NEW YORK (Reuters Health) – Pregnant women with endometriosis are at increased risk for delivering prematurely as well as suffering a number of other adverse pregnancy outcomes, results of a study indicate.

Endometriosis is a painful condition that affects women during their reproductive years and is caused by the growth of the tissue lining the uterus in other parts of the abdomen outside of the uterus, such as the ovaries. Symptoms of endometriosis include severe pelvic pain, heavy menstrual periods, and nausea.

"given that endometriosis is relatively common in women of childbearing age, we hope that our results will lead to pregnant women with this condition receiving extra attention, thus enabling them to have normal pregnancies and give birth to healthy babies," study co-author Dr. Henrik Falconer, of the Department of Woman and Child Health, Karolinska Institute, Stockholm, Sweden, noted in a statement.

Falconer and colleagues analyzed data on more than 1.4 million Swedish women who gave birth between 1992 and 2006 in Sweden. they identified 13,090 births among 8,922 women who had doctor-diagnosed endometriosis.

While 5 in 100 women without endometriosis delivered preterm (before 37 weeks of pregnancy instead of the normal 40 weeks), nearly 7 in 100 women with endometriosis delivered preterm. That translated to a 33% greater risk of preterm birth for women with endometriosis, the researchers found.

The risk of preterm birth remained relatively unchanged when the women were stratified by those who did and did not use assisted reproduction technology, or ART, such as in vitro fertilization, to become pregnant. ART itself can raise a woman’s risk of preterm delivery.

"Endometriosis appears to be a risk factor for preterm birth, irrespective of ART," Falconer said. "Our findings indicate that women with endometriosis may be considered a high risk group and have special care during pregnancy."

Women with endometriosis were also more likely to have difficulty becoming pregnant and to turn to ART to conceive. the researchers also found that delivery by C-section was almost twice as common in women with endometriosis compared to women without endometriosis.

Women with endometriosis were also more likely to suffer from pre-eclampsia, a potentially dangerous condition that develops in the second or third trimester of pregnancy and involves the development of high blood pressure and the presence of protein in the urine.

"the strong association between endometriosis and risky pregnancies still remained" after adjusting for numerous factors that might influence the results, Falconer said.

Falconer presented the findings at the European Society of Human Reproduction and Embryology conference held this month in Amsterdam, the Netherlands. the study is published in the latest issue of the journal Human Reproduction.

SOURCE: Human Reproduction, July 2009.

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