The Facts About Preterm Birth
Most pregnancies last around 40 weeks. Babies born between 37 and 42 weeks of pregnancy are called full term. Babies born before 37 completed weeks of pregnancy are called premature or preterm. About 12 percent of babies in the United States are born preterm. Of those, the majority (84 percent) are born between 32 and 36 weeks of gestation. About 10 percent are born between 28 and 31 weeks of gestation, and about 6 percent are born at less than 28 weeks of gestation.
All babies born preterm are at risk for serious health problems, but those born earliest are at greater risk of medical complications, long-term disabilities and death. Fortunately, advances in obstetrics and neonatology, the branch of pediatrics that deals with newborns, have improved the chances for survival for even these smallest babies.
Babies born preterm face a greater risk of serious health problems for several reasons. The earlier a child is born, the less she will weigh, the less developed her organs will be, and the more complications she is likely to face. These babies may require care in a neonatal intensive care unit (NICU), which has specialized medical staff and equipment that can deal with the multiple problems faced by premature infants. Very premature babies also have the highest risk of death and lasting disabilities, such as mental retardation, cerebral palsy, lung and gastrointestinal problems, and vision and hearing loss.
Not only are premature babies often small and sick, but they may look and behave very differently than full-term babies. For example, their skin may be thin and wrinkled, and their heads may look too large for their bodies. But these babies look the way they should at their stage of development, and will begin to appear and act more like full-term babies as they continue to develop and grow. Throughout their first year of life, these babies should be evaluated according to their adjusted age (which takes their prematurity into account).
What causes preterm birth?
A baby may be delivered preterm after a doctor induces labor due to pregnancy complications or health problems in the mother. However, most preterm births are a result of spontaneous preterm labor (which may follow spontaneous premature rupture of the membranes or PROM—the sac inside the uterus that holds the baby breaks too soon).
The causes of preterm labor and PROM are not fully understood, but the latest research suggests that many cases are triggered by the body’s natural response to certain infections, including infections involving the amniotic fluid and fetal membranes. However, in nearly half of all cases, the doctor cannot determine why a woman delivered preterm. And, at this time, there often is little the doctor or the pregnant woman can do to prevent preterm labor.
Which women are at increased risk of preterm delivery?
Any woman can deliver prematurely, but some women are at greater risk than others. Researchers have identified some risk factors, but experts still can’t predict which women will delivery prematurely.
Studies show that a woman is at high risk of preterm birth if she:
- Has had a previous preterm birth
- Is pregnant with twins, triplets or more
- Has certain uterine or cervical abnormalities
Researchers also have identified other risk factors. For instance, African-American women, women younger than 17 or older than 35, and poor women are at greater risk than other women. Certain lifestyle and environmental factors may put a woman at greater risk of preterm labor. These include: late or no prenatal care, smoking, drinking alcohol, using illegal drugs, exposure to the medication diethylstilbestrol (DES), domestic violence (including physical, sexual or emotional abuse), lack of social support, stress, and long working hours with long periods of standing.
Certain medical conditions during pregnancy also may increase the likelihood that a woman will have preterm labor. These include: infections (including urinary tract, vaginal, sexually transmitted and possibly other infections), diabetes, high blood pressure, clotting disorders (thrombophilia), bleeding from the vagina, certain birth defects in the baby, being pregnant with a single fetus after in vitro fertilization (IVF), being underweight before pregnancy, obesity, and short time period between pregnancies (less than 6-9 months between birth and the beginning of the next pregnancy).
What medical complications are common in premature babies?
There are a number of complications that are more likely in premature than full-term babies. While babies born near term may have few or none of these problems, babies born before 32 to 34 weeks gestation may have a number of complications. In some cases, these complications may be fairly mild while, in other cases, they are severe and may lead to long-term medical problems or even death.
- Respiratory distress syndrome (RDS). About 24,000 babies a year - most of whom were born before the 34th week of pregnancy - suffer from this breathing problem. Babies with RDS lack a protein called surfactant that keeps small air sacs in the lungs from collapsing. Treatment with surfactant helps affected babies breathe more easily. Since treatment with surfactant was introduced in 1990, deaths from RDS have been reduced by about two-thirds.A doctor may suspect a baby has RDS if she is struggling to breathe; a lung X-ray and blood tests often confirm the diagnosis. Babies with RDS may need additional oxygen and mechanical breathing assistance to keep their lungs expanded. They may receive a treatment called continuous positive airway pressure (CPAP), which delivers pressurized air to the baby’s lungs. The air may be delivered through small tubes in the baby’s nose, or through a tube that has been inserted into his windpipe. CPAP helps a baby breathe, but does not breathe for him. The sickest babies may temporarily need the help of a respirator to breathe for them while their lungs mature. They also may be treated with a gas called nitric oxide, which can improve breathing by helping blood vessels in the lungs relax.
- Apnea. Premature babies sometimes stop breathing for 20 seconds or more. This interruption in breathing is called apnea, and it may be accompanied by a slow heart rate. Premature babies are constantly monitored for apnea. If the baby stops breathing, a nurse will stimulate the baby to start breathing by patting him or touching the soles of his feet.
- Intraventricular hemorrhage (IVH). Bleeding in the brain occurs in some very low birthweight babies, with the most premature babies at highest risk. The bleeds usually occur in the first three days of life and generally are diagnosed with an ultrasound examination. Most brain bleeds are mild and resolve themselves with no or few lasting problems. More severe bleeds can cause the fluid-filled structures (ventricles) in the brain to expand rapidly, causing pressure on the brain that can lead to brain damage (such as cerebral palsy, learning and behavioral problems). In such cases, surgeons may insert a tube into the brain to drain the fluid and reduce the risk of brain damage. In milder cases, drugs sometimes can reduce fluid buildup.
- Patent ductus arteriosus (PDA). PDA is a heart problem that is commonly seen in premature babies. Before birth, a large artery called the ductus arteriosus lets the blood bypass the lungs because the fetus gets its oxygen through the placenta. The ductus normally closes soon after birth so that blood can travel to the lungs and pick up oxygen. In premature babies, the ductus may not close properly, which can lead to heart failure and lack of oxygen to the organs. PDA can be diagnosed with a specialized form of ultrasound (echocardiography) or other imaging tests. Babies with PDA are treated with a drug that helps close the ductus, although surgery may be necessary if the drug does not work.
- Necrotizing enterocolitis (NEC). Some premature babies develop this potentially dangerous intestinal problem (usually 2 to 3 weeks after birth), which leads to feeding difficulties, abdominal swelling and other complications. It is believed that the bowel may become damaged when its blood supply is decreased, and bacteria that are normally present in the bowel invade the damaged area, causing more damage. When tests (including X-rays and blood tests) show that a baby has NEC, she will be given antibiotics and fed intravenously while her bowel heals. In some cases, surgery is necessary to remove damaged sections of the intestine.
- Retinopathy of prematurity (ROP). ROP, an abnormal growth of blood vessels in the eye, occurs mainly in babies born before 32 weeks of pregnancy. It can lead to bleeding and formation of scars that can damage the retina of the eye, sometimes resulting in vision loss and blindness. Babies with mild ROP - which is diagnosed during an examination by an ophthalmologist (eye doctor) - usually require no treatment because, in most cases, the eyes heal by themselves with little or no vision loss. In more severe cases, the ophthalmologist may treat the abnormal vessels with a laser or with cryotherapy (freezing) to protect the retina and preserve vision.
- Jaundice. Premature babies are more likely than full-term babies to develop jaundice because their livers are too immature to remove a waste product called bilirubin from the blood. In addition, premature infants may be more sensitive to the ill effects of excess bilirubin. Babies with jaundice have a yellowish color to their skin and eyes. Jaundice often is mild and usually is not harmful; however, if the bilirubin level gets too high, it can cause brain damage. This generally can be prevented because blood tests will show when bilirubin levels are too high, so the baby can be treated with special lights (phototherapy) that help the body eliminate bilirubin. Occasionally, a baby may need a blood transfusion.
- Anemia. Premature infants often are anemic, which means they do not have enough red blood cells. Normally, the fetus stores iron during the later months of pregnancy and uses it late in pregnancy and after birth to make red blood cells. Infants born too soon may not have had enough time to store iron. Babies with anemia tend to develop feeding problems and grow more slowly; anemia also can worsen any heart or breathing problems. Anemic infants may be treated with dietary iron supplements, drugs that increase red blood cell production or, in severe cases, blood transfusion.
- Chronic lung disease (also called bronchopulmonary dysplasia). Chronic lung disease most commonly affects premature infants who require ongoing treatment with supplemental oxygen at 36 weeks postmenstrual age (after conception). These babies develop fluid in the lungs, scarring and lung damage, which can be seen on an X-ray. Affected babies are treated with medications that make breathing easier, and are slowly weaned from the ventilator. Their lungs usually improve over the first two years of life. However, many children develop chronic lung disease resembling asthma.
- Infections. Premature babies have immature immune systems that are inefficient at fighting off bacteria, viruses and other organisms that can cause infection. Serious infections that are commonly seen in premature babies include pneumonia (lung infection), sepsis (blood infection), and meningitis (infection of the membranes surrounding the brain and spinal cord). Babies can contract these infections at birth from their mothers or they may become infected after birth. Infections are treated with antibiotics or antiviral drugs.
What is the outlook for babies born at less than 28 weeks?
Fewer than 1 percent of babies in this country are born this early, but these babies have the most complications. Most of these babies are born at very low birthweight (less than 3 pounds, 4 ounces). Those born at less than 26 weeks are likely to weigh only 1 to 2 pounds. Almost all will require treatment with oxygen, surfactant, and mechanical assistance to help them breathe. These babies are too immature to suck, swallow and breathe at the same time, so they must be fed through a vein (intravenously) until they develop these skills. They often cannot yet cry (or you cannot hear them due to the tube in their throat) and they sleep most of the day. These tiny babies have little muscle tone and most move very little.
Babies born at this time look very different than full-term babies. Their skin is wrinkled and reddish-purple in color, and is so thin that you can see the blood vessels underneath. Their face and body are covered in soft hair called lanugo. Because these babies have not had time to put on fat, they appear very thin. Most likely, their eyes are closed and they have no eyelashes.
These babies are at high risk for one or more of the complications discussed above. However, most babies born after about 26 weeks gestation do survive to one year (about 80 percent at 26 weeks and about 87 percent at 27 weeks), although they may face an extended stay in the NICU. Unfortunately, about 20 to 40 percent of the very lowest birthweight babies develop serious lasting disabilities.
What about babies born at 28 to 31 weeks gestation?
These babies look quite similar to babies born earlier, although they are larger (usually between 2 and 5 pounds) and even more likely to survive (about 90 to 95 percent). Most require treatment with oxygen, surfactant, and mechanical assistance to help them breathe. Some of these babies can be fed breast milk or formula through a tube placed through their nose or mouth into the stomach, although others will need to be fed intravenously.
Some of these babies can cry. They can move more, although their movements may be jerky. A baby born at this time can grasp your finger. These babies can open their eyes and they begin to stay awake and alert for short periods.
Babies born at 28 to 31 weeks are at risk for some of the complications discussed above; however, when complications occur, they may not be as severe. Babies born with very low birthweight remain at risk for serious disabilities.
What about babies born at 32 to 35 weeks gestation?
More than 98 percent of babies born at this time survive. Most weigh between 3 and 7 pounds, and most appear thinner than full-term babies. Some can breathe on their own, and many others just need supplemental oxygen to help them breathe. Some can be breast- or bottle-fed, although babies born at less than 34 weeks or having breathing difficulties will probably need tube-feeding. Babies born after about 34 weeks are unlikely to develop serious disabilities resulting from premature birth, though they may remain at increased risk of subtle learning and behavioral problems.
Are babies born at 36 weeks gestation at risk of medical problems?
Most babies born at this time require little or no special care after birth, and they are nearly as likely as full-term babies to survive. They usually weigh between 4 and 8 pounds, and may still appear thinner than full-term babies. Some will experience mild problems, such as breathing difficulties or jaundice, but most will make a quick recovery. Most of these babies can be breast- or bottle-fed, although some (especially those with mild breathing problems) may need tube-feeding for a brief time. These babies are very unlikely to develop serious disabilities resulting from premature birth.
How can a woman reduce her risk of preterm delivery?
A woman may be able to reduce her risk of preterm delivery by visiting her health care provider before pregnancy and, once pregnant, seeking early and regular prenatal care. A pre-pregnancy visit is especially crucial for women with chronic disorders such as diabetes and high blood pressure, which sometimes can contribute to preterm birth. When a woman receives adequate prenatal care, problems usually can be identified early and treated, to reduce the risk of preterm birth. A 1996 study suggested that consuming the recommended amount of folic acid throughout pregnancy may reduce the risk of preterm birth. A woman should avoid alcohol, smoking and illicit drugs beginning before pregnancy and throughout pregnancy.
Can medical problems in premature newborns be prevented?
When a doctor suspects that a woman may deliver preterm, he or she may suggest treatment with corticosteroid drugs. Corticosteroids speed maturation of fetal lungs and significantly reduce the risk of RDS, IVH, necrotizing enterocolitis and infant death. These drugs are given by maternal injection and are most effective when administered at least 24 hours before delivery. Her doctor also may suggest treatment with medications (called tocolytics) that may postpone labor (though often not for more than a couple of days). Even this short delay can give the doctor time to treat the pregnant woman with corticosteroids and arrange for delivery in a hospital with a NICU that can give appropriate care to a premature infant, which could make a life-saving difference for her baby.
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