(RxWiki News) One consideration in undergoing in vitro fertilization (IVF) treatment to have a baby is how many embryos to transfer into a woman's womb at once. One? Two? Three?
The results of a large study from Australia and New Zealand point to data revealing that the rate of multiples (twins, triplets, etc.) and the mortality rate of babies during or just after birth are lower when just a single embryo is transferred at a time.
"One embryo at a time is safest during IVF treatment."
Elizabeth Sullivan, MD, MPH, from the Perinatal and Reproductive Epidemiology Research Unit of the University of New South Wales in Sydney, Australia, and a colleague looked 50,258 births that occurred from IVF and ICSI pregnancies.
ICSI, or intracytoplasmic sperm injection, is the process of injecting sperm into an egg outside of the woman's body to create an embryo for transplantation.
All the births occurred at least 20 weeks along in pregnancy and with babies that were at least 400 grams (14 ounces).
Dr. Sullivan and her colleague, Y. Alex Wang, MPH, from the same institution, defined a "perinatal" death (one occurring before, during or after birth) as either a stillbirth or an infant who dies within the first 28 days of life.
During the study period, 813 perinatal deaths occurred, including 630 stillbirths and 183 newborn deaths, for an overall rate of 16.2 per 1,000 births.
When they compared the birth rate in women who had two embryos transferred to the rate in women with a single embryo transfer, they found that the two-embryo-transfer pregnancies resulted in a higher rate of deaths.
Women who received two embryos experienced an infant death rate of 19.1 deaths per 1,000 births, while those receiving only a single embryo transfer had 13.2 deaths per 1,000 births.
This difference translated into a 53 percent higher risk of a baby's death in a pregnancy involving two embryo transfers instead of one.
When comparing births from fresh embryos to those from frozen embryos, the mortality rate was even higher: the transfer of two fresh embryos was associated with a 74 percent higher likelihood of the baby dying than in pregnancies that occurred following a single fresh embryo transfer.
The higher rate of death was due, in part, to multiples in the pregnancies. About half of the babies who died in their first month of life were twins, which comprised one third of the total perinatal mortality rate for newborn death and stillbirth combined.
The rate for death among twins was 27.8 per 1,000 births compared to 12.4 per 1,000 for single children.
Interestingly, the type of twin made a difference in the rates as well - in the opposite direction as the other results. Identical twins who resulted from a single embryo transfer had a lower survival rate than fraternal twins who developed from two different embryos.
According to Dr. Sullivan, after Australia and New Zealand doctors voluntarily adopted a policy of implanting only single embryos in IVF, the countries saw a drop in overall mortality among IVF babies in their first month of life or after their 20th week in the womb.
Therefore, doctors 'Down Under' continue to recommend the transfer of only a single embryo in IVF cycles for women under age 35 because of the reduced rate of deaths and other benefits.
"The number of embryos transferred per procedure is the major determinant of multiple pregnancy and multiple delivery, which contribute to an elevated risk of preterm birth and low birth weight, and its [related problems]," Dr. Sullivan said. "These are risks in addition to those already faced by women being treated for infertility."
She reported a correlation between single embryo transfer rates and a reduced rate in multiples' births in Australia and New Zealand.
In 1999, only 14 percent of IVF transfers were of single embryos; in 2008, single embryo transfers accounted for 68 percent of all IVF transfers. Over nearly the same time, deliveries of multiples declined from 22.1 percent in 2000 to 8.4 percent in 2008.
The study was presented July 4 at the 28th annual meeting of the European Society of Human Reproduction and Embryology in Istanbul.
Because the study has not yet been published in a peer-reviewed journal, its results should be regarded as preliminary and still require review by researchers in the field. No information was available regarding funding or disclosures.