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 accompanied by cervical changes
Rupture of the amniotic sac (membranes)
Cervical dilatation (opening of the cervix)
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:
Preeclampsia (high blood pressure of pregnancy, which increases the risk of preterm delivery)
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)
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.
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.
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
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
Difficulty feeding (many are unable to coordinate suck and swallow before 35 weeks gestation)
Necrotizing enterocolitis (NEC)--a serious disease of the intestine common in premature babies
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
Vaginal discharge of blood, mucus, or water
If you notice any symptoms of preterm labor, be sure to call your doctor as soon as possible.
The symptoms of preterm labor may resemble other medical conditions. Always consult your doctor 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 and duration 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 health care provider'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)
Testing for premature rupture of membranes (the amniotic sac)
Testing for fetal fibronectin (FFN)--a protein found between the fetal membranes and uterine lining. 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.
Treatment for preterm labor
Specific treatment for preterm labor will be determined by your doctor 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 under the skin or intravenously (IV). Tocolytic medications often used include indomethacin or nifedipine.
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 may increase the risk of preterm labor
Early identification and treatment of preterm labor
Some women at high risk for preterm birth may be candidates for treatment with the hormone progesterone. This hormone and its derivative, 17-alpha hydroxyprogesterone, are naturally produced by the placenta during pregnancy. Recent studies have shown that progesterone supplements help reduce the risk for preterm birth in women who had a previous spontaneous preterm birth. More research is needed for this and other ways to help reduce the incidence of prematurity.