Low Birthweight

• Premature birth: Babies born before 37 completed weeks of pregnancy are called premature or preterm. About 67 percent of low-birthweight babies are premature (1). The earlier a baby is born, the less it is likely to weigh and the less developed its organs will be. Very low-birthweight babies (those who weigh less than 3 pounds, 5 ounces or 1,500 grams) have the highest risk of health problems. Some premature babies born near term do not have low birthweight, and they may have only mild or no health problems as newborns.
  
• Small-for-date babies (also called small-for-gestational age or growth-restricted): These babies may be full-term but are underweight. Some of these babies are healthy, even though they are small. They may be small simply because their parents are smaller than average. Others have low birthweight because something slowed or halted their growth in the uterus.

Some babies are both premature and growth-restricted. These babies are at high risk for health problems.

What causes low birthweight?
Preterm labor frequently results in the birth of a premature, low-birthweight baby. The causes of preterm labor are not thoroughly understood. However, we do know that women with these risk factors are at increased risk of delivering prematurely (2):

• Had a premature baby in a previous pregnancy
• Are pregnant with twins or other multiples
• Have certain abnormalities of the uterus or cervix

Other factors that may contribute to premature birth and/or fetal growth restriction include:

• Birth defects: Babies with certain birth defects are more likely to be small for date because genetic conditions or environmental factors may limit normal development (3, 4).
  
• Chronic health problems in the mother: Maternal high blood pressure, diabetes, heart, lung and kidney problems sometimes can reduce birthweight (3).
  
• Smoking: Pregnant women who smoke cigarettes are nearly twice as likely to have a low-birthweight baby as women who do not smoke (5). Smoking slows fetal growth and increases the risk of premature delivery (5).
  
• Infections in the mother: Certain infections, especially those involving the genito-urinary tract, may increase the risk of preterm delivery (2).
  
• Infections in the fetus: Infection with certain viruses, including cytomegalovirus, rubella and chickenpox, can slow fetal growth and cause birth defects (3, 4).
  
• Alcohol and illicit drugs: Alcohol and illicit drugs can limit fetal growth and can cause birth defects (3, 4). Some drugs, such as cocaine, also may increase the risk of premature delivery.
  
• Placental problems: Placental problems can reduce flow of blood and nutrients to the fetus, limiting growth. In some cases, a baby may need to be delivered early to prevent serious complications in mother and baby.
  
• Inadequate maternal weight gain: Women who gain too few pounds during pregnancy increase their risk of having a low-birthweight baby (3). Women of normal weight should usually gain 25 to 35 pounds during pregnancy.
  
• Socioeconomic factors: Low income and lack of education are associated with increased risk of having a low-birthweight baby, although the underlying reasons for this are not well understood. Black women and women under 17 and over 35 years of age are at increased risk (2, 3).

What can a woman do to reduce her risk of having a low birthweight baby?
There are some steps a woman can take to reduce her risk of having a low-birthweight baby. A woman who is planning pregnancy should see her health care provider for a pre-conception check-up. Her provider can help make sure she is as healthy as possible before she conceives. At this visit the provider can screen her for certain infections, make sure her vaccinations are up-to-date, and discuss her health habits and nutrition. The provider can make sure any medications the woman takes are the safest possible choices during pregnancy. A preconception visit is especially important for women with chronic health conditions, such as high blood pressure and diabetes. Good control of these disorders, starting before pregnancy, reduces the risk of low birthweight and other pregnancy complications.

A woman should stop smoking before she becomes pregnant and remain smoke-free throughout pregnancy. At a preconception visit, a woman's health care provider can refer her to a smoking-cessation program or suggest other ways to help her quit.

Once a woman is pregnant, she should get early and regular prenatal care. When women receive adequate prenatal care, health care providers can identify many problems early. This allows treatment that may reduce the risk of having a low-birthweight baby.

All women who could become pregnant should take a daily multivitamin containing 400 micrograms of folic acid, starting before pregnancy. When taken before and early in pregnancy, folic acid helps prevent certain serious birth defects of the brain and spine. When taken throughout pregnancy, folic acid also may help reduce the risk of having a premature and low-birthweight baby (6).

A woman who suspects that she is developing preterm labor should call her health care provider immediately. Her provider may want to examine her and do some tests to see if she really is in labor. If she is in labor, the provider may give her a medication (called a tocolytic) to try to delay or stop delivery. These drugs are most effective when given early in labor. Tocolytics often postpone delivery for only a day or two, but even such a short delay can make a difference in the baby's health.

Women who have already had a premature baby may benefit from treatment with a hormone called progesterone. Recent studies show that this treatment appears to reduce their risk of having another premature baby by about one-third (7, 8).

How is fetal growth restriction treated?
About 10 percent of fetuses are considered growth-restricted (3, 4). A health care provider may suspect fetal growth restriction if the mother's uterus is not growing at a normal rate. This can be confirmed with a series of ultrasound examinations that monitor how quickly the fetus is growing. In some cases, fetal growth can be improved by treating any condition in the mother (such as high blood pressure) that may be a contributing factor. 

The provider will closely monitor the well-being of a growth-restricted fetus using ultrasound and fetal heart rate monitoring. If these tests show that the baby is having problems, the baby may need to be delivered early.

What medical problems are common in low-birthweight babies?
Low-birthweight babies are more likely than babies of normal weight to have health problems during the newborn period. Many of these babies require specialized care in a neonatal intensive care unit (NICU). Serious medical problems are most common in babies born at very low birthweight.

• Respiratory distress syndrome (RDS): About 23,000 babies a year—most of whom were born before the 34th week of pregnancy—suffer from this breathing problem (1). 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. Babies with RDS also may need additional oxygen and mechanical breathing assistance to keep their lungs expanded. The sickest babies may temporarily need the help of a respirator to breathe for them while their lungs mature.
  
• Bleeding in the brain (called intraventricular hemorrhage or IVH): Bleeding in the brain occurs in some very low- birthweight babies, usually in the first three days of life. Brain bleeds usually are diagnosed with an ultrasound examination. Most are mild and resolve themselves with no or few lasting problems. More severe bleeds can cause pressure on the brain that can lead to brain damage. 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 common in premature babies. Before birth, a large artery called the ductus arteriosus lets the blood bypass the baby's nonfunctioning lungs. The ductus normally closes after birth so that blood can travel to the lungs and pick up oxygen. When the ductus does not close properly, it can lead to heart failure. 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 doesn't work.
  
• Necrotizing enterocolitis (NEC): This potentially dangerous intestinal problem usually develops two to three weeks after birth. It can lead to feeding difficulties, abdominal swelling and other complications. Babies with NEC are treated with antibiotics and fed intravenously (through a vein) while the bowel heals. In some cases, surgery is necessary to removed damaged sections of intestine.
  
• Retinopathy of prematurity (ROP): ROP is an abnormal growth of blood vessels in the eye that can lead to vision loss. It occurs mainly in babies born before 32 weeks of pregnancy. Most cases heal themselves with little or no vision loss. In severe cases, the ophthalmologist (eye doctor) may treat the abnormal vessels with a laser or with cryotherapy (freezing) to preserve vision.

Can medical problems in low-birthweight, premature newborns be prevented?
When a provider suspects that a woman may deliver before 34 weeks of pregnancy, she may suggest treating the mother with corticosteroid drugs. Corticosteroids speed maturation of the fetal lungs and significantly reduce the risk of RDS, IVH, necrotizing enterocolitis and infant death. These drugs, which are given by injection (a shot), are most effective when administered at least 24 hours before delivery. Treatment with tocolytic drugs to delay labor can give the health care provider time to treat the pregnant woman with corticosteroids. The provider also can arrange for delivery in a hospital with a NICU that can give specialized care to a premature, low-birthweight infant.

Is the March of Dimes supporting research on low birthweight?
The March of Dimes has long supported research on low birthweight and the related issue of prematurity. In 2005, the March of Dimes awarded approximately $2 million for a three-year period to six grantees as part of the Prematurity Research Initiative, which aims to learn more about the causes of prematurity. These grantees are exploring the role of genes, uterine muscle activity, cervical changes and the lung protein surfactant in triggering preterm labor, which may lead to better ways to prevent or treat it.

Other grantees are seeking to improve the treatment for premature, low-birthweight babies. For example, some are attempting to develop treatment that can help prevent brain damage and cerebral palsy in premature infants. Others are seeking to develop improved treatments for PDA and ROP.

The March of Dimes supports research related to smoking cessation during pregnancy and the link between smoking and low birthweight. The March of Dimes also promotes the health benefits of smoking prevention and cessation by providing educational materials for consumers, promoting evidence-based smoking-cessation methods, and supporting projects that increase smoking-cessation services available to pregnant women who smoke.