Asians are nine times as likely as other women to experience severe tearing of the skin around the vagina during childbirth, Israeli researchers report.

They also found that vacuum-assisted delivery, giving birth for the first time, and a front-facing orientation of the baby in the birth canal were linked to higher risks.

Still, severe tears of the perineum - the area between the vagina and the anus - were rare, affecting only a quarter of one percent of women studied.

Such perineal tears can sometimes have long-lasting effects, including incontinence and pain during sexual intercourse. As a consequence, said researcher Dr. Asnat Groutz of the Lis Maternity Hospital in Tel Aviv, closer monitoring during pregnancy or elective cesarean section may be warranted in some cases.

Writing in the American Journal of Obstetrics and Gynecology, the researchers report 96 severe tears among 38,252 vaginal, single-birth deliveries at their hospital.

Women of Asian ethnicity were more likely to have the problem, with 2.5 percent of them experiencing third- or fourth-degree tears.

Mild vaginal tearing occurs in nearly three-quarters of vaginal births. Sometimes a physician will make a cut - called an episiotomy - to avoid a tear and assist in the delivery, but this practice is controversial.

Severe ruptures that can stretch from the vagina to the anus are much less common, but despite the severity, some severe tears may go undetected and untreated.

“Up to 87% of severe tears are misdiagnosed by midwives, and up to 24% are misdiagnosed by doctors,” Groutz said.

Why Asian woman appear to be at increased risk of severe perineal tearing isn’t clear. A shorter perineum less able to stretch during delivery coupled with bigger babies following adoption of western eating habits is one possibility. But very little research exists on such injuries in these women’s home countries for comparison, the researchers point out.

“Further studies are needed to explore the mechanisms for this clinical observation,” Groutz said.

In the meantime, physicians can be more aware of the increased risk and change the care they give by keeping a closer eye on the baby’s size, providing more perineal support during delivery, and considering C-section delivery before labor begins, Groutz said.

SOURCE: American Journal of Obstetrics and Gynecology, online December 22, 2010.