According to the most recent statistics, nearly 1 in every 31 pregnant women is expecting twins. That rate is about three times higher than it was in the 1950s, in part because women are having babies at older ages, and women over 35 naturally conceive more multiples. But most of the increase has been caused by fertility drugs and in vitro fertilization (IVF).
Carrying twins or higher-order multiples takes a toll on the mother, putting her at higher risk of nearly every pregnancy complication – preterm birth, hypertensive disorders including preeclampsia and eclampsia, anemia, gestational diabetes, placenta previa, and postpartum hemorrhage. Half of all twins have to be admitted to the neonatal intensive care unit, and an estimated 7 percent have lifelong disabilities due to prematurity. The rates are even higher for triplets; 95 percent are admitted to intensive care.
To prevent those risks, the Society for Reproductive Medicine recently adopted the recommendation that IVF patients under age 35 transfer only one embryo at a time. In elective single embryo transfer, doctors choose the most viable embryo and preserve the others. If the woman does not get pregnant, the remaining embryos are transferred, one at a time, in future months. That recommendation is based on growing evidence that in younger women who are more likely to get pregnant, transferring a single embryo reduces the risk of multiples without reducing pregnancy rates.
New evidence from Europe
A study published this month by researchers in Barcelona confirmed that single embryo transfer works. The researchers followed 628 couples who underwent IVF between 2002 and 2006. In total, 66 percent of couples who chose a single embryo each month got pregnant, compared to 70 percent of couples who chose to transfer two. Only 7 percent of couples who chose a single embryo had twins, compared to 27 percent of the couples who transferred two embryos at once.
In Quebec, it’s now the law
In 2010, Quebec became the first Canadian province to pay for IVF treatment for couples – up to three tries for women under the age of 42. But as part of the plan, the government passed a law saying that physicians should only transfer one embryo at a time. Doctors could choose to transfer more than one embryo in patients with a poor prognosis, but only if they provided justification. In the first three months that the law was enacted, the multiple pregnancy rate for IVF patients in Quebec dropped from 26 percent to less than 4 percent.
In a few countries, including Sweden and Australia, single embryo transfer is already the norm. But in the U.S., many women still choose two embryos. I’ll discuss the reasons for that – and some ways that experts hope to change couples’ decisions – in my next post.
Rodriguez DB et al. Elective single embryo transfer and cumulative pregnancy rate: five-year experience in a Southern European country. Gynecological Endocrinology, 2011. [epub ahead of print].
Bissonnette F et al. Working to eliminate multiple pregnancies: a success story in Quebec. Reprod Biomed Online. 2011, 23(4): 500-4.