OBJECTIVE: To evaluate the relationship between the lengths of the first and second stages of labor.
METHODS: In this observational study of women delivering at our hospital, the onset of the first stage of labor was defined as admission at 3-cm to 4-cm dilatation in the presence of uterine contractions with or without rupture of membranes. This study was limited to nulliparous women with a singleton, cephalic live birth at 37 0/7 weeks of gestation or more. Women presenting with more advanced cervical dilatation (greater than 4 cm), prior cesarean delivery, diabetes, hypertension, and placental accidents were excluded. Each woman was analyzed based on her specific lengths of first and second stages of labor, that is, paired observations for each woman.
RESULTS: Between January 1, 2001, and June 30, 2012, a total of 172,522 women were delivered and 12,523 (7.3%) met the inclusion criteria. The 95th percentile was 15.6 and 2.9 hours for the first and second stages, respectively. Women with first stages greater than the 95th percentile had a 16.3% rate of a second-stage length greater than the 95th percentile compared with 4.5% (P<.001) in women with first stages less than the 95th percentile. This relationship persisted when analyzed for variables influencing labor to include neonate birth weight, epidural analgesia, or maternal size.
CONCLUSION: Overall, the length of the second stage significantly increased concomitantly with increasing length of the first stage (P<.001).
LEVEL OF EVIDENCE: II