Twins in Demand Through IVF?
Despite some couples' desires, doctors counsel against trying for twins through in vitro fertilization.
Medical Risks of Multiple Births
Health experts -- including all the doctors interviewed for this story -- don't approve of trying for twins because it's a risky undertaking. Those risks include:
- Infant death: Twins are five times more likely than single-birth babies to die within a month of birth.
- Preterm birth: Twins and other multiples are much more likely than single babies to be born early. According to the CDC, 60% of all U.S. twins born in 2006 were born prematurely, compared to 11% of single babies. And 12% of twins were born very preterm (before 32 weeks of gestation), compared to about 2% of single babies.
- Low birth weight: Twins and other multiples are more likely than single babies to be born at a low birth weight. The CDC reports that about 58% of U.S. twins born in 2006 were born at low birth weight, compared to 6% of single babies. And 10% of twins were born at very low birth weight, compared to 1% of single babies.
- Birth defects including cerebral palsy are more common in babies born prematurely.
- Risks to the mother: Women pregnant with more than one baby are at higher risk for preeclampsia, gestational diabetes, and bleeding before or after delivery, compared to women carrying one baby.
Of course, many twins are born on time and are healthy.
For instance, while the infant death rate among twins is much higher than the rate for single babies, the vast majority of infant twins don't die. CDC records show that about 30 out of 1,000 U.S. twins born in 2006 died during infancy, compared to six per 1,000 single babies.
So it's not that all twins are headed for complications. But their odds aren't as good as single babies.
"The good news is that most of the time with twins, and maybe even with triplets, people end up with normal, healthy babies. But there are significant number of bad outcomes," says Peaceman.
And those bad outcomes become more common with increasing numbers of babies. So twins are riskier than single babies, but less risky than triplets, quadruplets, or more.
Because of the relative risks, most doctors discourage trying for twins or other multiples.
"Anybody who comes in asking for multiple births, we will dissuade and try to get them thinking correctly," Perloe says. Muasher says he tells his patients that "the best outcome that I would like to hope for is to have one healthy baby."
Doctors can't guarantee twins at the onset of IVF, anyway. SART and the American Society of Reproductive Medicine (ASRM) have guidelines about how many embryos should be transferred to an IVF patient, based on her age, reproductive history, and embryo quality. But not all embryos that are transferred result in live births, and even if only one embryo is transferred, that embryo could split, leading to twins.