Between 2005 and 2021, mode of delivery of diamniotic twins at this practice did not significantly differ by chorionicity, researchers affiliated with Maternal Fetal Medicine Associates and the department of obstetrics, gynecology, and reproductive science at Icahn School of Medicine at Mount Sinai, New York reported in Obstetrics & Gynecology.
The study supports a recommendation from the American College of Obstetricians and Gynecologists that vaginal delivery “is a reasonable option in well selected diamniotic twin pregnancies, irrespective of chorionicity, and should be considered, provided that an experienced obstetrician is available,” said Iris Krishna, MD, assistant professor of maternal-fetal medicine at Emory University, Atlanta.
Dr. Iris Krishna
The experience at this practice, however, may not apply to many practices in the United States, said Dr. Krishna, who was not involved in the study.
Of 1,121 diamniotic twin pregnancies included in the analysis, 202 (18%) were monochorionic. The cesarean delivery rate was not significantly different between groups: 61% for monochorionic and 63% for dichorionic pregnancies.
Among women with planned vaginal delivery (101 monochorionic pregnancies and 422 dichorionic pregnancies), the cesarean delivery rate likewise did not significantly differ by chorionicity. Twenty-two percent of the monochorionic pregnancies and 21% of the dichorionic pregnancies in this subgroup had a cesarean delivery.
Among patients with a vaginal delivery of twin A, chorionicity was not associated with mode of delivery for twin B. Combined vaginal-cesarean deliveries occurred less than 1% of the time, and breech extraction of twin B occurred approximately 75% of the time, regardless of chorionicity.
The researchers also compared neonatal outcomes for monochorionic-diamniotic twin pregnancies at or after 34 weeks of gestation, based on the intended mode of delivery (95 women with planned vaginal delivery and 68 with planned cesarean delivery). Neonatal outcomes generally were similar, although the incidence of mechanical ventilation was less common in cases with planned vaginal delivery (7% vs. 21%).
“Our data affirm that an attempt at a vaginal birth for twin pregnancies, without contraindications to vaginal delivery and regardless of chorionicity, is reasonable and achievable,” wrote study author Henry N. Lesser, MD, with the department of obstetrics and gynecology at Sinai Hospital in Baltimore, and colleagues.
The patients with planned cesarean delivery had a contraindication to vaginal delivery or otherwise chose to have a cesarean delivery. The researchers excluded from their analysis pregnancies with intrauterine fetal demise of either twin before labor or planned cesarean delivery.
The study’s reliance on data from a single practice decreases its external validity, the researchers noted. Induction of labor at this center typically occurs at 37 weeks’ gestation for monochorionic twins and at 38 weeks for dichorionic twins, and “senior personnel experienced in intrauterine twin manipulation are always present at delivery,” the study authors said.
The study describes “the experience of a single site with skilled obstetricians following a standardized approach to management of diamniotic twin deliveries,” Dr. Krishna said. “Findings may not be generalizable to many U.S. practices as obstetrics and gynecology residents often lack training in breech extraction or internal podalic version of the second twin. This underscores the importance of a concerted effort by skilled senior physicians to train junior physicians in vaginal delivery of the second twin to improve overall outcomes amongst women with diamniotic twin gestations.”
Michael F. Greene, MD, professor emeritus of obstetrics, gynecology, and reproductive biology at Massachusetts General Hospital, Boston, agreed that the findings are not generalizable to the national population. Approximately 10% of the patients in the study had prepregnancy obesity, whereas doctors practicing in other areas likely encounter higher rates, Dr. Greene said in an interview.
He also wondered about other data points that could be of interest but were not reported, such as the racial or ethnic distribution of the patients, rates of birth defects, the use of instruments to aid delivery, and neonatal outcomes for the dichorionic twins.
Monochorionic pregnancies entail a risk of twin-twin transfusion syndrome and other complications, including an increased likelihood of birth defects.
Dr. Greene is an associate editor with the New England Journal of Medicine, which in 2013 published results from the Twin Birth Study, an international trial where women with dichorionic or monochorionic twins were randomly assigned to planned vaginal delivery or planned cesarean delivery. Outcomes did not significantly differ between groups. In the trial, the rate of cesarean delivery in the group with planned vaginal delivery was 43.8%, and Dr. Greene discussed the implications of the study in an accompanying editorial.
Since then, the obstetrics and gynecology community “has been focusing in recent years on trying to avoid the first cesarean section” when it is safe to do so, Dr. Greene said. “That has become almost a bumper sticker in modern obstetrics.”
And patients should know that it is an option, Dr. Krishna added.
“Women with monochorionic-diamniotic twins should be counseled that with an experienced obstetrician that an attempt at vaginal delivery is not associated with adverse neonatal outcomes when compared with planned cesarean delivery,” Dr. Krishna said.
A study coauthor disclosed serving on the speakers bureau for Natera and Hologic. Dr. Krishna is a member of the editorial advisory board for Ob.Gyn. News.