Premature labor
Premature labor: Excerpt from Professional Guide to Diseases (Eighth Edition)
Premature labor, also called preterm labor, is the onset of rhythmic uterine contractions that produce cervical change after fetal viability but before fetal maturity. It usually occurs between the 20th and 37th weeks of gestation. Approximately 5% to 10% of pregnancies end prematurely; about 75% of neonatal deaths and a great many birth defects stem from this disorder. Fetal prognosis depends on birth weight and length of gestation: Neonates weighing less than 1 lb 10 oz (737 g) and of less than 26 weeks’gestation have a survival rate of 40% to 50%; neonates weighing 1 lb 10 oz to 2 lb 3 oz (737 to 992 g) and of 27 to 28 weeks’gestation have a survival rate of 70% to 80%; those weighing 2 lb 3 oz to 2 lb 11 oz (992 to 1,219 g) and of 28 weeks’ gestation have an 85% to 97% survival rate.
Causes and incidence
The possible causes of premature labor are many; they may include premature rupture of the membranes (occurs in 30% to 50% of premature labors), preeclampsia, chronic hypertensive vascular disease, hydramnios, multiple pregnancy, placenta previa, abruptio placentae, incompetent cervix, abdominal surgery, trauma, structural anomalies of the uterus, infections (such as rubella or toxoplasmosis), congenital adrenal hyperplasia, and fetal death.
Other important provocative factors include:
❑ Fetal stimulation: Genetically imprinted information tells the fetus that nutrition is inadequate and that a change in environment is required for well-being; this provokes onset of labor.
❑ Oxytocin sensitivity: Labor begins because the myometrium becomes hypersensitive to oxytocin, the hormone that normally induces uterine contractions.
❑ Myometrial oxygen deficiency: The fetus becomes increasingly proficient in obtaining oxygen, depriving the myometrium of the oxygen and energy it needs to function normally, thus making the myometrium irritable.
❑ Maternal genetics: A genetic defect in the mother shortens gestation and precipitates premature labor.
Signs and symptoms
Like labor at term, premature labor produces rhythmic uterine contractions, cervical dilation and effacement, possible rupture of the membranes, expulsion of the cervical mucus plug, and a bloody discharge.
Diagnosis
Premature labor is confirmed by the combined results of prenatal history, physical examination, presenting signs and symptoms, and ultrasonography (if available) showing the fetus’position in relation to the mother’s pelvis. Vaginal examination confirms progressive cervical effacement and dilation.
Treatment
Treatment is intended to suppress premature labor when tests show immature fetal pulmonary development, cervical dilation is less than 1½"(4 cm), and the absence of factors that contraindicate continuation of pregnancy. Such treatment consists of bed rest and, when necessary, drug therapy, but neither has been proven beneficial in all patients.
The following pharmacologic agents can suppress premature labor for up to 48 hours:
❑ Beta-adrenergic stimulants (terbutaline, isoxsuprine, or ritodrine): Stimulation of the beta2-adrenergic receptors inhibits contractility of uterine smooth muscle. Adverse effects include maternal tachycardia and hypotension, and fetal tachycardia.
❑ Magnesium sulfate: Direct action on the myometrium relaxes the muscle. It also produces maternal adverse effects, such as drowsiness, slurred speech, flushing, decreased reflexes, decreased GI motility, and decreased respirations. Fetal and neonatal adverse effects may include central nervous system (CNS) depression, decreased respirations, and decreased sucking reflex.
Maternal factors that jeopardize the fetus, making premature delivery the lesser risk, include intrauterine infection, abruptio placentae, placental insufficiency, and severe preeclampsia. Among the fetal problems that become more perilous as pregnancy nears term are severe isoimmunization and congenital anomalies.
Ideally, treatment for active premature labor should take place in a regional perinatal intensive care center, where the staff is specially trained to handle this situation. In such settings, the neonate can remain close to his parents. (Community health care facilities commonly lack the equipment necessary for special neonatal care and transfer the neonate alone to a perinatal center.)
Treatment and delivery require an intensive team effort, focusing on:
❑ continuous assessment of the neonate’s health through fetal monitoring
❑ administration of antenatal steroids to assist fetal lung development, unless contraindicated
❑ maintenance of adequate hydration through I.V. fluids.
Prevention of premature labor requires good prenatal care, adequate nutrition, and proper rest. Insertion of a purse-string suture (cerclage) to reinforce an incompetent cervix at 14 to 18 weeks’gestation may prevent premature labor in patients with histories of this disorder. However, this can be dangerous if an incompetent cervix is misdiagnosed and premature labor is the true cause.
Special considerations
A patient in premature labor requires close observation for signs of fetal or maternal distress, and comprehensive supportive care.
❑ During attempts to suppress premature labor, maintain bed rest and administer medications, as ordered. Give sedatives and analgesics sparingly, because they can have potentially harmful effects on the fetus. Minimize the need for these drugs by providing comfort measures, such as frequent repositioning and good perineal and back care.
❑ When administering beta-adrenergic stimulants, sedatives, and opioids, monitor blood pressure, pulse rate, respirations, fetal heart rate, and uterine contraction pattern. Minimize adverse effects by keeping the patient in a lateral recumbent position as much as possible. Provide adequate hydration.
❑ Tocolytic therapy has never been shown to benefit fetal morbidity and mortality; it’s best used to delay delivery for 48 hours while allowing antenatal steroids to effect lung development in the fetus.
❑ When administering magnesium sulfate, monitor neurologic reflexes. Watch the neonate for signs of magnesium toxicity, including neuromuscular and respiratory depression.
❑ Offer emotional support to the patient and her family. Encourage the parents to express their fears concerning the neonate’s survival and health.
❑ During active premature labor, remember that the premature neonate has a lower tolerance for the stress of labor and is much more likely to become hypoxic than the term neonate. If necessary, administer oxygen to the patient through a nasal cannula. Encourage the patient to lie on her left side or sit up during labor; this position prevents caval compression, which can cause supine hypotension and subsequent fetal hypoxia. Observe fetal response to labor through continuous fetal monitoring. Prevent maternal hyperventilation; a rebreathing bag may be necessary. Continually reassure the patient throughout labor to help ease her anxiety.
❑ Help the patient get through labor with as little analgesic medication and anesthetic as possible. To minimize fetal CNS depression, avoid administering analgesics when delivery seems imminent. Monitor fetal and maternal response to local and regional anesthetics.
❑ Explain all procedures. Throughout labor, keep the patient informed of her progress and the fetus’condition. If the father is present during labor, allow the parents some time together to share their feelings.
❑ A prepared resuscitation team, consisting of a physician, nurse, respiratory therapist, and an anesthesiologist or anesthetist, should be in attendance to take care of the neonate immediately. Have resuscitative equipment available in case of neonatal respiratory distress.
❑ Inform the parents of their child’s condition. Describe his appearance and explain the purpose of any supportive equipment. Help them gain confidence in their ability to care for their child. Provide privacy and encourage them to hold and feed the neonate, when possible.
❑ As necessary, before the parents leave the facility with the neonate, refer them to a community health nurse who can help them adjust to caring for a premature neonate.
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
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