Infertility and Assisted Reproduction

IVF and Single Embryo Transfers

When reproductive medicine was in its infancy, many fertility clinics transferred multiple embryos during each cycle, attempting to increase the rate of pregnancy. This technique resulted in many twin, triple, and even higher-order multiple births. Unfortunately, multiple births—including twin births—greatly increase the chances that a woman and her children will have poor health outcomes.

The most common problems in the short term are that multiples are often preterm and the babies often have a low birth weight. Preemies are more likely to need intensive care and longer stays at the hospital and are at higher risk of dying shortly after birth. Birth impairments are also more common among multiples, although they affect a minority of the infants. The longer-term consequences of preterm delivery and low birth weight include developmental disabilities such as cerebral palsy (CP). Whereas the rate of CP is about 2 percent among singletons, some studies have found that the rate is about five times as high among twins and about twenty times as high among high-order multiples. These risks are not limited to multiple births: babies that are born singletons but were part of a multiple pregnancy have some of them as well. Multiple pregnancies also carry a higher risk of health complications for the mother during pregnancy and birth.

And there are effects on the health of the family as well: studies show that divorce is much more common among couples that have had multiples than among couples who have had singletons. Finally, there are consequences for society at large, because the costs of the medical care for multiple pregnancies and infants born in multiple births are huge compared to the costs associated with caring for singletons.

Because of these risks, many experts in the field now encourage the strategy of transferring only one embryo at a time. A 2010 meta-analysis of clinical trials comparing the outcomes of double embryo transfers with the outcomes of a sequence of one single-embryo transfer followed by a thawed embryo transfer if the first cycle has not succeeded found single-embryo transfer more likely to lead to the birth of a single, healthy baby.⁶ Though the first strategy—double-embryo transfer—leads to pregnancy faster, it is associated with multiple births and the related adverse health outcomes. The second strategy—single-embryo transfer— may require more attempts but almost invariably yields singleton births and better health outcomes for both mother and baby. The chance of a woman giving birth to a single full-term baby (over thirty-seven weeks) following single-embryo transfer is almost five times greater than her chance of doing so following double-embryo transfer.

The main barrier to elective singleembryo transfers is cost. Many families are unable to pay for multiple IVF cycles, so they opt to have multiple embryos transferred in a single cycle. The first insurance company to address this problem, Aetna, recently marketed a benefit that offers a free “rescue” IVF cycle to women who choose elective single-embryo transfer if the first cycle fails. 

Excerpted from the 2011 edition of Our Bodies, Ourselves. © 2011, Boston Women's Health Book Collective.

6. D. J. McLernon et al., “Clinical Effectiveness of Elective Single Versus Double Embryo Transfer: Meta-analysis of Individual Patient Data from Randomised Trials,” British Medical Journal 341 (December 21, 2010): c6945.