**1. Introduction**

The second stage of labor is defined as the time from complete dilation of the cervix to delivery of the fetus. Several factors can influence the length of the second stage, including parity, maternal body mass index (BMI), fetal weight, fetal presentation, fetal position, and the use of analgesia [1]. In this chapter, we will focus on how obesity affects the duration of labor as the prevalence of obesity is rising among reproductive-aged individuals.

Obesity, defined as a BMI ≥ 30 kg/m2 , poses unique challenges for obstetrical providers throughout pregnancy. It increases the risk of hypertensive disorders, gestational diabetes, macrosomia, intrauterine growth restriction, and infections. Intrapartum care of obese women also presents challenges, including a higher rate of cesarean delivery and associated complications such as postoperative wound

infections, thromboembolic events, postpartum hemorrhage, endometritis, and delayed wound healing [1]. One study showed the rate of cesarean delivery during the second stage of labor in obese patients was twice as high as that in leaner individuals, especially for those with a BMI ≥ 35 kg/m2 [2]. Most of these cesarean deliveries were unscheduled due to labor arrest [2, 3].

Currently, the American College of Obstetricians and Gynecologists (ACOG) and Society for Maternal-Fetal Medicine (SMFM) define second stage of labor arrest as at least 2 hours of pushing in multiparous women and at least 3 hours of pushing in nulliparous women, with longer durations for epidural use and fetal malposition if progress is being documented [4]. However, the actual onset and duration of the second stage can be inaccurately recorded as the very definition of the beginning relies on an arbitrary time point when the examiner finds the cervix to be completely dilated. It would be reasonable to consider the cumulative length of time a patient is pushing, the number of pushes, and/or cumulative force generated as a clinical measurement to define the optimal length of the second stage and potentially change the trigger for diagnosis of second stage labor arrest. This would be a similar concept to using Montevideo units for defining adequate uterine contractility during the first stage of labor.

In this chapter, we will review the evidence on optimal management of the second stage of labor, with a focus on achieving vaginal delivery without increasing maternal and neonatal morbidities and mortalities.
