The researchers investigated the association between adverse pregnancy outcome, assisted reproduction technology (ART), and a previous diagnosis of endometriosis in 1 442 675 single births to Swedish women. They found 13 090 births among 8922 women diagnosed with endometriosis. Compared with women without endometriosis, they had a 1.33 greater risk of preterm birth. Women with endometriosis were also more likely to have difficulty in conceiving and need to receive ART, which is itself a risk factor for adverse pregnancy outcome.

Among women with endometriosis, 11.9% conceived after ART compared with the 1.4% of women without endometriosis who used the technique. The risk of preterm birth associated with endometriosis among women with ART was 1.24, and among women without ART 1.37.

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

Endometriosis is a chronic inflammatory disease, affecting up to 15% of all women of reproductive age, in which the endometrial cells that line the uterus are deposited in other areas.

Such displacement of endometrial cells can lead to anatomical distortion and also the release of anti-inflammatory cytokines, signalling molecules used in communication between cells. Symptoms of endometriosis include severe pelvic pain, heavy menstrual periods, and nausea.

In addition to an increased risk of preterm birth, the researchers also found other differences in the pregnancies of women with endometriosis. "Nearly twice as many women in this group were delivered by Caesarean section," said Dr. Falconer. "We observed that among these women the risk of induced preterm birth was higher than for spontaneous preterm birth. We believe that women with endometriosis are more frequently scheduled for preterm Caesarean section, possibly due to placental complications."

Women with endometriosis were also more likely to suffer from pre-eclampsia, a 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. Antepartal bleeding was also found to be more common among women with endometriosis, the researchers say.

"Because endometriosis is so strongly associated with infertility," said Dr. Falconer, "we were not surprised to find that women suffering from it were of higher maternal age and had fewer children. However, after adjusting for maternal age and other confounding factors, the strong association between endometriosis and risky pregnancies still remained.

"Our research provides clinicians with important information in the search for the factors associated with premature birth. 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."

This research was published in Human Reproduction. doi:10.1093/humrep/dep186

Note: If no author is given, the source is cited instead.

• Gynecology
• Pregnancy and Childbirth
• Menopause
• Infant's Health
• Women's Health
• Teen Health

• Gynecologic hemorrhage
• Hysterectomy
• Infertility
• Gynaecology
• Premature birth
• Nutrition and pregnancy