Preterm labor

Labor is a series of contractions in a pregnant woman's uterus that leads to the birth of a baby. During labor, the cervix -- the tip of the uterus that extends into the vagina -- effaces (thins) and dilates (opens) to allow the baby to move down the birth canal. Labor typically occurs between the end of week 37 through week 42 of pregnancy. When labor occurs after week 20 but before the end of week 37, it's called preterm (premature) labor.

Infants born at this time (premature infants) are not always ready to live on their own. They may be small and have serious difficulty breathing, eating and keeping warm. Eight to 10 percent of all babies born in the United States are born prematurely. Despite increased prevention efforts, the incidence of preterm birth has continued to rise during the past two decades.

If you're pregnant, it's essential to know the symptoms of preterm labor so you can seek treatment as soon as possible. This is the best way to prevent premature birth. If premature birth can't be avoided, early treatment may delay the birth long enough to create more favorable conditions for the baby.


Causes/associated factors
The exact cause of most cases of preterm labor is unknown. A number of factors increase the risk of preterm labor, however. The most important risk factor is a previous preterm labor or delivery.
Other risk factors include:

a previous second trimester miscarriage or abortion
chronic health problems (such as heart disease, kidney disease, diabetes or high blood pressure)
being younger than 18 or older than 40
being underweight or weighing less than 100 pounds before pregnancy
lack of prenatal care
smoking
substance abuse (including alcohol, cocaine or other street drugs)
psychological stress
uterine abnormalities
exposure to diethylstilbestrol (DES) before birth (DES is a synthetic estrogen that was routinely given to pregnant women in the United States from 1938 to the early 1970s. It's been associated with tubal abnormalities.)
cervical incompetence (a common symptom among mothers who were exposed to DES in utero)
Other factors that may be associated with preterm labor include:

early rupture of the membranes
infected or excessive amniotic fluid (the fluid that surrounds and protects the fetus in the womb)
vaginal, cervical, uterine or urinary tract infections
syphilis, gonorrhea, bacterial vaginosis, group B streptococcus, chlamydia, trichomoniasis and other infections, including pneumonia, malaria and typhoid fever
uterine overdistention caused by a multiple pregnancy (twins or triplets, for example)
placental abnormalities, such as placenta previa (a condition in which the placenta blocks the birth canal) or abruptio placenta (early separation of the placenta from the uterus)
bleeding after the first trimester
fetal abnormalities, such as a neural tube defect (affecting the brain and spinal cord)
surgical procedures during pregnancy, especially those done close to the uterus (such as removal of the appendix or an ovarian tumor)
It's important to note that 50 percent of all women who develop preterm labor have no identifiable risk factors.


Signs/symptoms
Symptoms of preterm labor, which may be subtle and develop slowly, may include:
painful or painless contractions
menstrual-like cramping or general abdominal cramping
backache, which may be dull and intermittent
feeling of pelvic pressure, as if the baby is pushing into your pelvis
increase or change in the type of vaginal discharge, such as watery, bloody or containing mucus
leaking of fluid (premature rupture of membranes)
diarrhea

Diagnosis
If detected early, treatment for preterm labor may prevent or delay an early delivery. You can help with an early diagnosis by learning the symptoms of preterm labor and monitoring yourself regularly for contractions after the 20th week of pregnancy. (See details below.) Contact your doctor immediately if you experience any symptoms of preterm labor, you detect six or more contractions in an hour, or you have contractions less than 10 minutes apart. Even if you can't identify specific symptoms of preterm labor but are concerned it may be occurring, contact your doctor.
Later in pregnancy, it's common to feel your uterus tighten (called Braxton Hicks contractions) or experience false labor. In fact, it's often difficult to determine the difference between true and false labor. To determine if preterm labor has actually begun, your doctor may:

Do a pelvic exam to detect any changes (dilation or effacement) in the cervix. This may need to be done more than once.
Do a transvaginal ultrasound (an ultrasound -- using sound waves to created an image of internal body parts -- done through your vagina) to identify changes in cervical length.
Monitor the baby's heartbeat, as well as uterine contractions.
Depending on the circumstances, other tests may also be needed. An ultrasound can help your doctor determine the age and position of the fetus and check for congenital anomalies. Amniocentesis (a procedure in which amniotic fluid is withdrawn for examination) can help the doctor evaluate the baby's lung maturity and check for infection. Lab tests of your blood, urine and vaginal fluid may be done to check for infection, and your vaginal fluid may be evaluated to check for rupture of the membranes.

Two specific tests have been approved by the U.S. Food and Drug Administration (FDA) to help predict preterm delivery. The fetal fibronectin (fFN) test checks cervical secretions for fetal fibronectin (a substance that may be present when the placenta begins to detach from the uterine wall). If the test is positive, there is a risk of preterm delivery within seven days. If it's negative, delivery will probably not occur within the next seven to 14 days.

The salivary estriol (SalEst) test measures the amount of the hormone estriol found in your saliva. The amount of this hormone in your saliva typically increases three to five weeks before delivery. The American College of Obstetricians and Gynecologists (ACOG) is not currently recommending this test due to a high number of false predictions of preterm labor, however.


Treatment
Finding an effective treatment for preterm labor has been hindered by a lack of complete understanding of the factors that cause normal labor. While researchers are studying the most effective treatments, controversy over the best treatment for preterm labor continues.
In the meantime, treatment varies depending on the cause of the preterm labor, the age and maturity of the baby, and whether you or the baby is in danger. To prevent or postpone premature labor or delivery, the doctor may prescribe bedrest, lying on your side. Extra fluids are important, and any infections will be treated. You may also be given medication to relax the uterus and stop contractions, such as magnesium sulfate, ritodrine, terbutaline, indomethacin or nifedipine. In some cases, cerclage (a suture used to support the cervix) may be recommended.

Once preterm labor is stopped, it may be possible for you to return home if you can get the amount of rest you need to help prevent a recurrence of labor. In other situations, you may need to remain in the hospital until delivery.

In some situations, it may be necessary to deliver the baby early or do a cesarean section (C-section, delivery of the baby through an incision in the abdomen). Sometimes, a delay of at least 48 hours may lead to a more favorable outcome for the baby. During this time, you may be given a corticosteroid medication that accelerates the baby's lung development and decreases the risk of lung disease. You may also be treated with preventive antibiotics. If necessary, you may also be transferred to a hospital that has a neonatal intensive care unit (NICU), where the baby can receive specialized care after birth.


Risks
Medications to stop contractions can cause varying side effects for both mother and baby, such as a rapid heart rate. Discuss the specific side effects with your doctor. Together, you and your doctor must weigh the risks of the medication with the benefits that may be gained by stopping the preterm labor.

Complications
Preterm birth is the cause of nearly two-thirds of all newborn deaths not due to congenital malformations. The smaller the infant, the greater the risk. Serious complications of prematurity may include:
respiratory difficulty (such as apnea, respiratory distress syndrome, bronchopulmonary dysplasia or chronic lung disease)
heart and blood circulation problems (such as patent ductus arteriosus, slow heart rate or low or high blood pressure)
brain damage (such as intraventricular hemorrhage or seizures)
visual impairment (such as retinopathy)
hearing impairment
infection (sepsis)
intestinal problems
jaundice (yellowing of the skin and whites of the eyes)
low blood sugar
low body temperature
cerebral palsy (a condition that affects muscle control; people who have cerebral palsy may not be able to walk, talk, eat or play normally)
poor school performance
behavior problems

Prevention
If you're pregnant, it's essential to know the symptoms of preterm labor so you can seek treatment as soon as possible. After the 20th week of pregnancy, regularly check for contractions. Lie down comfortably on your side and place your hands flat on your abdomen with your fingers spread apart. When you're having a contraction, you'll feel the uterus hardening or tightening up like a flexed muscle. As the contraction ends, your uterus will gradually soften. Remember that early contractions aren't necessarily painful.
If you feel contractions, time them by measuring the amount of time between the beginning of one contraction and the beginning of the next one. Contact your doctor immediately if your detect six or more contractions in an hour or contractions are less than 10 minutes apart. If you have a history of rapid labor (six hours or less), contact your doctor at the first sign of contractions.

During pregnancy, keep these general preventive measures in mind.

Seek regular prenatal care throughout your pregnancy.
Eat healthfully, and take prenatal vitamins if recommended by your doctor.
Drink plenty of fluids to prevent dehydration.
Don't drink alcohol, smoke or take street drugs.
Take only the medications recommended by your doctor.
Avoid prolonged standing and overexertion. (If your job includes prolonged standing, exertion, lifting, climbing or bending below the waist, consult your doctor. You may need to modify your work as your pregnancy progresses.)
Get as much rest as possible during the last trimester.
Decrease stress as much as you can.
Report signs of a urinary infection (such as the need to urinate often or a burning sensation during urination) or vaginal infection (such as vaginal itching or pain) to your doctor.
If you have any risk factors for preterm labor, you may need more prenatal visits (possibly every one to two weeks after week 22 of the pregnancy) and extra rest. Depending on the circumstances, your doctor may also suggest bedrest. In addition, you may be asked to decrease or avoid sexual stimulation, including sexual intercourse, orgasm and breast stimulation. (If sex is allowed, you may be asked to use a condom to decrease the possibility of infection.) If you have a weak or incompetent cervix or your doctor suspects you do, he or she may recommend a cerclage.

Some doctors recommend home uterine activity monitoring (HUAM), although it has not been shown to significantly lower the rate of preterm birth. With this type of monitoring, you wear a monitoring device on your abdomen at specified times during the day. The device can record contractions you may not be able to detect on your own. This information is then transmitted automatically through the phone line to your doctor for analysis.

Finally, a recent study supervised by the National Institutes of Health found that the hormone progesterone may reduce the number of premature births for women in high-risk pregnancies. If you're at risk for preterm labor, discuss the possible use of progesterone with your doctor.