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What are preterm labor and preterm birth?

You're in preterm labor, also known as premature labor, if you start having regular contractions that cause your cervix to start to open or thin out (called dilation and effacement) before you reach 37 weeks of pregnancy. If you deliver your baby before 37 weeks, it's called a preterm birth and your baby is considered premature.

About a quarter of all preterm births are intentional. For example, your medical team might decide to induce labor early or perform a cesarean section because you have a serious medical condition such as severe or worsening preeclampsia, or because your baby has stopped growing.

The rest are known as spontaneous preterm births. You may end up having a spontaneous preterm birth if you go into labor prematurely, if your water breaks early (called preterm premature rupture of the membranes or PPROM), or if your cervix dilates prematurely with no contractions (called cervical insufficiency).

About 12 percent of babies in the United States are born prematurely. This number has gone up over the years, partly because more women are pregnant with twins or higher multiples, who tend to arrive early. Preterm birth can cause health problems or can even be fatal for the baby if it happens too early. The more mature a child is at birth, the more likely he is to survive and the less likely he is to have health problems.

Premature babies born between 34 and 37 weeks generally do very well. If you go into labor before 34 weeks, your medical team may be able to delay your labor for a few days so your baby can be given corticosteroids to help his lungs and other organs develop faster, which greatly increases his chances of survival.

What causes spontaneous preterm birth?

Although the cause is often unknown, a variety of things can play a role in preterm birth:

• Certain genital tract infections, such as chlamydia, bacterial vaginosis, and trichomoniasis, are associated with an increased risk of preterm delivery. Substances produced by bacteria can weaken the membranes around the amniotic sac and cause it to rupture early. Even when the membranes remain intact, bacteria can get into the amniotic fluid or sac and cause preterm labor.

You might have been tested for sexually transmitted infections like chlamydia and gonorrhea at your first prenatal visit, and you would have been treated immediately if diagnosed. You might also have been screened for bacterial vaginosis (BV) if you had a previous preterm birth. Although some studies show that treating BV in the second and third trimesters reduces the risk of preterm labor in women with a history of preterm birth, other research shows it makes no difference. So experts don't agree on whether it's worthwhile to test pregnant women who don't have symptoms. (If you have symptoms of bacterial vaginosis, you'll be tested and treated with antibiotics, if needed.)

You probably won't be tested for trichomoniasis unless you have symptoms. That's because some research suggests that treating women for trichomoniasis during pregnancy actually increases the risk of preterm birth.

• Having a problem with the placenta, such as placenta previa or placental abruption.

• Having structural abnormalities of the uterus or cervix, such as a cervix that's shorter than 25 millimeters and that effaces or dilates without contractions (called cervical insufficiency).

• Having an excessively large uterus, which is often the case when you're pregnant with multiples or have too much amniotic fluid.

• Other conditions that may be related to preterm labor include certain chronic maternal illnesses, such as diabetes, sickle cell anemia, severe asthma, lupus, inflammatory bowel disease, and chronic active hepatitis; non-uterine infections, such as a kidney infection or pneumonia; abdominal surgery, such as having your appendix taken out; trauma to the abdomen; severe gingivitis (gum disease) and periodontitis (a gum infection that goes into the bone and other tissue that supports your teeth).

What are the risk factors for spontaneous preterm birth?

Although it's impossible to predict your chances of giving birth prematurely, you may be at an increased risk if you:

• Previously had a preterm delivery (The earlier in gestation your baby was born and the more spontaneous preterm births you've had, the higher the risk.)

• Are pregnant with twins or higher number multiples

• Are younger than 17 or older than 35

• Are African American (17.4 percent of African American babies are born prematurely)

• Don't gain enough weight during your pregnancy

• Were underweight before you got pregnant

• Are short

• Have had vaginal bleeding in more than one trimester

• Smoke, abuse alcohol, or use drugs (especially cocaine) during pregnancy

• Gave birth in the last 18 months (particularly if you gave birth within the last six months)

A few studies have found an association between high levels of stress and preterm birth. The theory is that severe stress can lead to the release of hormones that can trigger uterine contractions and preterm labor. Experts have also been studying occupational factors to see whether extremely physically demanding jobs or long working hours play a role.

One study showed that moms-to-be who had to stand for long periods (more than 40 hours a week) or had extremely tiring jobs were more likely to have preterm deliveries. Finally, some researchers are studying the possible effect of genetic factors on preterm birth because it seems to be more common in some families. They believe that genetics may explain to some degree the different rates seen among various races, even when other risk factors are taken into account.

Are there tests that can predict my chances of a preterm delivery?

Two screening tests are available for women who are having symptoms of preterm labor or are otherwise at high risk for it. Negative results are particularly useful because they can help you avoid unnecessary interventions and time in the hospital, and put your mind at ease. The American College of Obstetricians and Gynecologists doesn't recommend either test for all pregnant women because studies haven't shown them to be useful for women who aren't at high risk and have no symptoms.

Measuring the length of your cervix

Practitioners routinely check the length of your cervix at the first prenatal visit, so they can monitor changes as your pregnancy progresses. If your cervix is getting shorter in midpregnancy, that means it's beginning to efface (thin out) and you're at higher risk for preterm delivery. If you're at high risk for cervical insufficiency (because your cervix is abnormally short, for example), or if you later have symptoms that indicate your cervix is changing (such as pelvic pressure, backache, or increased mucus discharge), your practitioner may recommend an ultrasound to measure your cervix more accurately and look for signs that it's changing.

If the ultrasound shows that your cervix is starting to change, your practitioner will probably tell you to cut back on physical activity and work, to stop having sex, and to stop smoking if you haven't already. Depending on your situation and your baby's gestational age, you might have another ultrasound within the next few weeks.

If you're less than 24 weeks and your cervix is changing but you're not having any contractions, your practitioner may recommend a cerclage, a procedure in which she stitches a band of strong thread around your cervix to reinforce it and help hold it closed. However, there's considerable controversy about whether cerclage is effective enough in this situation to be worthwhile. (Women who seem to benefit from cerclage include those who've had three or more unexplained second-trimester losses or preterm births. If you're in this group, you're likely to get a cerclage at 13 to 16 weeks, before your cervix starts to change.)

Fetal fibronectin screening

This test is usually reserved for women who are having contractions or other symptoms of preterm labor, to help make a more accurate diagnosis. Fetal fibronectin (fFN) is a protein produced by the fetal membranes. If more than a small amount turns up in a sample of your cervical and vaginal secretions between 24 and 34 weeks of pregnancy, you're considered to be at higher risk for preterm delivery.

A positive test result might prompt your practitioner to give you drugs to stop labor for the short term and corticosteroids to help your baby's lungs mature faster. However, the test is actually more accurate at telling you when you won't deliver than when you will. If you have a negative fFN test result, you're highly unlikely to have a preterm delivery within the next two weeks. A negative result can put your mind at ease and help you avoid hospitalization or bedrest and medications that may have side effects.

Another technique, called home uterine activity monitoring (HUAM), is no longer thought to be useful in predicting preterm birth. To use it, you have to wear a sensor around your abdomen that records daily uterine activity. This system is expensive, and while your practitioner may prescribe it for individuals, experts agree that it has not helped reduce the preterm delivery rate in the United States.

Is there anything else I can do if I'm at high risk?

Take care of yourself. If you eat well, get plenty of rest, start your prenatal care early and see your practitioner regularly, manage your stress level, and pay attention to your hygiene and dental care, you're already doing a lot to ensure a healthy, full-term pregnancy. Take time to get to know the changes in your body during pregnancy. Spend some quiet time each day away from everyone else, so you can focus on your baby's movements and take note of any unusual aches or pressures.

Be aware of the signs of preterm labor mentioned below and let your practitioner know right away if you notice any of them. The most important development in preterm labor management in the last 50 years has been the use of corticosteroid medications to speed up the development of the baby's organs before birth. The earlier you discover you're in preterm labor, the more likely your baby will be able to benefit from this treatment.

Your practitioner might consult with a high-risk specialist (a perinatologist) or might refer you to one, particularly if you've had a preterm delivery before. If you've had a second trimester loss or a spontaneous preterm birth and are carrying only one baby, the specialist may consider treating you with a progesterone compound called 17 alpha hydroxyprogesterone caproate, or 17 P for short.

Studies have shown that weekly injections of this hormone starting in the second trimester and continuing until 36 weeks significantly reduced the risk of having another preterm birth for women in this situation. 17P is not yet available everywhere. The FDA has not yet approved it for manufacture by pharmaceutical companies, and only a limited number of pharmacies are set up to make it. Studies are under way to see if 17P will help reduce preterm deliveries in other high-risk groups, such as women carrying twins.

Other than that, there's not much you can do. Some practitioners will suggest bedrest, though there's no evidence that it will help prevent preterm birth.

What are the symptoms of preterm labor?

Call your midwife or doctor right away if you're having any of the following in your second or third trimester (before 37 weeks):

• An increase in vaginal discharge or a change in the type of discharge, meaning if it becomes watery, mucus-like, or bloody (even if it's pink or just tinged with blood)

• Any vaginal bleeding or spotting

• Abdominal pain, menstrual-like cramping, or more than four contractions in one hour (even if they don't hurt)

• An increase in pressure in the pelvic area (a feeling that your baby is pushing down)

• Low back pain, especially if you didn't previously have back pain

These symptoms can be confusing because some of them, such as pelvic pressure or low back pain, occur during normal pregnancies, too, and sporadic early contractions may just be Braxton Hicks contractions. But it's always better to be safe than sorry, so call your midwife or doctor right away.

What will happen if I start having preterm labor? If you have signs of preterm labor or think you're leaking amniotic fluid, call your practitioner, who will probably have you go to the hospital for further assessment. You'll be monitored for contractions (your baby's heart rate will be monitored at the same time) and examined to see if your membranes have ruptured. Your urine will be checked for signs of infection, and cervical and vaginal cultures may be taken, too. You might also be tested for fetal fibronectin.

If your water hasn't broken, your practitioner will do a vaginal exam to assess how much your cervix is dilated and effaced. Often a practitioner will also do an abdominal ultrasound to check the amount of amniotic fluid present and to confirm the baby's growth, gestational age, and position. Finally, some practitioners will do a vaginal ultrasound to double-check the length of your cervix and look for early signs of effacement. If all tests are negative, you and your baby appear healthy, your membranes haven't ruptured, and your cervix remains closed and uneffaced after a few hours of monitoring, you'll most likely be sent home.

Although different practitioners may manage the situation a little differently, there are some general guidelines. If you're less than 34 weeks pregnant and found to be in preterm labor, your membranes are intact, your baby's heart rate is reassuring, and you have no signs of a uterine infection or other problems (such as severe preeclampsia or signs of a placental abruption), your practitioner will attempt to delay your delivery.

First, you'll be put on an IV and given antibiotics to prevent group B streptococcal infection in your baby. This is done just in case a culture shows you're a carrier, as it takes 48 hours to get results. You'll most likely be given medication to try to stop contractions (this can usually delay delivery for two days to a week), as well as corticosteroids to speed up the development of your baby's lungs, intestines, and brain.

If you're in a small community hospital where special neonatal care is not available for a preterm infant, you'll be transferred to a larger institution at this point, if possible. You and your baby will be monitored throughout labor if it does continue.

If your water breaks before 37 weeks but you're not having contractions, your medical team may decide to wait for the onset of labor (which could happen within hours or could take up to a week in the hospital), to induce labor, or to try to delay labor. In any case, you'll be given antibiotics to protect against group B strep and other infections.

Experts differ on what to do in this situation. Waiting to deliver buys your baby more time to mature but increases your risk of infection, which could be dangerous for your baby. Of course, if you develop symptoms of infection or it's clear that your baby's in distress, they'll want you to deliver right away, often by cesarean section.

In most cases, if you're in premature labor after 34 weeks, you'll be allowed to deliver your baby. Babies born between 34 and 37 weeks of gestation who have no other health problems generally do fine. They may need a short stay in the neonatal nursery and may have a few short-term health issues, but in the long run, they usually do as well as full-term babies.