IVF does carry major risks, which include premature birth, low birth weight, stillbirth, spontaneous abortion, preeclampsia, placenta previa, and, to a lesser extent, birth defects and cerebral palsy.
What is responsible for these poor outcomes? To find out, Alastair G. Sutcliffe, MD, of the Institute of Child Health at the University College London, and Michael Ludwig, MD, of the Center for Hormonal and Metabolic Illnesses in Hamburg, Germany, analyzed 30 years of data on IVF.
The main finding: Most IVF risks are due to multiple births, and not to the IVF procedure itself. Twins, triplets, and other multiple-birth children are at much higher risk of premature or low birth weight than are singleton children. And premature birth and low birth weight are linked to a host of health risks.
But even single children born via IVF have more health risks than do naturally conceived children. Nearly all these risks, the researchers find, are due to the same parental factors -- such as older age or genetic defects -- that make it difficult for a couple to conceive naturally.
"The things related to subfertility are probably the factors that result in the subtle differences in children born via assisted reproduction technology and children naturally conceived," Sutcliffe tells WebMD.
The findings closely mirror those of an expert panel convened in 2005 by the U.S. National Institute of Child Health and Human Development. NICHD medical officer Uma M. Reddy, MD, MPH, was lead author of the panel's report.
"The majority of problems we see with assisted reproductive technology are multiple births," Reddy tells WebMD. "But even singletons have higher risk of complications. But is it due to the procedure or to factors related to infertility? More and more evidence suggests it is not due to the procedure."
In vitro fertilization doctors agree with this assessment, says George Attia, MD, director of reproductive endocrinology and infertility at the University of Miami Miller School of Medicine.
"Most of the risks don't arise from the technique, but from the background biology of the couple," Attia tells WebMD. "Dr. Sutcliffe is right on the spot."
Single-Embryo Transfer: Answer to IVF Risk?
In the U.S., doctors typically implant two or more embryos, which greatly increases the chance of multiple births -- and greatly increases pregnancy risk.
"The majority of the patients want three or four embryos to be transferred," Attia says. "In the U.S., there is a different mentality. Most of this is not covered by insurance, so they really want to get pregnant on the first try and not have to do this several times. In Europe, where IVF is mostly covered by national health services, there is much more stress on single-embryo transfer."
Sutcliffe says that European doctors achieve nearly the same success rate with single-embryo transfers as with multiple-embryo transfers. Given the vastly reduced risk of multiple births, he suggests that U.S. doctors should look to Europe for guidance.
"My research, and that of many others in the field, suggests that if IVF babies are not born prematurely, they really have virtually the same prospects as a naturally conceived child," Sutcliffe says. "Especially in the U.S., the main risk is due to the fact that people are putting in too many embryos. As a result, you can have twins, triplets, quadruplets, or more and expose yourself and your babies to the risk of premature birth."
"Definitely single-embryo transfer is much better," Reddy says. "The problem is that for older women, you have to balance out the cost and the number of procedures. For a woman over 40, it is gong to take many more cycles. But we in the U.S. are trying to increase the amount of single-embryo transfers and decrease the number of multiple-embryo transfers."
Indeed, the American Society for Reproductive Medicine's June 2006 guidelines suggest that doctors transfer only a single embryo for women under age 35 with good prospects for success. For women under age 38, they recommend transfer of no more than two embryos. But for older women or women with poorer prospects for successful pregnancy, the ASRM leaves the door open for transfer of up to five embryos.
Attia says his institution does not transfer more than two embryos per procedure. He and Reddy each note that twin births do not appear to be as risky as higher-multiple births. Both join Sutcliffe in calling for more research.