Premature labor - also known as preterm labor - is the onset of rhythmic uterine contractions that produce cervical changes after fetal viability but before fetal maturity. It usually occurs between the 20th and 37th week of gestation. About 5% to 10% of pregnancies end prematurely; about 75% to 85% of neonatal deaths, and many birth defects, result 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 about 10%; 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 more than 50% ; those weighing 2 lb 3 oz to 2 lb 11 oz (992 to 1 ,219 g) and of more than 28 weeks' gestation have a 70% to 90% survival rate.
It is frustrating that there are few known actual causes of preterm labor. The above-mentioned risk factors are only associated findings, not actual causes.
Signs and Symptoms
The patient reports the onset of rhythmic uterine contractions, possible rupture of membranes, passage of the cervical mucus plug, and a bloody discharge. Her history indicates that she's in the 20th to 37th week of pregnancy. Inspection during vaginal examination shows cervical effacement and dilation.
Premature labor is confirmed by the combined results of prenatal history, physical examination, and presenting signs and symptoms. Various diagnostic studies support the diagnosis.
Ultrasonography is used to identify the position of the fetus in relation to the mother's pelvis, document gestational age, and estimate fetal weight.
Vaginal examination is used to confirm progressive cervical effacement and dilation.
Electronic fetal monitoring confirms rhythmic uterine contractions and is used to monitor fetal wellbeing. Ambulatory home monitoring with a tocodynamometer may identify preterm contractions.
Differential diagnosis excludes Braxton Hicks contractions and urinary tract infection.
Medical management focuses on suppressing premature labor when tests show immature fetal pulmonary development, cervical dilation of less that 4 cm, and factors that warrant continuation of pregnancy.
Primary interventions include bed rest and hydration. If the patient doesn't respond, tocolytic therapy is instituted unless contraindicated. Beta-adrenergic stimulants (terbutaline, isoxsuprine, or ritodrine) stimulate the beta2 receptors, inhibiting the contractility of uterine smooth muscle.
Magnesium sulfate may be used to relax the myometrium. After successful tocolysis, oral therapy's maintained until 36 weeks' gestation. Some patients successfully deliver at term after this treatment. Glucocorticoid administration to the mother at less than 33 weeks' gestation enhances fetal pulmonary maturation and reduces the incidence of respiratory distress syndrome.
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. Regardless of where treatment and delivery take place, they require intensive team effort, focusing on:
ALERT Morphine or meperidine may be required to minimize maternal pain. These drugs have little effect on uterine contractions, but because they depress the central nervous system (CNS), they may cause fetal respiratory depression. They should be given the smallest dose possible and only when needed.
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 ries of this disorder.
A healthy lifestyle can go a long way toward preventing preterm labor and birth.
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