Gaining weight during pregnancy causes increased risk for tears during delivery

Montefiore Medical CenterMay 8 2013

Excessive weight gain during pregnancy significantly increases the risk of lacerations during vaginal childbirth, according to a study conducted by researchers at Montefiore Medical Center. Among more than 1,000 women who participated in the study, 126 experienced a significant increase in their body mass index (BMI), both +1 and +2 category changes, according to the criteria established by the World Health Organization (WHO). Of those women, 85.5 percent experienced lacerations compared to 69 percent with no change in BMI category. The study was presented today in New Orleans at the annual meeting of the American College of Obstetricians and Gynecologists.

"Excessive weight gain during pregnancy can result in larger babies, so we wanted to study whether there is increased risk for tears to the mother's vagina during delivery," said Diana Garretto, M.D., Department of Obstetrics & Gynecology and Women's Health, Montefiore Medical Center, and Instructor, Department of Obstetrics & Gynecology and Women's Health, Albert Einstein College of Medicine of Yeshiva University. "Our results were noteworthy - when the mother gains too much weight, it causes increased risk for tears during delivery."

The most common injuries to the vagina during labor occur at the vaginal opening, which may tear as the baby's head passes through. For successful vaginal delivery, the cervix must dilate to at least 10 centimeters. When a woman gains too much weight, the larger baby may increase the risk for laceration.

About 30 percent of women who maintained a normal BMI were laceration-free. Among women who became overweight during pregnancy, however, only 20 percent had no lacerations, and for women who were obese, just 9 percent went through delivery without a tear.

Tears that occur in the posterior portion of the vagina can vary in severity. First degree lacerations, when the tear involves only the lining of the vagina, are the most common. A first degree tear doesn't usually bleed and may not require repair. A second degree laceration is when the tear extends into the submucosal tissues (the tissues just under the vaginal lining). Most second degree tears occur in the midline and extend towards the anus and require surgical repair.

More serious lacerations involve the deeper tissues, including the anal sphincter (third degree lacerations) or even the rectum and its lining (fourth degree lacerations). These lacerations are often difficult to repair and require surgery. Third and fourth degree tears are more likely to cause complications, including infection, bleeding, anal incontinence and increased pain.

A single institution retrospective chart review of 1,031 patients who delivered at term over seven months was performed. Patients were categorized into BMI classes at pre-pregnancy and term. Pre-pregnancy BMI categories are, according to WHO, normal weight -- 18-25, overweight -- 25-30, and obese -- 30 and above. Based on the 2009 IOM guidelines for appropriate weight gain during pregnancy, BMI was classified as underweight - less than 23.5, normal weight - 23.5-29.9, overweight - 30-33, and obese - greater than 33.5.