Pharmacy Clinic
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Labor "Childbirth"
Definition of labor
"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 (American College of Obstetricians and
Gynecologists [ACOG], 2003; Norwitz, 2003).
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 incompetence, whereas uterine
contraction without cervical change does not meet the definition of labor."
emedicine.com
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 approximately 10 cm. In his landmark studies of 500 nulliparas, Friedman
(1955) subdivided the first stage into an early latent phase and an ensuing active phase.
The latent phase describes the period between the onset of labor and when the rate of
cervical dilatation changes most rapidly, usually at about 3-4 cm of cervical dilatation. The
active phase heralds a period of increased rapidity of cervical dilation and ends with
complete cervical dilation of 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 curve,
and a series of definitions of labor protraction and arrest were subsequently established
(Friedman, 1961 and 1961). However, subsequent data suggest that the rate of cervical
dilatation is slower and the progression of labor may be significantly different from that
shown on the Friedman curve (Kilpatrick, 1989; Albers, 1996; Zhang, 2002).
Second stage of labor "Full pdf chapter"
The second stage begins with complete cervical dilatation and ends with the delivery of
the fetus. The ACOG has suggested that a prolonged second stage of labor should be
considered when the second stage exceeds 3 hours if regional anesthesia is administered
or 2 hours in the absence of regional anesthesia in 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 (ACOG, 2003).
Studies performed to examine perinatal outcomes associated with a prolonged second
stage of labor revealed increased risks of surgical deliveries and maternal morbidities but
no differences in neonatal outcomes (Menticoglou 1995; Janni, 2002; Cheng, 2003;
Myles, 2003). Maternal risk factors associated with a prolonged second stage include
nulliparity, maternal weight and/or weight gain, use of regional anesthesia, induction of
labor, fetal occiput in a posterior position, and increased birthweight (Cheng, 2003; Myles
2003; O'Connell, 2003; Senécal, 2005).
Third stage of labor "Full pdf chapter"
The third stage of labor lasts from the delivery of the fetus until the delivery of the
placenta and fetal membranes. Although delivery of the placenta requires less than 10
minutes, the duration of the third stage of labor may last as long as 30 minutes before
active intervention is commonly considered (Norwitz, 2003).
Drugs during Labor
In an uncomplicated pregnancy, drug use during labor and delivery involves primarily
oxytocin and narcotic analgesics. Oxytocin is a uterotonic agent, and it induces or
augments labor. Pain is a frequent occurrence that requires drug therapy at or near term.
Less frequently encountered pregnancy conditions and complications requiring drug
treatment include infections or infection prophylaxis, fetal lung immaturity, preeclampsia
and eclampsia, cervical ripening and labor induction, preterm labor and delivery, and
postpartum hemorrhage (PPH). Medications routinely used in a labor-delivery unit are a
small fraction of those used in some other patient care areas of a hospital, such as the
intensive care or general medical units. However, a unique characteristic of drug therapy
during labor is that treatment is intended for one patient (mother or fetus) but a second
patient is always exposed (mother or fetus). Maternal status is usually the primary focus
of drug administration, but it must also focus on the fetus and the risk of developmental
toxicity. From American Journal of Health-System Pharmacy
Drugs are also used during labor to control pain
