methods: Chorionicity, abnormal umbilical artery Doppler waveforms, intrauterine weight (IUW) <10th centile and prenatal diagnosis of fetal anomaly were studied simultaneously as prognostic criteria. Chorionicity was confirmed at birth by placental pathology.
Main outcome measures: Diagnosis of chorionicity/amnionicity and IUW <10th centile. Neonatal intensive care unit admission, occurrence of respiratory distress syndrome and perinatal mortality.
Results: Prenatal misclassification of chorionicity/amnionicity after postnatal perinatal pathology review was 12%. The positive predictive value of IUW <10th centile diagnosis was 44% for the prediction of birthweight <10th centile. Prenatal diagnosis of mono- or dichorionic placentation was associated with increased neonatal morbidity in comparison with that of trichorionic triplets. Perinatal mortality was significantly increased where mono- or dichorionic placentation was diagnosed prenatally (OR: 4.2; CI: 1.04-17), IUW <10th centile (OR: 10; CI: 2.4-41), with raised odds for abnormal umbilical Doppler measurements (OR: 9.7; CI: 2-47) and fetal anomaly (OR: 6.4; CI: 1.4-28.9).
Conclusion: Early prenatal diagnosis of chorionicity is of major importance in triplet pregnancy. Experienced sonographers must quickly evaluate any uncertain diagnosis. In cases of unknown chorionicity, other ultrasonographic criteria can highlight high-risk triplet pregnancy, but at a later stage.