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.
The main problem, however, is that for each new frozen transfer, she must wait three to eight more weeks, take more estrogen and progesterone supplements to thicken the lining of her uterus (to help embryos implant) and pay $2,500 to $4,500 in addition to the cost of the first cycle, which ranges from $12,000 to $15,000 without insurance coverage. (It's worth mentioning that some doctors offer package pricing.) That's not to mention the angst factor. If a woman has been trying for years to get pregnant, the last thing she wants to hear is another, "You have a negative pregnancy result" any more times than she has to.
The typical IVF patient doesn't want to waste any time getting pregnant, and she usually wants more than one child, explains Norbert Gleicher, medical director at the Center for Human Reproduction in New York City. "The majority of my patients want twins," he says. "The older they are, the more they want them. And the longer they've been trying to get pregnant, the more they want them."
Yet the increasing number of doctors who advocate single embryo transfers say their goal is to avoid unnecessarily risky twin pregnancies, which account for 16 to 33 percent of IVF pregnancies, according to 2009 figures from the Society for Assisted Reproductive Technology. (By contrast, triplet IVF pregnancies, which are particularly dangerous, make up 1.5 percent of IFV pregnancies. The chances of conceiving twins naturally is about 1 in 89 pregnancies.) These doctors tend to point out that mothers carrying twins suffer from more hypertension, gestational diabetes, heart stress, and placental problems than those pregnant with singletons, and twin babies have higher rates of severe premature birth, handicaps, low birth weight, and infant mortality.
Those risks would make twins seem like a terrible idea, if they applied to IVF patients, and Gleicher insists that they don't.
He says that IVF patients actually contend with a much lower set of risks than do other mothers of multiples, since they're closely monitored and managed from the moment of conception. Twin mothers in the general population, by contrast, might not know they are having twins until later in their pregnancies and don't receive proper prenatal care. Gleicher recently co-authored a paper in Fertility and Sterility arguing that undergoing two singleton pregnancies carries as much risk as one twin pregnancy.
Finally, fertility doctors shouldn't dissuade a patient from trying for twins for the simple reason that they can't guarantee she will be able to get pregnant a second time, when she will be that much older. For many patients short on time and money, twins are a blessing. Current guidelines give women a good chance of getting them without incurring a high risk of getting pregnant with more than two. If that approach allows more women to get pregnant at all than from doling out embryos one by one, it's not worth fixing a system that appears to be working just fine.