Many of the twins delivered via cesarean section could have been safely delivered the old-fashioned way, according to a new study in the New England Journal of Medicine.
Twin births have been on the rise for three decades, fueled mainly by use of fertility treatments. The increase in pregnancies among women over the age of 30 is also a factor, since the odds of twins increase with maternal age. In the United States alone, the rate of twin births is up 76% since 1980, according to data from the Centers for Disease Control and Prevention.
Several studies have found that birth by cesarean section reduces the risk of complications for one or both twins compared with a vaginal delivery. The results seemed to fuel a shift toward C-sections for twins, in the U.S. and elsewhere. (One study of U.S. births found that 75% of twins were delivered by C-section in 2008, up from 54% in 1995.)
But none of these studies was a randomized clinical trial, the type that's considered the gold standard of medical research. So an international group of researchers launched the Twin Birth Study, which ultimately included 106 medical centers in 25 countries. As noted by an editorial that accompanies the New England Journal of Medicine report, it took the researchers 7.5 years to recruit nearly 3,000 mothers to participate in the study.
Overall, 1,392 women were randomly assigned to have a planned cesarean section, and 1,406 were randomly assigned to plan for a vaginal delivery, though they could switch to a C-section for one or both babies if that became medically necessary.
As expected, women in the cesarean group were more likely to be able to stick with their original plan: 90% of them did deliver both of their twins via C-section. (The others delivered one or both twins vaginally.) Meanwhile, 56% of the women who had been planning for a vaginal delivery were able to stick with their plan; another 40% of these women wound up delivering both babies by C-section and 4% delivered one each way.
The main focus of the study was to see whether mothers and babies in one group or the other were more likely to have medical problems during childbirth or in the first four weeks afterward. For the infants, such adverse events could include a birth trauma like a skull fracture or spinal cord injury, the need for oxygen or a breathing tube, or a low Apgar score. For mothers, problems included death, hemorrhage, blood clot or a serious infection.
The risk of these problems turned out to be the same for mothers and babies in both groups. The rate of adverse events was 2.2% for infants in the planned C-section group and 1.9% for infants in the planned vaginal delivery group, according to the study. That difference wasn't statistically significant.
Second-born twins were 90% more likely than first-born twins to have a medical issue, but that was true whether they were in the C-section or the vaginal delivery group.
Among the mothers, 7.3% of those who were planning to have a C-section had some sort of medical problem, along with 8.5% who were planning to have a vaginal delivery. That difference wasn't statistically significant either.
One difference the researchers did find was that babies in the planned C-section group were born at an earlier gestational age than babies in the planned vaginal delivery group, though the difference amounted to less than one day, on average.
So women expecting twins who would like to try for a vaginal delivery can do so safely -- but only under the conditions in the trial, the researchers wrote. Women were attended by an experienced obstetrician, and they delivered in facilities that could perform an emergency C-section within 30 minutes, if that became necessary.
Although the findings make clear that vaginal delivery of twins is safe when performed by skilled hands, it probably won't persuade many women to plan for it, Dr. Michael F. Greene, chief of obstetrics at Massachusetts General Hospital in Boston, wrote in the editorial. C-sections are too much in vogue, and babies who are in a breech position are rarely delivered vaginally, among other reasons.
"It seems unlikely that we will see a major change in use of cesarean delivery for twins nationwide," he concluded.