Study Shows Increase in Birth Defects Linked to Multiple Births

The number of birth defects among twins and triplets increased nearly two fold in 14 European countries between 1984 and 2007, according to a new study.

The new study suggests that birth defects are more likely to occur in multiple births, such as twins or triplets, than in single births. Researchers fear this growing problem may be linked to the increased use of fertility treatments.

“The importance of knowing this is two fold. First, to make sure we have appropriate services available for mothers and babies. The second is to understand the relationship,” said Professor Helen Dolk, the study’s senior author.

Dolk, from the Center for Maternal Fetal and Infant Research at the University of Ulster in Northern Ireland, said she and her fellow researchers knew multiple births were on the rise and that those babies were at an increased risk for birth defects.

For the new study, the researchers who published their findings in BJOG: An International Journal of Obstetrics and Gynecology, looked at the trends in births in 14 European countries between 1984 and 2007.

Of the 5.4 million births, the researchers found the number of multiple births increased by about 50 percent over that time. Ultimately, 3 percent of the births were multiple births.

Only 4 percent of the 143,359 major birth defects within those births occurred in babies who were multiples.

Over the 24-year period, though, the number of birth defects among multiples nearly doubled, with a peak between the years 2000 and 2003 of about 12 birth defects per 10,000 multiple births.

“The increase in multiple birth rates may be explained by changes in maternal age and increased use of assisted reproductive technology (ART). It is clear that more research needs to be done to determine the contribution of ART to the risk of congenital anomalies in multiple births.”

Prior research has found that from 1986 to 2002, there was a 35 percent increased risk of birth defects among babies born to mothers who underwent in vitro fertilization (IVF), a 72 percent increased risk with ICSI (intracytoplasmic sperm injection) and a 300 percent risk of Clomid birth defects.

The U.S. Food and Drug Administration (FDA) has received hundreds of post-marketing reports of birth defects after Clomid use since it was first approved in 1972. Some studies suggest the drug may as much as tripled the risk of birth defects when compared to women who conceived normally. However, a number of other studies have found either weaker or no associations at all.

It is not easy to definitively determine the cause of birth defects in children who were conceived through assisted means. For many years, researchers have been trying to determine whether side effects of Clomid increase the risk of birth defects, particularly neural tube defects (NTDs).

The largest increase was in birth defects not caused by chromosomal abnormalities, such as physical deformations, which increased from about 6 per 10,000 multiple births between 1984 and 1987 to about 11 per 10,000 births at the end of the study.

Compared to single births, the researchers found the risk of birth defects was about 27 percent higher for multiples.

According to the researchers, some of the increase in birth defects might be attributed to the increased use of IVF, which is known to come with an increased risk of anomalies.

The researchers write that people going through the IVF process might consider only implanting one embryo into a womb. While that may not cut down on the risk of a birth defect, it may affect the pregnancy outcome and put less of a strain on parents and resources.

“The fundamental message remains: the risks are low. Most babies are born healthy from multiple births or IVF, but there are a number of reasons why single embryo transfers is a better option than multiple embryo transfer,” Dolk said.

Transferring a number of embryos into a woman’s womb during iVF treatments is known to increase the risk of multiple births. Fertility clinics are now being advised to adopt a single embryo transfer (SET) policy.

In general, she added, people should talk with their doctors about reducing the risk of delivering a baby with a birth defect prior to becoming pregnant.

John Thorp, deputy editor-in-chief of BJOG, said, “Extra specialized help should be put in place for affected families, recognizing that there are now nearly double as many affected families than there were 20 years ago.”

“The discussion with the doctor should be before pregnancy and that doesn’t happen very often,” Dolk said.

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