SAN DIEGO – As birth weight increases, progression in labor was slower both in successful trial of labor patients and in patients who ultimately had cesarean deliveries.
The findings come from a retrospective review of electronic data from the Consortium on Safe Labor, an observational study of labor and delivery practices led by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) and the National Institutes of Health (NIH) that was conducted at 12 clinical centers from 2002 to 2008.
Doug Brunk/IMNG Medical Media
Dr. Heidi K. Leftwich
"Since the 1950s, obstetricians have been using the Friedman labor curve in order to assist in interpreting normal and abnormal labor patterns," lead study author Heidi K. Leftwich, D.O., said at the annual meeting of the American College of Obstetricians and Gynecologists.
"However, we have [a] very different patient population these days. There is more obesity, less active management of the second stage of labor, we use more epidurals, and we have an older population, with women waiting later to begin their families."
With the cesarean section rate escalating, she continued, "current research has been focusing on variables which might alter the labor curve, and challenging the notion that one labor curve can apply to all women."
The objective of the current study was to examine data from the Consortium on Safe Labor to determine whether birth weight alters the labor pattern in nulliparas and multiparas. Inclusion criteria consisted of patients with cephalic presentation, singleton gestation, gestational age of 34 weeks or more, who had undergone two or more cervical exams. Those patients with fetal anomalies, elective repeat cesarean section, and lacking birth weight data were excluded from the study.
The researchers created five birth weight categories separated by 500 g increments: less than 2,500 g (category 1), 2,500-2,999 g (category 2), 3,000-3,499 g (category 3), 3,500-3,999 g (category 4), and greater than or equal to 4,000 g (category 5). They used interval-censored regression to estimate the duration of labor, or "traverse times," and repeated measures analysis to construct mean labor curves by parity as well as by birth weight categories.
"The traverse times is more of an approximation of the time it takes for the cervix to dilate a centimeter," explained Dr. Leftwich, a fellow of maternal-fetal medicine in the department of obstetrics and gynecology at the University of Illinois at Chicago. "This is stratified by cervical dilation at admission, as well as exams performed in labor."
A total of 146,904 maternal records met inclusion criteria. Cesarean sections occurred in 21% of group 1, 14% of group 2, 14% of group 3, 17% of group 3, and 25% of group 5. Dr. Leftwich reported that in nulliparas, traverse times increased as birth weight increased, for both vaginal and cesarean deliveries (P less than .001). In multiparas, traverse times increased as birth weight increased from 5-8 cm dilation, for both vaginal and cesarean deliveries (P less than .001). "From 8 cm-10 cm, traverse times still increased by birth weight, but this was not statistically significant secondary to minimal cervical exams," Dr. Leftwich said.
A limitation of the study, she noted, was that "rapid progression of labor in multiparas makes traverse times less accurate for the active phase."
The study was supported by a contract from the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development and an award from the University of Illinois at Chicago Center for Clinical and Translational Science. Dr. Leftwich said that she had no relevant financial disclosures.