Labor takes longer in women pregnant with twins, a new study shows, suggesting that these mothers and their doctors could wait a few more hours before opting for cesarean delivery.
Using a national database of labor and delivery information from several clinical centers, the researchers found that twins required about one to three hours more than single babies to complete the first stage of labor. During this first stage, the cervix opens until it is wide enough for the baby to pass through; the second stage of birth is the actual delivery of the baby.
"Our data supports the suspected findings that labor progression of twin gestation is prolonged, compared to a singleton gestation," said study researcher Dr. Heidi Leftwich, a maternal-fetal medicine fellow at the University of Illinois at Chicago. "Doctors could let twins labor longer before calling it 'failure to progress.'"
The researchers compared about 900 twin pregnancies with 100,500 singleton pregnancies that served as controls. [9 Conditions That Pregnancy May Bring]
The researchers measured the time it took for women's cervixes to dilate 1 centimeter as a gauge for labor progression, and adjusted the results for confounding factors such as weight of the baby, mother's age and weight, and whether this was her first time giving birth.
In twin pregnancies, it took an average of 12.7 hours for the cervix to progress from 4 centimeters to fully dilated, at 10 centimeters. In singleton pregnancies, this took an average of 9.6 hours.
"Women who are pregnant with twins should anticipate that their labor may take longer than if they had a singleton gestation," Leftwich said.
In deciding whether to recommend a cesarean delivery, physicians look at how a woman's labor is progressing using a tool called the "Friedman labor curve." The curve shows the average time it takes for a woman to progress to 10 centimeters of cervical dilation and deliver the baby, and allows doctors to determine whether a patient is having a normal labor pattern.
This labor curve, however, may be outdated. It was devised in the 1950s and experts say it may not be a good estimate for the contemporary population. Today, both women and newborns are heavier on average compared to past decades, and more women use epidurals for pain relief. Such factors may affect labor progression.
Moreover, labor progress in twin gestations was not addressed in Friedman’s original work in developing the curve.
The researchers also found twins weighed on average 1.7 pounds (800 grams) less than singletons. Women with twins were more often older, and were more likely to deliver preterm. Twin gestations were almost twice as likely to have cesarean births.
It is not entirely known why twin labors take longer. One hypothesis that an overextended uterus may not function quite as well as it does in a singleton pregnancy, Leftwich said.
There are other reasons that a C-section may be recommended; for example, one or both twins may be out of position.
"The decision for a cesarean delivery shouldn't be only based on the strict definition of labor progression," Leftwich said.