These births account for 75% of newborn deaths not related to malformations. The dramatic decline in newborn mortality in the US in the past 30 years is due to significant improvements in newborn intensive care, not a reduction in the number of babies born early. It is most discouraging that the rate of preterm birth in this country has not changed since recordkeeping began in the 1950's.
What is preterm birth?
Preterm birth is defined as birth before the 37th week of gestation, calculated from the first day of the woman's last normal menstrual period. A baby is considered full term if born within 2 weeks of the "due date", (40 weeks after the last period). The smallest preterm babies (weighing below 1500 grams) aretwo hundred timesmore likely to die in the first year of life than babies born weighing greater than 2500 grams. Even if they survive, these very small infants are at 10 times greater risk of long term problems such as vision and hearing complications, chronic lung disease, cerebral palsy, and other neurological disorders.
What is preterm labor?
Preterm labor is defined as regular contractions of the uterus,plusa change in the amount of opening and thinning of the cervix before the 37th week of gestation. A woman's perception of her contractions varies, and studies have not shown that routinely examining the cervix during pregnancy is helpful in detecting preterm labor. Maternity care providers struggle with the diagnosis. Half of all women with a diagnosis of preterm labor (they have contractionsandcervical change) go on to full term pregnancy without any treatment. Twenty percent of women who don't meet the criteria for preterm labor (they have contractions, but their cervix doesn't change, for example), come back to deliver preterm anyway.
What causes preterm labor and birth?
Despite serious efforts to reduce preterm birth, there is little good news. Factors that start a normal, term labor are poorly understood, and preterm labor is more perplexing. Researchers have tried to identify the causes of preterm labor and birth, the women who are at risk, and ways to prevent or treat preterm labor. Very few clear answers have emerged.
Most often, the cause of preterm labor is unknown. Sometimes malformations of the uterus or cervix are associated with early delivery. Often these are unknown to the woman prior to becoming pregnant. Even if known, how much a uterine fibroid or unusually shaped uterus will affect the pregnancy is often difficult to predict.
One cause of preterm labor ispremature (before labor begins), preterm (before full term) rupture of membranes.It is not known why the fetal membranes rupture too early in some pregnancies. When the fluid around the baby leaks out, the baby and mother are exposed to infection. Labor usually occurs within a few days. Babies born too early face significant problems, and infection makes the situation worse.
Infections of the vagina, cervix, or uterushave been studied as possible causes of preterm rupture of the membranes. When infection is present in the vagina or cervix, toxins produced by the organism may weaken the membranes, making them more likely to leak or rupture. Inflammation from infections causes a local release of a substance known as prostaglandin. Prostaglandins are found throughout the body, and the substance is believed to have some role in the beginning of labor. Why some women have infections without early rupture of membranes or preterm labor is unknown. Organisms believed to increase the chances of early rupture of membranes include the gonorrhea, trichomonas, and beta-streptococcus organisms. Many sexually transmitted diseases are routinely screened for in pregnancy, and recent recommendations for beta-streptococcal infections have been published.
Who is at risk for preterm labor and birth?
Since certain factors seem to be associated with preterm birth (low socioeconomic status, nonwhite race, age under 18 or over 40, previous preterm labor or delivery, and underweight prior to pregnancy), there have been many attempts to develop a reliable way to screen women for their risk of delivering too early. Providing a risk "score" for women believed to be more likely to have a preterm birth results in one fourth of the pregnant population being identified as "high risk". But only 10% of babies are born preterm, so more than half of "high risk" mothers don't deliver preterm. Of the women who are identified as "low risk" during their pregnancy, more than half of them deliver preterm. The factor that most accurately predicts the likelihood of delivering too early is a history of a preterm birth in a prior pregnancy. This is not helpful for women pregnant for the first time. It is no wonder risk scoring has proved so disappointing.
How can preterm labor be prevented?
Obviously, if the causes of preterm labor are unclear, and the women who are at risk are hard to identify, designing a plan to prevent the problem is very difficult. Some of the approaches have included regular cervical exams in pregnancy (to detect early changes in the cervix), teaching women how to recognize uterine contractions, electronic monitoring for uterine contractions, and evaluation of a variety of naturally occurring chemical substances in the vagina or maternal blood stream. Since the signs and symptoms of preterm labor frequently overlap the normal symptoms of pregnancy, most prevention programs are not very effective.
A new test ...
Recent reports of a biochemical substance detectable in the vagina have shown some promise.Fetal Fibronectinis a special protein which has been identified in vaginal secretions in the early weeks of pregnancy, and again 1-2 weeks before labor begins. Studies have shown that the test for fetal fibronectin (a simple swab of vaginal fluid) is helpful in predicting preterm delivery, and the test may help predict the opposite problem - pregnancies which continue postterm. The test seems to be most helpful in predicting which of the women with a diagnosis of preterm labor (contractions plus change in the cervix) will actually deliver early, since up to 50% may continue to term with no treatment. Fetal fibronectin may also be helpful in predicting preterm labor in women who have no symptoms.
How is preterm labor treated?
How to treat preterm labor (or whether to treat at all) remains a question yet to be answered. Bedrest and intravenous fluids are believed to help stop contractions for some women, but clear benefit has not been shown. Treating preterm labor with medication has historically been unpleasant for the mother, at times dangerous, and has shown limited benefit in reducing numbers of preterm births.
Studies have not shown a clear improvement in the survival of preterm babies or how well they do later with long term use of drugs to stop contractions of the uterus (tocolytics). Side effects are very common and dangerous effects, though quite rare (fluid in the lungs, blood chemistry imbalances, heart problems, liver and kidney complications and even death) have been recorded.
Today, tocolytic drugs appear most helpful in delaying birth for a few days to a week. This time may allow transfer of the mother to a high risk center with capability to care for the preterm infant or the use ofsteroid drugsto speed up maturing of the baby's lungs. Babies between 24 and 34 weeks gestation clearly benefit when steroids are given to the mother before delivery. These infants have been shown to have fewer respiratory difficulties, the major problem of preterm birth, and therefore fewer complications from being born early. The best time for the steroid is 24 hours before birth and the effect lasts for one week after it is given. Advantages of using steroids when the amniotic membranes are ruptured or leaking is less clear. Antibiotics may be helpful with rupture of membranes, and medical studies are ongoing.
Preterm newborn survival has been shown to be greatest in high risk centers with neonatal intensive care units. Transportation of the mother while still pregnant is better than transporting the tiny newborn.
Reducing your risk of preterm birth
Because preterm labor and birth are so very hard to detect and prevent, early and consistent prenatal care is very important. Reducing exposure to sexually transmitted diseases, good nutrition and weight gain, quitting cigarette smoking and alcohol or drug use can also reduce your risk. Awareness of the signs and symptoms of preterm labor can help you identify changes from normal that may indicate a problem. In general, it is believed that early treatment is most beneficial.
What to look for
You might be considered more "at risk" for preterm labor or birth if you:
- Had a previous preterm labor or birth.
- Have an abnormally shaped uterus, or are a DES daughter.
- Had two or more pregnancy losses after the 13th week.
- Have an incompetent cervix or uterine fibroids.
- Are currently pregnant with twins or multiples.
- Have severe kidney or urinary tract infections.
- Have a placenta previa.
- Have too much or too little amniotic fluid.
Any "risk" for preterm labor is best evaluated by your caregiver - physician or nurse midwife.
The following signs may occur with preterm labor. They can also be a part of a very normal pregnancy. It is important for you to recognize what may be a change from your normal pregnancy experience.
- Uterine Contractions: tightening of the uterus which occurs more often than 4 times per hour. They will probably be painless. Report them to your caregiver if position changes, emptying your bladder and increasing your fluid intake do not make them less than 4 per hour within 1-2 hours. A pattern of contractions may be normal for you, and may increase a little toward the end of your pregnancy. If it is more than 3 weeks before your due date and there is a change in the contraction pattern, contact your caregiver.
- Menstrual-like cramps- may be normal, but feel your uterus for contractions.
- Low, dull backache- check for contractions.
- Pelvic pressure.
- Intestinal cramps, gas pains, diarrhea.
- Increase or change in vaginal discharge.
- A general feeling that something is not right.
What to do if you notice signs of preterm labor:
First, empty your bladder, then lie down on your left side to feel for contractions. Do not lie flat on your back. Place your fingertips on your uterus and indent all over with the tips of your fingers. A contraction feels firm all over the uterus, and may make the outline of the uterus easier to feel. Contractions gradually soften.Contractions may be painless!If you feel more than 4 contractions in one hour:
- rest on your side for an hour
- drink 2-3 glasses of water or juice
- if they do not become less frequent than 4 contractions per hour, call your caregiver. Don't think you are being a pest or complaining. It may be the best thing you ever do for your baby!
