February 5, 2010 — As neonatal weight increases, so do the risks of adverse obstetric outcomes — including uterine rupture — in women giving birth vaginally after a prior cesarean delivery, new research suggests.
In light of this finding, the authors conclude that “estimated fetal weight should be included in the decision-making process for all women contemplating a trial of labor after cesarean delivery.”
Prior research has linked fetal macrosomia with various adverse obstetric outcomes, including emergency cesarean delivery, perineal laceration, first and second stages of labor dystocia, and shoulder dystocia, according to the report in the February issue of Obstetrics & Gynecology. Few trials, however, have examined these outcomes in women undergoing vaginal birth after cesarean delivery.
To investigate, Dr. Emmanuel Bujold, from Universite Laval, Quebec, Canada, and colleagues reviewed the medical records of all women who underwent a trial of labor following a prior low transverse cesarean delivery at Sainte-Justine Hospital from 1987 to 2004.
The women were divided into categories based on their infants’ birth weights. The reference group, designated group 1, had infants weighing less than 3500 g. Groups 2 and 3 had infants weighing 3500 to 3999 and 4000 g or more, respectively.
Of the 2586 women who were seen during the study period, 1519 (59%) were in group 1, 798 (31%) in group 2, and 269 (10%) in group 3, the researchers report.
Birth weight was directly linked to the rate of failed trial of labor. For group 1, the rate was 19%, whereas for groups 2 and 3, the rates climbed to 28% and 38%, respectively (p < 0.01).
Likewise, the authors found direct correlations between birth weight and the rates of uterine rupture (0.9%, 1.8%, and 2.6% for groups 1, 2, and 3, p < 0.05), shoulder dystocia (0.3%, 1.6%, and 7.8%, p < 0.01), and third- and fourth-degree perineal laceration (5%, 7%, and 12%, p < 0.01).
After accounting for potential confounders, a birth weight of 4000 g or more was associated with more than twofold increased risks of uterine rupture (OR, 2.62), failed trial of labor (OR, 2.47), and third- and fourth-degree perineal laceration (OR, 2.64). For shoulder dystocia, a particularly elevated risk was seen: OR, 25.13.
“Current recommendations of the American College of Obstetricians and Gynecologists and the Society of Obstetricians and Gynecologists of Canada state that fetal macrosomia should not be a contraindication for a trial of labor although it is associated with a lower likelihood of successful vaginal birth after cesarean delivery,” Dr. Bujold’s team notes.
“Based on our data,” they continue, “we believe that women with a previous cesarean delivery and an estimated fetal weight of 4000 g or more should be informed about their higher risks of uterine rupture and other adverse outcomes. Such women with no previous vaginal delivery should be told about the high risk…of uterine rupture.”
Obstet Gynecol. 2010;115:338-343. Abstract
Reuters Health Information 2010. © 2010 Reuters Ltd.
