induction of labor

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Induction of Labor

 

Definition

Induction of labor involves using artificial means to assist the mother in delivering her baby.

Purpose

Labor is brought on, or induced, when the pregnancy has extended significantly beyond the expected delivery date and the mother shows no signs of going into labor. Generally, if the unborn baby is more than two weeks past due, labor will be induced. In most cases, a mother delivers her baby between 38-42 weeks of pregnancy. This usually means that labor is induced if the pregnancy has lasted more than 42 weeks. Labor is also induced if the mother is suffering from diseases (preeclampsia, chronic hypertension), if there is an Rh blood incompatibility between the baby and the mother, or if the mother or baby has a medical problem that requires delivery of the baby (like a premature rupture of the membranes).

Description

The uterus is the hollow female organ that supports the development and nourishment of the unborn baby during pregnancy. Sometimes labor is induced by the rupturing the amniotic membrane to release amniotic fluid. This is an attempt to mimic the normal process of "breaking water" that occurs early in the normal birth process. This method is sometimes enough stimulation to induce contractions in the mother's uterus. If labor fails to start, drugs are used.
Most labor is induced by using the drug Pitocin, a synthetic form of oxytocin. Oxytocin is a natural hormone produced in the body by the pituitary gland. During normal labor, oxytocin causes contractions. When labor does not occur naturally, the doctor may give the mother Pitocin to start the contractions. Pitocin makes the uterus contract with strength and force almost immediately. This drug is given through a vein in a steady flow that allows the doctor to control the amount the mother is given.
Sometimes vaginal gels are used to induce labor. Normally, the baby will pass through the opening of the uterus (the cervix) into the birth canal during delivery. Because of this, the cervix softens and begins to enlarge (dilate) during the early part of labor to make room for the baby to pass through. The cervix will continue to dilate, and the contractions will eventually push the baby out of the mother's body. When labor needs to be induced, the cervix is often small, hard, and not ready for the process. The doctor may need to prepare or "ripen" the cervix to induce labor. The hormone prostaglandin in a gel form may be applied high in the vagina to soften and dilate the cervix, making the area ready for labor. This may be enough to stimulate contractions on its own. More often, prostaglandin gel is used in conjunction with Pitocin.
If all attempts to induce labor fail, a cesarean section is performed.

Risks

Once labor has been induced, the unborn baby is monitored to guard against a reduction in its oxygen supply, or hypoxia. The drugs used to induce labor cause vasoconstriction, which can decrease blood supply to the unborn baby. Throughout the process, the baby's heart rate is monitored by an electronic device placed on top of the mother's abdomen. The heart rate is one sign that the unborn baby is getting enough oxygen and remains healthy. Once the membranes are broken, prolonged labor may result in infection to either the newborn or the mother.

Normal results

Once labor is induced and the cervix has dilated, labor usually proceeds normally. When performed properly, induced labor is a safe procedure for both mother and baby.

Resources

Books

Berkow, Robert, et al., editors. The Merck Manual of Medical Information. Whitehouse Station, NJ: Merck Research Laboratories, 2004.

Key terms

Cesarean section — Delivery of a baby through an incision in the mother's abdomen instead of through the vagina; also called a C-section.
Preeclampsia — Hypertension (high blood pressure) experienced during pregnancy.
Rh blood incompatibility — A blood type problem between mother (who is Rh negative) and baby (who is Rh positive), making the immune system of the mother attack her unborn baby. During delivery of the first pregnancy, the mother's immune system becomes sensitive to the Rh positive blood of the baby. The mother's system may then attack later pregnancies and cause severe illness or death to those babies.
Vasoconstriction — Constriction of a blood vessel.

induction of labor

an obstetric procedure in which labor is initiated artificially by means of amniotomy or administration of oxytocics. It is performed electively or for fetal or maternal indications. Elective induction is carried out for the convenience of the mother or the obstetrician, often to avert the possibility of delivery outside the hospital when labor is judged to be imminent and the mother is expected to have an unusually rapid birth. Elective inductions are performed less often now than in the past. Prerequisites for elective induction are a term gestation, a fetal weight of at least 2500 g, a cervix judged ready to dilate, a vertex presentation, and engagement of the presenting part of the fetus in the pelvis. Errors in the estimation of gestational age and fetal weight may result in the delivery of an unexpectedly immature or low-birth-weight infant. Indicated induction is performed when its risk is judged to be less than that of continuing the pregnancy in such conditions as premature rupture of the membranes, severe maternal diabetes, and intractable preeclampsia. Surgical induction is effected by amniotomy, often with stripping of the membranes and digital stretching of the cervix; it is very often carried out in conjunction with medical induction. Medical induction is achieved through the administration of oxytocin, almost always by IV infusion, in a carefully controlled manner using microdrip equipment or an infusion pump. Beginning with very small amounts of oxytocin in an IV solution, the dosage is increased by gradual increments of the rate or concentration of infusion until effective labor is established. With IV oxytocin inductions a secondary, piggyback infusion without medication is always attached to the tubing so that an unmedicated infusion can be maintained if oxytocin is stopped. Prostaglandins are more commonly used to induce labor in the second trimester, particularly for therapeutic abortions. Electronic fetal and uterine monitoring is usually instituted during induction of labor to prevent hyperstimulation of the uterus and fetal distress. Ideally induced labor mimics natural labor, but in practice it usually does not. Longer and harder contractions commonly occur. In addition to unexpected fetal immaturity, complications of induction of labor include umbilical cord prolapse after amniotomy, tumultuous labor, tetanic uterine contractions, rupture of the uterus, placental abruption, fetal maternal hypotension, water intoxication, postpartum uterine atony and hemorrhage, and fetal asphyxia, hypoxia, or death. If the induction fails to produce effective labor, cesarean section is often required to prevent the adverse sequelae of the procedures used in the induction. For this reason it is usually recommended that induction of labor not be attempted unless delivery must be accomplished to prevent severe fetal or maternal morbidity.

induction of labor

The use of artifical maneuvers to hasten the onset of labor, including the use of prostaglandin E2 gel, oxytocin infusion, and amniotomy; in post-term pregnancy, induction of labor results in a lower rate of cesarean section than serial antenatal monitoring

in·duc·tion of la·bor

(in-duk'shŭn lā'bŏr)
Medical attempt to improve the process of giving birth through drugs or surgical interventions and manipulation.