WEDNESDAY, Dec. 22 (HealthDay News) -- Women who undergo in-vitro fertilization (IVF) are almost five times more likely to give birth to a single healthy baby following the implantation of a single embryo than are women who choose to have two embryos implanted at the same time, an international team of experts has found.

The finding comes from an analysis of data involving nearly 1,400 women who participated in one of eight different embryo transfer studies. Approximately half of the women underwent procedures involving the single transfer of an embryo, while the other half underwent a double embryo procedure.

Overall, the study authors noted that, relative to a double embryo transfer, a single embryo transfer appears to significantly increase the chances of carrying a baby to a full term of more than 37 weeks.

In addition to lowering the risk for premature birth, a single embryo transfer also appeared to lower the risk for delivering a low birth weight baby, D.J. McLernon, a research fellow with the medical statistics team in the section of population health at the University of Aberdeen in the United Kingdom, and colleagues reported in the Dec. 22 online edition of BMJ.

"Our review should be useful in informing decision making regarding the number of embryos to transfer in IVF," the authors wrote in their report. They added that their observations could offer practical guidance to would-be mothers and doctors who are eager to foster optimal conditions for a successful pregnancy, while at the same time hoping to avoid the increased health risks associated with IVF procedures that give rise to multiple-birth pregnancies.

The authors concluded that doctors should advise patients to choose the single embryo transfer option over what appears to be the less optimal double embryo transfer option.

At face value, the data seemed to suggest that the double embryo transfer option does, in fact, offer the mother much better odds for giving birth to a single healthy baby. While among study participants just 27 percent of single embryo transfer procedures resulted in the birth of a healthy baby, that figure rose to 42 percent of double embryo transfer births, the investigators found.

However, that spread was narrowed considerably when the authors focused on those women undergoing an initial single embryo transfer procedure who then underwent a second single implant (of a frozen embryo). That scenario (in which, in essence, two single embryo transfers are conducted in sequence) prompted a 38 percent success rate -- a figure just 4 percent shy of the 42 percent success rate attributed to two embryos being implanted simultaneously.

What's more, the researchers further found that a single embryo transfer offered women an 87 percent better chance of carrying a baby to full-term than a double embryo transfer.

In addition, the single embryo transfer entailed just one-third of the risk (compared with the double embryo transfer procedure) that the mother would ultimately deliver a low birth weight baby.

Commenting on the study, Dr. Laurel Stadtmauer, an associate professor of obstetrics and gynecology and IVF associate director of the Eastern Virginia Medical School Jones Institute for Reproductive Medicine in Norfolk, Va., described the current effort as "very convincing."

"There is a consensus that there is a high number of multiple births from IVF, and we're all doing everything we can to reduce that rate of birth because we know that premature birth and multiple births do lead to a higher risk for the babies and for the mother," she explained.

"And this certainly shows that cumulatively you can often achieve a much better outcome with two separate single embryo transfers compared with one double embryo transfer -- which would mean a much lower chance of a multiple pregnancy and all the related complications," Stadtmauer continued.

"However, while a single embryo transfer is appropriate for a number of women it's not appropriate in all women. Because while in young women or women with good prognostic factors a single embryo transfer can be very successful, in women over the age of 38 or women with low chances of pregnancy and poor prognostic factors, there would be a significant reduction in success compared to a double pregnancy transfer," she cautioned.

"There are also financial and emotional costs to undergoing a procedure twice, particularly as there is always a risk for failure. So not all women are easily convinced to choose the single transfer option," Stadtmauer added. "So while it's definitely the future, it's not for everybody. But the better we get at selecting which embryos have the highest chances of implanting, the better we can get at directing patients towards elective single embryo transfers."

More information

For more on in-vitro fertilization, visit the U.S. National Library of Medicine.