The association between fetal head station at the first diagnosis of the second stage of labor and delivery outcomes.

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Controversy surrounds the impact of the fetal head station on labor duration and mode of delivery. Whereas an extensive body of evidence has been published evaluating fetal head station in early labor, there is a paucity of data on the impact of fetal head descent during the second stage.To explore the association between fetal head station at the diagnosis of the second stage of labor and the second stage duration and the risk for operative delivery.A retrospective cohort study of all singleton vertex deliveries in a single tertiary center (2011-2016). Women were grouped according to fetal head station upon diagnosis of second stage: above (S<0), at the level (S=0) and below (S>0) the level of the ischial spine. The duration of the 2nd stage and the risk for operative delivery were compared between the groups and stratified by parity.Overall, 34,334 met the inclusion criteria. Of these, 18,743 (54.6%) were nulliparous and 15,591 (45.4%) were multiparous. Of the nulliparous women, 8.1%, 35.8% and 56.1% were diagnosed with fetal head above, at the level and below the ischial spine upon second stage diagnosis. Of the multiparous women, 19.7%, 35.6% and 44.7% were diagnosed with fetal head above, at the level and below the ischial spine. Fetal head station upon second stage diagnosis was independently and significantly associated with second stage duration, however, its contribution was 4.5-fold among nulliparous as compared to multiparous women. In multivariable analysis, after controlling for maternal age, gestational age at delivery, pre-pregnancy BMI, epidural anesthesia and birthweight, the risk for operative delivery was significantly increased in a dose-dependent pattern for both nulliparous and multiparous women.The fetal head station at the first diagnosis of the second stage is significantly and independently associated with the duration of the second stage and correlated with the risk for operative delivery in both nulliparous and multiparous women.

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