Preterm labor

What is preterm labor?

Preterm labor is labor that begins before 37 completed weeks of pregnancy. Although the exact definitions may vary, preterm labor may include one, or more, of the following:

  • uterine contractions.
  • rupture of the amniotic sac (membranes).
  • cervical dilatation (opening of the cervix).

The incidence of preterm labor and birth is about 5 to 10 percent overall.

What causes preterm labor?

Many factors can contribute to preterm labor. Although the exact cause of preterm labor is unknown in many cases, one major cause is premature rupture of membranes (breaking of the amniotic sac). Other related factors include the following:

Maternal factors:

  • preeclampsia (also known as toxemia or high blood pressure of pregnancy).
  • chronic medical illness (such as heart or kidney disease).
  • infection (such as group B streptococcus, urinary tract infections, vaginal infections, infections of the fetal/placental tissues).
  • drug abuse (such as cocaine, alcohol, tobacco and other drugs).
  • abnormal structure of the uterus.
  • cervical incompetence (inability of the cervix to stay closed during pregnancy).
  • previous preterm birth.

Factors involving the pregnancy:

  • abnormal or decreased function of the placenta.
  • placenta previa (low lying position of the placenta).
  • placental abruption (early detachment from the uterus).
  • premature rupture of membranes (amniotic sac).
  • hydramnios (too much amniotic fluid).

Factors involving the fetus:

  • when fetal behavior indicates the intrauterine environment is not healthy.
  • multiple gestation (twins, triplets, or more).
  • erythroblastosis fetalis (Rh/blood group incompatibility).

Why is preterm labor a concern?

Preterm birth is the greatest problem associated with preterm labor. Although most babies are born after 37 weeks, those born preterm are at increased risks for many complications.

Weeks of Pregnancy  less than 28 weeks 28-31   32-35 36 37-39 40 41
Percentage of Births 0.7  1.2 5.3 4.1 47 21 11

Premature babies are born before their bodies and organ systems have completely matured. These babies are often small, with low birthweight (less than 2,500 grams or 5.5 pounds), and they may need help breathing, eating, fighting infection, and staying warm. Very premature babies, those born before 28 weeks, are especially vulnerable. Many of their organs may not be ready for life outside the mother's uterus and may be too immature to function well.

Some of the problems premature babies may experience include:

  • temperature instability - inability to stay warm due to low body fat.
  • respiratory problems:
    • hyaline membrane disease/respiratory distress syndrome - a condition in which the air sacs cannot stay open due to lack of surfactant in the lungs.
    • chronic lung disease - long-term respiratory problems caused by injury to the lung tissue.
    • air leaking out of the normal lung spaces into other tissues.
    • incomplete lung development.
    • apnea or stopped breathing (occurs in about half of babies born at or before 30 weeks).
  • cardiovascular:
    • patent ductus arteriosus (PDA) - a heart condition that causes blood to divert away from the lungs.
    • too low or too high blood pressure.
    • low heart rate (often occurs with apnea).
  • blood and metabolic:
    • anemia (may require blood transfusion).
    • jaundice (due to immaturity of liver and gastrointestinal function).
    • too low or too high levels of minerals and other substances in the blood such as calcium and glucose (sugar).
    • immature kidney function.
  • gastrointestinal:
    • difficulty feeding (many are unable to coordinate suck and swallow before 35 weeks gestation).
    • poor digestion.
    • necrotizing enterocolitis (NEC) - a serious disease of the intestine common in premature babies.
  • neurologic:
    • intraventricular hemorrhage - bleeding in the brain.
    • periventricular leukomalacia - softening of tissues of the brain around the ventricles (the spaces in the brain containing cerebrospinal fluid).
    • poor muscle tone.
    • seizures (may be due to bleeding in the brain).
    • retinopathy of prematurity - abnormal growth of the blood vessels in a baby's eye.
  • infections (premature infants are more susceptible to infection and may require antibiotics).

Premature babies can have long-term health problems as well. Generally, the more premature the baby, the more serious and long lasting are the health problems.

Other problems associated with preterm labor include complications of the treatment. Medications used to treat preterm labor may have risks for the mother and fetus.

What are the symptoms of preterm labor?

The following are the most common symptoms of preterm labor. However, each woman may experience symptoms differently. Symptoms may include:

  • uterine contractions, especially more than four in one hour.
  • menstrual-type cramps.
  • pelvic pressure.
  • backache.
  • intestinal upset.
  • vaginal discharge of blood, mucus or water.

If you notice any symptoms of preterm labor, be sure to call your physician as soon as possible.

The symptoms of preterm labor may resemble other medical conditions. Always consult your physician for a diagnosis.

How is preterm labor diagnosed?

If preterm labor is suspected, most women are evaluated in the labor and delivery area of the hospital. Usually, an electronic monitor is used to check the frequency, duration, and strength of contractions. This monitor has a transducer that is placed over your abdomen with a belt. The contractions are transmitted and recorded by the monitor. The fetal heart rate may also be monitored at this time.

Other ways of assessing preterm labor may include the following:

  • cervical examination - an examination by a physician's gloved fingers of the cervix can help determine if the cervix has softened, shortened, thinned, or dilated (opened) - all signs of preterm labor.
  • ultrasound (with a vaginal transducer to measure the length of the cervix, or with an abdominal transducer to check the fetus and amniotic fluid levels).
  • testing for premature rupture of membranes (the amniotic sac).
  • testing for fetal fibronectin (FFN) - a protein that helps glue together the tissues of the placenta. FFN may be released when there is a disruption in these tissues or with infection. The protein is then found in cervical secretions where it can be sampled and tested.
  • testing for estriol - a hormone that is released prior to onset of labor, which is found in the blood and saliva.

Treatment for preterm labor:

Specific treatment for preterm labor will be determined by your physician based on:

  • your pregnancy, overall health and medical history.
  • extent of the condition.
  • your tolerance for specific medications, procedures or therapies.
  • expectations for the course of the condition.
  • your opinion or preference.

Treatment for preterm labor may include:

  • bedrest (either at home or in the hospital may be recommended).
  • hospitalization (as specialized personnel and equipment may be necessary).
  • tocolytic medications - medications to help slow or stop contractions. These may be given in an injection or intravenously. Tocolytic medications often used include terbutaline and magnesium sulfate.
  • corticosteroid medications - medications that may help mature the lungs of the fetus. Lung immaturity is a major problem of premature babies.
  • cervical cerclage - a procedure used to suture the cervical opening. Cerclage is used for women with an incompetent cervix. This is a condition in which the cervix is physically weak and unable to stay closed during pregnancy.
  • antibiotics (to treat infection).
  • delivery - if treatments do not stop preterm labor or if the fetus or mother is in danger, delivery of the baby may occur. Cesarean delivery may be recommended in certain cases.

Prevention of prematurity:

Because of the tremendous advances in the care of sick and premature babies, more and more babies are surviving despite being born early and being very small. However, prevention of early birth is the best way of promoting good health for babies.

Prenatal care is a key factor in preventing preterm births and low birthweight babies. At prenatal visits, the health of both mother and fetus can be checked. Because maternal nutrition and weight gain are linked with fetal weight gain and birthweight, eating a healthy diet and gaining weight in pregnancy are essential. Prenatal care is also important in identifying problems and lifestyles that can increase the risks for preterm labor and birth. Some ways to help prevent prematurity and to provide the best care for premature babies may include the following:

  • identifying mothers at risk for preterm labor.
  • prenatal education of the symptoms of preterm labor.
  • avoiding heavy or repetitive work or standing for long periods of time. which can increase the risk of preterm labor.
  • early identification and treatment of preterm labor.

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