New federal numbers show nearly half of all babies born with advanced fertility help are multiple births.
In the five years since the "Octomom" case — when a California woman gave birth to octuplets — big multiple births have decreased substantially, but the twin rate has barely budged.
Twins aren't always twice as nice; they have much higher risks of prematurity and serious health problems.
Now fertility experts are pushing a new goal and that is a growing number of couples attempting pregnancy with just a single embryo, helped by new ways to pick the ones most likely to succeed.
New guidelines are also urging doctors to stress this approach.
The Centres for Disease Control and Prevention's most recent numbers show that 46% of IVF babies are multiples — mostly twins — and 37% are born premature. By comparison, only 3% of babies born without fertility help are twins and about 12% are preterm.
It's mostly an American problem and some European countries that pay for fertility treatments require using one embryo at a time.
The American Society for Reproductive Medicine is trying to make it the norm in the US, too. Its guidelines, updated earlier this year, say that for women with reasonable medical odds of success, those under 35 should be offered a single embryo transfer and no more than two at a time. The number rises with age to two or three embryos for women up to 40, since older women have more trouble conceiving.
The medical director of Reproductive Medicine Associates of New York, a Manhattan fertility clinic, Dr Alan Copperman, said: “Our goal in 2014 is to minimize the birth of twins.
"This year I'm talking about two versus one. Several years ago I was talking about three versus two" embryos.”
The one-at-a-time idea is catching on. Only 4% of women under 35 used single embryos in 2007 but nearly 12% did in 2011.
It's less common among older women, who account for fewer IVF pregnancies, but it is gaining among them, too.
(Photo of twins from Shutterstock)