"IVF is the most regulated medical specialty in the U.S.," said Grazi. "Every IVF center in the U.S. has to report every IVF and its outcome to the Centers for Disease Control and Prevention."
That means that if a patient gets pregnant on the second cycle, it's only a 50 percent success rate. Those percentages, said Grazi, mean a lot to doctors and patients, who can look at the numbers on the Internet. If double embryo transplants are going to result in more pregnancies, then doctors and patients may be more inclined to choose them.
But doctors say they do their best to emphasize the benefits of single embryo transfer, though it's difficult to convince patients of the benefits. Cost is one of the biggest factors. In vitro fertilization procedures can cost thousands of dollars, and medical insurance does not often cover them.
"It is cheaper for patients to do one transfer procedure than to do two transfer procedures," said Dr. Rick Paulson, professor of obstetrics and gynecology at the University of Southern California's Keck School of Medicine in Los Angeles. "Until we have universal medical insurance that pays for infertility treatment, this factor is always going to be important."
"Patients think 'two for the price of one,'" said Dr. Steven Lindheim, professor of obstetrics and gynecology at the University of Cincinnati College of Medicine's Center for Reproductive Health.
Even though the study showed a fresh single embryo transfer followed by a frozen embryo transfer can lead to a live birth, it's still a second procedure and as a result, an additional cost.
And although multiple births can be medically dangerous for mothers and children, many women actually want twins.
"Many patients, especially older ones, consider twins a good outcome," said Paulson. "They know that if they are having fertility treatment at the age of 40, having twins means not having to worry about coming back for fertility treatment when they are 42, and when success rates will be even lower."
Older women are also not the best candidates for single embryo transfers, Grazi said. Their embryos are less likely to be viable, and older women are also far less likely to have multiple births, so the complications linked to multiple births aren't relevant to them.
While it's illegal in some European countries to transfer more than one embryo, doctors say that type of regulation would never catch on in the U.S. In addition to the financial pressures of infertility, it's also psychologically devastating.
"When you've been struggling with this devastating situation for years and sometimes even decades, it's probably best not to second-guess the decisions these couples make," said Grazi.