SAN FRANCISCO — Ultrasound identification of placental cord insertion sites in monochorionic diamniotic twin gestations can identify pregnancies at higher risk for preterm delivery, twin-to-twin transfusion syndrome, and growth discordance, according to the findings of a retrospective study.
This information can be used to counsel patients with monochorionic diamniotic twin gestations regarding the potential fetal and neonatal morbidity and mortality risks, Dr. John Allbert reported in a poster presentation at the annual meeting of the Society for Maternal-Fetal Medicine.
A cohort of 35 twin pregnancies referred by a single perinatologist for targeted ultrasound evaluation between November 2001 and November 2005 was included in the analysis. All of the pregnancies were monochorionic diamniotic and were at less than 22 weeks' gestation at the time of ultrasound. Additionally, at the time of evaluation, both fetuses in all of the pregnancies were anatomically normal and did not meet the criteria for diagnosis of twin-to-twin transfusion syndrome (TTTS), said Dr. Allbert.
Real-time ultrasound was used to locate the placental cord insertions (PCI), and the results were confirmed with color Doppler. The insertions were then categorized as velamentous, marginal (if less than 2 cm from the placental edge), or central (2 cm or more from the edge).
On the basis of the twin pair PCIs, the pregnancies were classified into one of three groups. In group 1, the twin pair PCIs were both central. In group 2, the PCIs were either central and marginal or both marginal, and in group 3, the twin pair PCIs were central and velamentous, Dr. Allbert explained.
Of the 35 pregnancies, 11 were classified into group 1, 17 into group 2, and 7 into group 3. The groups were compared using x2 analysis or Fisher exact test for the following outcome variables: gestational age at delivery, discordant growth, TTTS, need for amnioreduction, selective laser photocoagulation therapy, preterm labor, premature rupture of membranes, perinatal mortality, preeclampsia, and chorioamnionitis.
According to the results, “both marginal and velamentous cord insertions were significantly associated with growth discordance, earlier gestational age at delivery, and a higher incidence of twin-to-twin transfusion syndrome,” said Dr. Allbert.
Specifically, the mean gestational age at delivery in group 1 was 36.4 weeks, compared with 33.6 weeks and 31.6 weeks, in groups 2 and 3, respectively. Growth discordance of at least 20% was not observed in group 1, but did occur in 29.4% and 71.4% of groups 2 and 3, respectively.
Similarly, TTTS did not occur in group 1, but did occur in 35.3% of group 2 pregnancies and in 57.1% of group 3 pregnancies.
For group 1 pregnancies, in which both cord insertion sites were at least 2 cm from the placental edge, “the pregnancy risks appeared to be similar to those of dichorionic twins,” Dr. Allbert concluded.