An ordinary pregnancy lasts 37 to 42 weeks, with 40 weeks being the average. Most babies arrive near their due date, give or take a week or two. However, about 12 percent of babies in the United States are born before the 37th week. This is known as preterm birth.
Risks to the baby. Babies do a lot of developing during the last trimester of pregnancy, and if they're born early, they face an uphill battle. Preterm birth is the leading cause of death among newborns. Those who survive are more likely than full-term babies to have lifelong health problems such as developmental delays, hearing loss, blindness, chronic lung disease, and cerebral palsy. About 25 percent of very premature infants (those born before 32 weeks' gestation) suffer significant, long-term impairment of brain development.
Your likelihood of a preterm birth. Researchers have identified some of the risk factors for premature births. A woman is more likely to have a premature baby if she:
- Has had a previous premature delivery.
- Is pregnant with more than one baby.
- Suffers from a chronic illness such as diabetes or hypertension.
- Was very overweight or underweight before pregnancy.
- Smokes cigarettes.
- Is African-American.
- Has had an infection such as bacterial vaginosis, a urinary tract infection, or sexually transmitted infections during pregnancy.
- Is under age 17 or over age 35.
- Has experienced severe chronic stress or anxiety during pregnancy.
- Became pregnant with the help of infertility treatments.
- Has particular or certain abnormalities in her cervix or uterus.
- Has experienced domestic violence during pregnancy.
Prevention. If you are at increased risk for preterm birth because you had a previous preterm birth, your doctor may recommend weekly progesterone injections known as 17P. In recent studies, administering weekly progesterone injections beginning at weeks 16-20 to women with a history of preterm birth reduced the chance of another preterm birth by as much as 33 percent. This medication is not for all women; talk to your doctor.
Warning signs. In some cases medical treatment can delay preterm labor and give a baby more time to grow before being born. Treatment works best when it is administered early, so watch for these signs of early labor. Even if you are experiencing only one of the following symptoms, call your doctor right away. It's better to be overcautious than to take the chance of letting premature labor continue without medical care:
- Contractions every 10 minutes or less.
- Fluid or blood coming from your vagina.
- A sense of pressure in the pelvis that feels as if your baby is pushing down.
- A low, dull backache or cramps that feel like menstrual cramps.
- A change in vaginal discharge from creamy white to thin and mucousy.
When you call the doctor, he or she will ask about your symptoms and your gestational age. (Remember to report the weeks.) He or she may ask you to come into the office or go to the hospital to be monitored and to have a cervical exam to see if your cervix is dilating. If you are having contractions with cervical change, then you are having preterm labor.
Medical interventions. If you have symptoms of premature labor, your doctor may order a fetal fibronectin (fFN) test, which measures the level of a certain protein in your cervical-vaginal secretions. A negative fFN test is a highly reliable predictor that delivery will not occur within the next two weeks. A positive fFN test is not nearly as reliable; you may deliver early, but then again you may not. There are no tests that accurately predict which women with preterm labor will have a preterm birth. Many times it is a nerve-racking wait-and-see situation.
Some doctors recommend bed rest to prevent preterm labor, although research does not show that bed rest actually helps to stave off premature labor. Despite the scarcity of solid evidence, however, most doctors are cautious and advise bed rest for preterm labor.
Although doctors can't stop preterm labor, they can administer tocolytics, a class of medications that can often slow down labor for two to three days. Although that might not sound like much time, it can make a difference: Even a few extra days in the uterus can increase a preterm baby's chance of healthy survival, especially at extremely early gestational ages (24-26 weeks). If you are at 24-34 weeks' gestation, you will probably be given corticosteroids, a medication that increases the amount of surfactant in the baby's lungs. Surfactant allows the baby to breathe easier and spend less time after birth on a ventilator. The baby needs to stay in utero for at least 48 hours after you receive corticosteroids to receive the drug's maximum benefit. If your water has broken, you may receive antibiotics to prevent group B strep infection and prolong in utero time.
Medical care after delivery. After birth a preterm baby goes to the neonatal intensive care unit (NICU), which contains medical equipment that helps the baby breathe, stay warm, take in nourishment, and receive care for health problems. In the NICU, a baby receives treatment from a neonatologist, a pediatrician who is specially trained to help premature babies. A preterm baby may spend anywhere from a few days to a few months in the NICU, depending on how early the baby was born and what health problems exist.
Choosing the right hospital. If you are at increased risk for preterm delivery, investigate your hospital's NICU. Hospitals are given designations that indicate the level of neonatal care they provide. A level 1 hospital has no neonatal intensive care unit; a level 3 hospital offers the most advanced care, with state-of-the-art equipment and the most highly trained staff. If your hospital is level 1, you may want to consider going to a different hospital. Also remember that half of all preterm births occur in women who are not at high risk. If you're not at high risk and plan to use a level 1 hospital, ask your obstetrician what will happen if you have preterm labor. If there is time to safely transport you with baby in utero to a level 3 hospital, that is the ideal situation.
Originally published in You & Your Baby: Pregnancy.
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