Characterizing labor progression and duration according to maternal body mass index

This study aimed to describe labor progression and duration according to the maternal body mass index in patients who underwent vaginal delivery.

This was a retrospective cohort study of all vaginal deliveries at a large, tertiary hospital in New York City from January 1, 2013, to December 31, 2022. Singleton births of cephalic-presenting fetuses delivered vaginally at ≥37 weeks of gestation were included, with at least 2 documented cervical examinations between 2- and 10-cm dilations. Body mass index was documented from delivery admission or within 30 days before delivery and classified according to the categories of the Institute of Medicine. All demographic information, clinical characteristics, cervical examinations, and obstetrical outcomes were abstracted from the electronic medical record. Outcomes included length of the latent phase, active phase, and total first stage of labor. Labor curves were constructed for each body mass index group and further subcategorized by parity and induction of labor vs spontaneous labor.

Among 41,868 patients who met inclusion criteria, 9491 (22.7%) had normal weight or were underweight, 19,658 (47.0%) were overweight, 8880 (21.2%) had class 1 obesity, 2826 (6.7%) had class 2 obesity, and 1013 (2.4%) had class 3 obesity. Labor duration differed by body mass index class, with a positive monotonic pattern observed between increasing body mass index class and time in latent labor and the first stage of labor. The duration of active labor did not differ between individuals who were overweight or obese and those with normal weight. The results were similar in subgroup analyses based on parity and presence of spontaneous labor vs labor induction.

Higher body mass index was associated with slower labor progress and longer labor duration in patients who underwent vaginal delivery. This difference was driven by longer times spent in latent labor, with no significant difference observed in active labor. The results suggest a potential need for the use of labor curves more specifically tailored to body mass index when assessing for progress in labor to avoid unnecessary cesarean deliveries.