In the two years since 33-year-old Nadya Suleman gave birth to octuplets after being implanted with a dozen embryos, the field of fertility medicine has done a pretty good job of reassuring the public that this will never happen again. Not only did the California medical board revoke her doctor's license this summer, the American Society for Reproductive Medicine has tightened its guidelines on how many embryos can be placed inside a patient's uterus during an in-vitro fertilization cycle—ranging from one to two for women under 35 to three to five for women in their early 40s.
However, there's growing enthusiasm among reproductive specialists for an even more extreme approach: limiting that number to just one embryo. Except in cases in which the embryo divides in utero, the method is an effective way to guarantee IVF patients who are dead set against having multiples they won't be shopping for one of those sidewalk-wide strollers. Or in rare circumstances, it also prevents these parents of IVF twins from having to wrestle with the ethical dilemma of terminating one of their fetuses—like the couples described in a recent New York Times Magazine article.
While "single embryo transfer" is a welcome treatment option for patients who want one baby at a time, there are still good reasons to keep the old method of throwing a bunch of embryos into a uterus and seeing what sticks, particularly for women who want to get pregnant as quickly and cheaply as possible.
The most obvious is that despite recent reports of promising pregnancy rates, an IVF patient's chances of conceiving when only one embryo is transferred are simply not as high as when more embryos are transferred, according to the results of a study published last month in Reproductive BioMedicine Online. Doctors at five Quebec fertility clinics performed 1,353 IVF cycles on patients ranging from 22 to 46 years old, with an average age of 37. They transferred one embryo in half the cases and two or more in the rest. The clinical pregnancy rate was 32 percent for the single transfer group compared with 42 percent for the other method. That's a significant difference in a field in which doctors covet every percentage point and patients have thousands of dollars on the line—and, in many cases, little time to waste.
IVF is largely a numbers games. The more embryos doctors put back in you, the better chance you have of one implanting and growing into a baby. The exception is if you are under 35 and have embryos that are so robust they practically leap from the incubator to the uterus on their own. In fact, a recent study from the journal Fertility and Sterility found that these "dream patients" had just as good of a chance of becoming pregnant with one embryo as two. However, the majority of IVF patients are older. The quality of their eggs—and thus embryos—likely has declined with age, so they benefit from volume.
That reality alone would seem to kill the buzz over single embryo transfers. But the authors of an important Finnish study say the method can be effective in patients even as old as 40— if they undergo a couple cycles in a row. Here's how it works: A woman takes drugs to stimulate her ovaries to release anywhere from five to 20 eggs. They are surgically retrieved, fertilized and grown in an incubator. The doctor transfers the best embryo to her womb and freezes the rest. So if the first transfer fails, the patient can dip into her frozen supply. But unlike a normal IVF cycle in which doctors will transfer several at a time, doctors practicing single embryo transfer will dole them out piecemeal.