Multiple Options

Globe-spanning trial settles question of which method of delivery is best for twins and expectant moms

Twin boys Eliyahu and Mordechai were delivered by Dr. Jon Barrett on Jan. 30, 2013 at Sunnybrook.

Photo: submitted by family

Since the early 1990s, the success of in vitro fertilization (IVF) and other assisted reproductive technologies such as intrauterine insemination and ovulation-stimulating drugs has contributed to a dramatic increase in multiple births worldwide. In Canada, there were about 8,000 twin births in 1993; now, that number is about 12,000.

A question that remains unanswered, however, is: which is the safest way to deliver twins—vaginal birth or planned caesarean section (C-section)?

For eight years, Dr. Jon Barrett, director of the Women & Babies Research Program at Sunnybrook Research Institute (SRI), has led the Twin Birth Study, an international, multicentre trial, in a quest to answer this question.

“Studies up to this date have been very unclear as to the best method of delivery for the optimal outcome for the babies and the mother. Many studies were suggesting that caesarean section might be a better option for the second twin, [who] is more at risk,” says Barrett, who is also chief of maternal-fetal medicine at Sunnybrook Health Sciences Centre. “But we also have years of history and experience where some studies suggest that a vaginal birth was safer.”

Women carrying twins or multiples—triplets, quadruplets and quintuplets—are at increased risk of maternal illnesses such as gestational diabetes and high blood pressure, for which specialized care is required. Each year, 3,800 infants are born at Sunnybrook. Of these, more than 300 are multiple births and considered high-risk deliveries. Twin pregnancies complicate 2% to 3% of all births in many countries. They are also associated with higher rates of premature birth, low birth weight, newborn death and growth abnormalities than are single births.

Through an $8.6-million grant, Barrett and researchers at SRI’s Centre for Mother, Infant and Child Research coordinated the largest randomized controlled trial for twin births ever done. They looked at 2,804 women who delivered twins at 106 hospitals in 25 countries between 2003 and 2011. Sunnybrook recruited 84 patients, the largest group among all of the centres in Canada.

Dr. Jon Barrett examines Kelly Newcombe, who is pregnant with twins. Barrett led an international study on twin births.

Photo: Doug Nicholson

The trial was designed to determine which method of planned delivery—vaginal birth or C-section—increased the risk of illness and death in women giving birth to twins between 32 and 38 weeks gestation with the first twin positioned head down. Women were randomly allocated to each group; 89.9% delivered twins by C-section, and 56.2% delivered twins vaginally.

Although public perception is that C-section is safer due to reduced risks associated with vaginal birth, such as birth asphyxia and trauma, Barrett found no benefits to justify either method as superior.

“The results show that planned vaginal birth seems to be as safe as a planned caesarean section for the babies,” says Barrett, who is also an associate professor in obstetrics and gynecology at the University of Toronto.

He found that the infants were at an equal risk of severe illness or death in either delivery approach. Interestingly, the study showed that women in the planned C-section group delivered slightly earlier—common for twins—compared with those in the vaginal group. Moreover, the risk of death, serious illness or other significant adverse effects was the same for women in each group.


In some parts of the world, the incidence of multiple births is decreasing because of legislative laws controlling the number of embryos that are implanted in the uterus.

This is not so in North America, where multiple births continue to rise, with one exception.

In Canada, Québec is the only province that covers the cost of in vitro fertilization (IVF). In 2010, the Quebec government announced it would fund up to three rounds of IVF per couple. Funding would be contingent, however, on only one embryo being transferred at a time, to help reduce the number of multiple births. Twin births in the province decreased from 27.2% to 5.2% within the first six months of the funding program, according to the Canadian Fertility and Andrology Society.

“It seems that whilst planned vaginal birth was not better for the babies, a C-section was not much more dangerous for the mothers, but the babies in the planned C-section delivered earlier, which is not good [either],” Barrett says. “In addition, why would someone [choose to] have surgery if it was not better for the babies, and it would affect her next pregnancy?” It is common for women who have a C-section for the first delivery to not be able to have a vaginal birth for subsequent deliveries.

Barrett says he wasn’t surprised by the findings. “I’m delighted with the results because they fit in with my worldview of having babies. It’s always been my bias that vaginal birth is safe for twins because if you deliver twins in the right place with the right people, then it’s a safe procedure. We were very careful in the trial to make sure that those conditions were met.”

There has only been one other randomized controlled trial that compared both delivery methods. It looked at 60 pairs of twins between 35 and 42 weeks gestation. Results of that study were inconclusive due to its small sample size.

The study is timely. Barrett points out that with the rise in C-section birth rates for twins, vaginal delivery of twins could have one day become obsolete. “It was important to do this trial now because if we didn’t do it, then we would have lost the skills necessary to do vaginal births, and by default it would have gone to caesarean section,” he says.

Barrett and colleagues presented the results at the annual meeting of the Society for Maternal Fetal Medicine in February 2013, and have submitted a manuscript for publication in The New England Journal of Medicine.

To understand better the immediate and long-term outcomes of the Twin Birth Study, the team is conducting a two-year follow-up of the women and infants. They will look for developmental delay, cerebral palsy and other significant abnormalities in the infants at two years of age, as well as the effect of delivery method on the mother.

“We also want to look at the longer-term impact of vaginal birth on the mother’s pelvic floor, [because] that’s an area with a lot of interesting risk for incontinence,” Barrett says.

The study was a massive effort that involved a large team of people to organize and collect data over the years from all of the centres. It lagged about two years behind schedule, because it was a challenge to recruit pregnant women with twins due to societal pressures surrounding C-section and vaginal deliveries. Barrett describes the journey as a humbling experience he was glad to be a part of as principal investigator. “We are very grateful to all the patients and doctors who participated in the trial,” he says with a smile.

The Twin Birth Study is the first of its kind to provide reliable evidence that may change obstetrical practices, says Barrett. He encourages physicians and patients to read the results of the study and reconsider the options available for delivering twins.

His advice to expectant mothers: “[Unless] there is another reason they should have a caesarean section, then they should plan for a vaginal birth because the study shows it’s as safe as a C-section without the surgery, and it allows the pregnancy to proceed a little bit longer.”

— Eleni Kanavas

Barrett’s research was funded by the Canadian Institutes of Health Research.