A Little Chill Can Be Better for Babies

Frozen embryo IVF babies tend to fare a little better than fresh embryo IVF babies

/ Author:  / Reviewed by: Robert Carlson, M.D

(RxWiki News) Couples unable to conceive a child naturally may turn to fertility options. Within fertility treatments, however, couples have a variety of choices to make. Do any make a difference?

For those who use in vitro fertilization (IVF), one choice might make a small difference. IVF involves fertilizing the egg with the sperm outside of the woman's body and then inserting the fertilized egg into the woman in hopes she will become pregnant.

Couples who choose IVF can choose to use freshly fertilized embryos. Or they can fertilize the eggs, freeze the embryos and then implant them later.  

A recent unpublished study found that women receiving frozen embryos tended to have a slightly lower rate of poor pregnancy outcomes than women using fresh embryos.

Women carrying babies not conceived from IVF tended to have slightly better outcomes than women who became pregnant with IVF. The study was presented at a medical conference about pregnancy. None of the outcome differences related to miscarriage or stillbirth.

"Ask your doctor about fertility options."

The study, led by Ulla-Britt Wennerholm, MID, of the Obstetrics and Gynecology department at Sahlgrenska University Hospital in Göteborg, Sweden, aimed to compare the outcomes of IVF pregnancies using frozen embryos to those using fresh embryos.

They also compared the pregnancy outcomes of these two types of IVF births to the outcomes of non-IVF pregnancies.

The researchers analyzed all IVF treatments that occurred in Denmark, Norway and Sweden from 1984 to 2007. Then they compared these to the birth records during that time in those countries.

There were a total of 6,653 babies born following IVF using a frozen embryo transfer. A total of 42,287 babies were born following IVF using a fresh embryo.

A total of 288,868 other babies were born to parents who did not use IVF to conceive.

The researchers compared the rates of the following types of pregnancy outcomes:

  • low birth weight
  • very low birth weight
  • preterm birth
  • very preterm birth
  • underweight (small for gestational age)
  • overweight (large for gestational age)
  • extremely overweight (macrosomia)
  • stillbirth

In general, the babies whose parents did not use IVF had the best overall outcomes, compared to the IVF babies. However, within the IVF babies, those who were conceived from a frozen embryo transfer tended to do a little better than those transferred from a fresh embryo.

The babies born by frozen embryo IVF were 10 percent less likely to be born early (before 37th week of pregnancy) than babies born by fresh embryo. They were also about 20 percent less likely to be born underweight or small for the number of weeks of pregnancy when they were born, as compared with fresh-embryo IVF babies.

However, babies born by frozen embryo IVF were about 40 percent more likely to be born large for their gestational age and 50 percent more likely to be born very overweight, a condition called macrosomia.

Compared to babies not born with IVF, babies born from frozen-embryo IVF procedures were about 40 percent more likely to be born early and 80 percent more likely to be born very early (before the 32nd week of pregnancy).

However, those numbers did not mean an IVF baby was more likely to be born very early than to be born early. These numbers were comparisons. Fewer babies in both groups were born very early. But a higher percentage of babies were born very early in the frozen-embryo IVF group than in the non-IVF group.

Babies born by frozen-embryo IVF were also more likely (30 percent) to have a low birth weight or very low birth weight (70 percent). They were 30 percent more likely to be large for gestational age and 40 percent more likely to be extremely overweight (macrosomia).

None of these increases or decreases in risk were extraordinarily large, and no differences in risk were found for stillbirths.

The researchers calculated that the differences were not due to coincidence or chance alone, but the risk differences should not be taken to mean that IVF is unsafe for a child or that the difference between using a fresh or frozen embryo will put a baby at significant risk.

The study also has not yet been published in a peer-reviewed journal, so these results should be regarded as preliminary and they still require review by researchers in the field.

The study was presented February 14 at the Society for Maternal-Fetal Medicine's annual meeting, The Pregnancy Meeting, in San Francisco. Information was unavailable regarding funding and conflicts of interest.

Reviewed by: 
Review Date: 
February 12, 2013
Last Updated:
February 16, 2013