Feb 8 (Reuters) - The number of birth defects among multiple births such as twins and triplets increased nearly two-fold in a score of European countries over a 24-year-period, according to an international study.

Researchers writing in BJOG: An International Journal of Obstetrics and Gynecology used data on more than 5.4 million births occurring between 1984 and 2007 to find that congenital defects rose from around 6 in every 10,000 multiple births to about 11 in every 10,000 multiples.

"The importance of knowing this is twofold," said senior author Helen Dolk, from the Centre for Maternal Fetal and Infant Research at the University of Ulster in Northern Ireland.

"First, to make sure we have appropriate services available for mothers and babies. The second is to understand the relationship," she added.

Dolk 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 study, they looked at the trends in births in 14 European nations between 1984 and 2007.

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

Of the 148,359 major birth defects within those births, about 4 percent occurred in babies who were multiples.

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

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 1985 to 1987 to about 11 per 10,000 multiples at the end of the study.

Compared to the births of singletons - or just one baby - the risk of birth defects was about 27 percent higher for multiples.

Some of the rise may be attributed to the increased use of in vitro fertilization (IVF), which is known to come with an increased risk of anomalies, the researchers said.

They wrote that people going through the IVF process might consider only transferring one embryo into the womb. While this might not cut down on the risk of birth defects, it could 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. SOURCE: http://bit.ly/VK3hEl

(Reporting from New York by Andrew Seaman at Reuters Health; editing by Elaine Lies)