June 7, 2010 / 9:19 PM / in 9 years

More evidence preterm birth can run in families

NEW YORK (Reuters Health) - Women who were born prematurely or had siblings who were may be at increased risk of having a preterm baby themselves, a large UK study finds.

The findings, from a study of nearly 14,000 women who gave birth between the 1970s and 2008, add to evidence that genes are involved in the risk of preterm delivery (birth before the 37th week of pregnancy).

Researchers found that women who were either born prematurely or had siblings who were had a 35 percent to 49 percent greater chance of preterm delivery, compared with women without such a family history.

The risk to any one woman, however, was not great, according to findings published in the journal Obstetrics & Gynecology.

Among women born preterm, 9 percent had a premature baby themselves. That compared with just over 6 percent of women who had been born full-term.

So while the findings bolster evidence for a role of family history in preterm birth, they are not going to change how women’s pregnancies are managed, according to an editorial published with the study.

That is, women who were born preterm do not need to be considered high-risk for premature delivery and monitored with extra prenatal tests, writes Dr. William H. Barth, Jr., of Harvard Medical School and Massachusetts General Hospital in Boston.

Instead, he says, the findings are mainly of interest to researchers who are trying to uncover the reasons underlying preterm delivery.

In general, experts believe that preterm birth results from a complex mix of genetic susceptibility and environmental factors and behaviors. Some of those factors have been identified; studies suggest, for example, that smoking and drug use, as well as certain infections — particularly genital infections — raise the risk of preterm birth. But in most cases, the cause is unknown.

Recent studies have solidified the belief that genes play a role. In one that analyzed nearly 1 million births in Sweden, for instance, researchers found that sisters of women who had delivered preterm had an 80 percent higher risk of early delivery, versus women without that family history.

There was no evidence that the increased risk shared by sisters was explained by non-genetic factors that could influence the chances of preterm delivery, like smoking or lower education level.

For the current study, Sohinee Bhattacharya and colleagues of the University of Aberdeen used information from a database that has tracked births among Aberdeen-area women since the 1950s.

They focused on births to 13,845 women whose own mothers were also included in the database. Of those women, 471 had been born preterm.

In general, the researchers found, women who had been born preterm were 49 percent more likely than their full-term counterparts to have a premature infant. That was with factors such as age, weight, smoking habits and socioeconomics taken into account.

Similarly, there was an increased risk among women whose mothers had had any preterm birth; they were 35 percent more likely to deliver prematurely than women without a similar family history.

Researchers do not know precisely how genes may influence preterm-birth risk. Genes that regulate the conditions of the uterus during pregnancy, for instance, may be involved, but that remains to be shown.

More studies are needed to pinpoint which genes play a role in preterm delivery, according to both Bhattacharya’s team and Barth, the editorialist.

If researchers can identify the genes involved, that would give more clues to the underlying causes of preterm birth, and possibly lead to new ways to prevent some cases.

SOURCE: here ed_Predisposition_to_Spontaneous_Preterm.6.aspx

Obstetrics & Gynecology, June 2010.

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