A study of the duration of the second stage of labor in more than 2,000 women who delivered twins may provide useful reference ranges for doctors and patients, researchers say.
Although the analysis found statistically significant differences in second-stage labor lengths for twin and singleton deliveries, “ultimately I think the value in this is seeing that it is not much different,” said Nathan Fox, MD, a maternal-fetal medicine specialist who has studied twin pregnancies and delivery of twins.
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While most twin births occur by cesarean delivery, vaginal delivery is a preferred method for diamniotic twins with the first twin in vertex presentation, wrote study author Gabriel Levin, MD, and colleagues. Prior studies, however, have not clearly established the duration of the second stage of labor in twin deliveries – that is, the time from 10-cm dilation until delivery of the first twin, they said.
Knowing “the parameters of the normal second stage of labor” for twin deliveries may help guide clinical practice and possibly avoid unnecessary operative deliveries, the researchers wrote.
To establish normal ranges for the second stage of labor in twin deliveries, Levin, of the department of obstetrics and gynecology at Hadassah-Hebrew University Medical Center, Jerusalem, and coauthors conducted a retrospective cohort study. They analyzed data from three large academic hospitals in Israel between 2011 and June 2020 and assessed the length of the second stage of labor by obstetric history and clinical characteristics.
The researchers included data from women who delivered the first of diamniotic twins spontaneously or delivered a singleton spontaneously. The researchers excluded twin pregnancies with fetal demise of one or both twins, structural anomaly or chromosomal abnormality, monochorionic complications, and first twin in a nonvertex presentation. They did not consider the delivery mode of the second twin.
The study included 2,009 twin deliveries and 135,217 singleton deliveries. Of the women with twin deliveries, 32.6% were nulliparous (that is, no previous vaginal deliveries), 61.5% were parous (one to four previous vaginal deliveries, and no cesarean deliveries), and 5.9% were grand multiparous (at least five previous deliveries).
Of the women with singleton deliveries, 29% were nulliparous.
For nulliparous women delivering twins, the median length of the second stage was 1 hour 27 minutes (interquartile range, 40-147 minutes), and the 95th percentile was 3 hours 51 minutes.
For parous women delivering twins, the median length of the second stage was 18 minutes (interquartile range, 8-36 minutes), and the 95th percentile was 1 hour 56 minutes.
For grand multiparous women, the median length of the second stage was 10 minutes.
In a multivariable analysis, epidural anesthesia and induction of labor were independently associated with increased length of the second stage of labor.
Second-stage labor longer than the 95th percentile based on parity and epidural status was associated with approximately twice the risk of admission to the neonatal intensive care unit (35.4% vs. 16.4%) and need for phototherapy, the researchers reported.
Compared with singleton deliveries, the second stage was longer in twin deliveries. Among nulliparous patients, the median length of the second stage of labor was 1 hour 18 minutes for singleton deliveries, versus 1 hour 30 minutes for twin deliveries. Among parous patients, the median length of the second stage was 19 minutes for twin deliveries, compared with 10 minutes for singleton deliveries.
The study was conducted in Israel, which may limit its generalizability, the authors noted. In addition, the researchers lacked data about maternal morbidity and had limited data about neonatal morbidity. “The exact time that the woman became 10-cm dilated cannot be known, a problem inherent to all such studies,” and cases where doctors artificially ended labor with operative delivery were not included, the researchers added. “More research is needed to determine at what point, if any, intervention is warranted to shorten the second stage in patients delivering twins,” Levin and colleagues wrote.
Providing a Framework
“We always get more concerned if the labor process is happening in a way that is unusual,” and this study provides data that can provide a framework for that thought process, said Fox, who was not involved in the study.
The results demonstrate that the second stage of labor for twin deliveries may take a long time and “that is not necessarily a bad thing,” said Fox, clinical professor of obstetrics and gynecology and maternal and fetal medicine at the Icahn School of Medicine at Mount Sinai in New York.
For women having their first child, the second stage of labor tends to take much longer than it does for women who have had children. “That is well known for singletons, and everyone assumes it is the same for twins,” but this study quantifies the durations for twins, he said. “That is valuable, and it is also helpful for women to know what to expect.”
A study coauthor disclosed financial ties to PregnanTech and Anthem AI, and money paid to their institution from New Sight. Fox works at Maternal Fetal Medicine Associates and Carnegie Imaging for Women in New York and is the creator and host of the Healthful Woman Podcast. He had no relevant financial disclosures.