In-vitro fertilization (IVF) has come a long way since the first “test-tube” baby in 1978. Even so, there is still a lot of argument about the number of embryos to transfer into the woman’s uterus. What number of embryos is safe? What number is effective?

And even, what number is sane? (Octomom, anyone?)

Many couples using IVF prefer transferring multiple embryos to increase their chance for having at least one baby. However, there has been concern that transferring more than one embryo also creates a higher risk for complications for the baby or babies, including low birth weight and/or premature birth—even if only one baby is born.

Now, there is new research from the UK that tries to come up with some answers—and I think anyone considering IVF should know what these scientists have found.


The researchers, whose study was published in The Lancet this past January, investigated 124,148 IVF cycles involving the transfer of one, two or three embryos. They wanted to assess the benefit (having a live birth) versus the risks (preterm birth and low birth weight) to see which number of transfers might yield the best balance of safety and effectiveness. The women ranged in age from 18 to 50. Results…

The benefits. The study found that the odds of having a live birth were higher in women who received two embryos rather than in those who received one embryo. Women under age 40 were about twice as likely to have a live birth when receiving two embryos rather than one. And women over 40 were about three times as likely to have a live birth when receiving two embryos, rather than one.

But, interestingly, transferring three embryos did not further increase the chances of a live birth. In women 40 or older, their odds when receiving three embryos were the same as they were when receiving two embryos. And among women under age 40, their odds of live birth actually dropped by about 22% when they received three embryos instead of two.

No matter the woman’s age, multiple embryos increased the risk for preterm birth and low birth weight for the baby. Transferring two embryos versus one was associated with increased risks. Women under 40 receiving two embryos versus one were 2.25 times as likely to have a preterm birth and about three times as likely to have a low-birth-weight baby. Women over 40 receiving two embryos versus one were 25% as likely to have a preterm birth and approximately 50% more likely to have a low-birth-weight baby. Transferring three embryos increased these risks even more.

Since transferring three embryos did not seem to increase the chance of a live birth and did increase the risk for complications, the study authors advised that women of any age should not have more than two embryos transferred.

The question of two embryos versus one embryo wasn’t so easy to settle, of course, since transferring two brought better odds for a birth and worse odds for complications. The researchers concluded that this decision should be left up to couples and their clinicians.


Armed with these results, I called Norbert Gleicher, MD, founder, medical director and chief scientist of the Center for Human Reproduction in New York City, one of the oldest fertility clinics in the country. He had a different take on the issue. Dr. Gleicher is adamant that most women under 40 who are undergoing IVF should transfer at least two embryos…and that in women 40 or older, the number should usually be three or even, on rare occasions, four.

Dr. Gleicher’s reasoning is that most couples seeking IVF who are younger than age 40 want to have two children. This means that they have two options, he said. They can have two embryos transferred at once, in the hope of achieving two live births from one IVF cycle, in which case they would never need to use IVF again…or they can opt for a single transfer and, if it results in a live birth, they can have additional rounds of IVF in the future to try to produce a second child.

His point is, when you compare two single-embryo transfers to one double-embryo transfer, the risks aren’t that much more extreme for a double-embryo transfer. For example, if you’re under 40 and you want to have two children and you opt for two single-embryo transfers, you have twice the risk for premature delivery and twice the risk for low birth weight, compared with transferring one embryo once. If you opt for the transfer of two embryos at once, you’re 2.25 times as likely to have a preterm birth and three times as likely to have low birth weight, compared with transferring one embryo once.

Plus, IVF is physically difficult, time-consuming, emotionally draining and expensive, with typical costs of $25,000 or more per cycle that insurance does not always cover. In light of all this, Dr. Gleicher recommends the transfer of one embryo only if the mother is under 40 and specifically does not want two children.

The situation is different for older women, though, for two main reasons. With their older eggs, IVF is less likely to lead to fertilization and live birth…and women over 40 typically don’t want more than one child. In these women, in Dr. Gleicher’s view, transferring three embryos typically achieves the best balance between effectiveness and risk. But there is another wrinkle—if the couple is using donor eggs from a young woman, which increases the chance of a live birth substantially, Dr. Gleicher typically recommends transferring only one embryo to avoid the possibility that an older couple will be faced with carrying twins through a high-risk pregnancy and then having to raise twins.


So the UK study advises one or two embryos at a time, while this US expert recommends two to three or, rarely, four embryos depending on the circumstances and maternal age…so what’s a couple to do? There isn’t a clear consensus on the topic, so if you’re considering IVF, it’s important to discuss with your doctor all the risks and benefits. And, as with many medical conundrums, it never hurts to get a second—or even a third—opinion.