Dr. Robert Stillman is used to a common plea from infertile couples: that he transfer multiple embryos to increase their chances of getting pregnant.
Some women even yell and scream at him, he said, begging for twins.
"The Holy Grail is one embryo, but I have patients every day asking for more, including twice today," said Stillman, a reproductive endocrinologist at Shady Grove Fertility Center in Washington, D.C. "They say they don't want to pay for another cycle or to go through all this again."
An in vitro fertilization (IVF) cycle of only two embryos produces a 60 percent chance of twins, putting babies at risk for premature birth and lifelong health problems.
"Even when you show them the data, they still ask for it," he said. "It's an enormous issue and it keeps the frequency of multiple pregnancies high."
IVF is among the biggest success stories of modern medicine -- its founders just won the Nobel Prize -- but multiple pregnancies put financial strain on an already over-burdened health care system.
Even with new guidelines to transfer one embryo for each in vitro cycle, doctors come under enormous pressure to accommodate couples' demands.
Dr. Michael Kamrava, the Beverly Hills fertility doctor who assisted octomom Nadya Suleman, admitted last week, for instance, that he had made a mistake in 2008 by transferring a dozen embryos against his better judgment.
Kamrava, who helped Suleman conceive six other children before the octuplets, testified in tears before a Medical Board of California hearing last week, according to the Los Angeles Times.
"I'm sorry for what happened," he said. "When I look back at it, I wish I had never done it and it will never happen again."
His attorney, Henry Fenton, asked, "Do you feel that what you did was wrong?"
"At the time that I did it, I thought I did the right thing," said Kamrava, who could lose his medical license. "When I look back at it, even with all those circumstances, I was wrong."
When Kamrava recommended implanting four embryos, or using Suleman's previously frozen embryos, she was adamant he transfer more.
"I had to go with the patient," he testified.
According to the Centers for Disease Control and Prevention, 142,435 assisted reproductive technology cycles were performed at 430 reporting clinics in the United States in 2006, resulting in 43,412 live births (deliveries of one or more living infants) and 57,569 infants.
The incidence of twins has jumped 65 percent in the past two decades. A record 138,961 twin births -- 32.2 per 1,000 live births -- were recorded in 2007, according to the CDC's vital statistics. In addition, there were 5,968 triplet births, 369 quadruplets and 91 quintuplets or higher.
Since then, there has been a reduction in the number of triplets and quadruplets, although the rate of twins has stayed stable, Stillman said.
"Who is to decide how many embryos is enough?" he asked. "If I take a stand and transfer one embryo and they want two, and I talk them into one and they don't get pregnant, it's my fault. There isn't just the blame, but I feel badly."
Shady Grove is the biggest fertility center in the United States, handling 4,200 cycles a year. In certain patient groups, the singleton success rate is about the same as using two embryos. "That's the amazing thing," Stillman said.