Labor is a physiologic process during which the products of conception (ie, the fetus, membranes, umbilical cord, and placenta) are expelled outside of the uterus. Labor is achieved with changes in the biochemical connective tissue and with gradual effacement and dilatation of the uterine cervix as a result of rhythmic uterine contractions of sufficient frequency, intensity, and duration.1,2 Labor is a clinical diagnosis. The onset of labor is defined as regular, painful uterine contractions resulting in progressive cervical effacement and dilatation. Cervical dilatation in the absence of uterine contraction suggests cervical insufficiency, whereas uterine contraction without cervical change does not meet the definition of labor. Stages of Labor and Epidemiology
Stages of Labor
Obstetricians have divided labor into 3 stages that delineate milestones in a continuous process. First stage of labor
The first stage begins with regular uterine contractions and ends with complete cervical dilatation at 10 cm. In Friedman's landmark studies of 500 nulliparas3 , he subdivided the first stage into an early latent phase and an ensuing active phase. The latent phase begins with mild, irregular uterine contractions that soften and shorten the cervix. The contractions become progressively more rhythmic and stronger. This is followed by the active phase of labor, which usually begins at about 3-4 cm of cervical dilation and is characterized by rapid cervical dilation and descent of the presenting fetal part. The first stage of labor ends with complete cervical dilation at 10 cm. According to Friedman, the active phase is further divided into an acceleration phase, a phase of maximum slope, and a deceleration phase. Characteristics of the average cervical dilatation curve is known as the Friedman labor curve, and a series of definitions of labor protraction and arrest were subsequently established.4,5 However, subsequent data of modern obstetric population suggest that the rate of cervical dilatation is slower and the progression of labor may be significantly different from that suggested by the Friedman labor curve.6,7,8 Second stage of labor
The second stage begins with complete cervical dilatation and ends with the delivery of the fetus. The AmericanCollege of Obstetricians and Gynecologists (ACOG) has suggested that a prolonged second stage of labor should be considered when the second stage of labor exceeds 3 hours if regional anesthesia is administered or 2 hours in the absence of regional anesthesia for nulliparas. In multiparous women, such a diagnosis can be made if the second stage of labor exceeds 2 hours with regional anesthesia or 1 hour without it.1 Studies performed to examine perinatal outcomes associated with a prolonged second stage of labor revealed increased risks of operative deliveries and maternal morbidities but no differences in neonatal outcomes.9,10,11,12 Maternal risk factors associated with a prolonged second stage include nulliparity, increasing maternal weight and/or weight gain, use of regional anesthesia, induction of labor, fetal occiput in a posterior or transverse position, and increased birthweight.11,12,13,14 Third stage of labor
The third stage of labor is defined by the time period between the delivery of the fetus and the delivery of the placenta and fetal membranes. During this period, uterine contraction decreases basal blood flow, which results in thickening and reduction in the surface area of the myometrium underlying the placenta with subsequent detachment of the placenta.15 Although delivery of the placenta often requires less than 10 minutes, the duration of the third stage of labor may last as long as 30 minutes.
Expectant management of the third stage of labor involves spontaneous delivery of the placenta. Active management often involves prophylactic administration of oxytocin or other uterotonics (prostaglandins or ergot alkaloids), early cord clamping/cutting, and...