Prematurity or preterm birth refers to the birth of a baby before the thirty-seventh week of pregnancy. A normal pregnancy lasts between thirty-eight and forty-two weeks after conception. Babies born after forty-two weeks are called post-term babies.
Prematurity is a condition rather than a disease or a disorder by itself. However, babies born prematurely are at high risk of heart problems, breathing difficulties, jaundice, infections, and other health problems because their internal organs and immune systems are not yet fully developed at the time of birth.
Prematurity refers to birth before the thirty-seventh week of the mother's pregnancy. A premature or preterm baby is smaller than a full-term baby and weighs less. Premature babies (sometimes called “preemies”) need special care in the hospital after they are born and frequent medical checkups in the first two years after birth because of their increased risk of health problems. A baby may be born prematurely because of the mother's lifestyle or because of factors beyond the mother's control, including her age and basic bone structure.
Doctors describe babies born prematurely in terms of their birth weight as well as their gestational age (the number of weeks the mother was pregnant before the baby was born). Although birth weight usually increases along with gestational age, some babies are larger or smaller than normal for their gestational age. Preterm babies are classified according to their weight as follows:
- Low birth weight (LBW) babies are those that weigh less than 5 pounds 3 ounces (2,500 grams) at birth.
- Very low birth weight (VLBW) babies are those that weigh less than 3 pounds 5 ounces (1,500 grams) at birth.
- Extremely low birth weight (ELBW) babies are those that weigh less than 2 pounds 3 ounces (1,000 grams) at birth. About 10 percent of babies born with low birth weight are ELBW infants.
Because a higher gestational age makes a significant difference in a baby's chances for normal health and development as well as simple survival, the doctor will try to reduce the mother's risk of giving birth prematurely whenever possible. In some cases the mother may be advised to leave a job that requires long hours of standing on her feet, to eat a healthier diet, or to quit smoking. Another method that appears to be effective in reducing the risk of preterm delivery is injecting a hormone called progesterone or applying a cream containing the hormone inside the vagina.
About 12 percent of babies born in the United States—one out of every eight—are born prematurely. Prematurity is one of the leading causes of death among newborn babies; in the United States, it accounts for about 25 percent of deaths among newborns. There are about 500,000 babies born prematurely in the United States each year; 32,000 of these are ELBW infants.
Risk factors for low birth weight infants include:
- Low socioeconomic status
- African American race
- Mother's age below fourteen or over forty
- A history of giving birth to preterm infants
The cause of premature birth is not known in about 50 percent of cases. In the remaining half, the causes include:
- Mother's lifestyle. Drinking, smoking, using drugs, and not eating enough are factors in premature birth. Smoking alone is a factor in 15 percent of preterm births.
- Mother's age. Mothers younger than eighteen or older than thirty-five are more likely to have premature babies.
- Multiple pregnancy. Mothers who are carrying twins or triplets are more likely to deliver prematurely.
- Abnormalities of the mother's uterus.
- Diabetes or high blood pressure in the mother.
- Extremely overweight or underweight mother.
- Mother has had great difficulty getting pregnant.
- A history of miscarriages or abortions.
- Chronic infections of the vagina.
The signs that a mother is starting to give birth prematurely include contractions of the uterus that come more often than six per hour; a discharge of fluid from the vagina; diarrhea; spotting of blood from the vagina; a backache; or a feeling of pressure or pain below the abdomen.
Babies born prematurely are at risk for a number of severe health complications in later childhood as well as during infancy. These include:
- Breathing problems due to underdeveloped lungs
- Respiratory distress syndrome
- Heart problems
- Eye disorders
- Bleeding into the brain
- Developmental and learning disabilities
- Cerebral palsy
Doctors can estimate a woman's risk of giving birth prematurely by using a scoring system based on her age, medical history, daily habits, socioeconomic status, and the condition of her pregnancy. About 30 percent of women with high risk scores have their babies prematurely compared to 2 percent of those with low risk scores. One complication with estimating a baby's gestational age, however, is that many women are uncertain of the date of their last menstrual period.
To diagnose whether an expectant mother is about to give birth, the doctor will use ultrasound to measure the length and width of her cervix. This part of the uterus begins to dilate, or open up, as childbirth begins. It also becomes shorter. If the mother is having contractions, the doctor may time them as well as check to see whether the membranes surrounding the baby in the uterus have started to break.
After the baby is born, the doctor will check for health problems before the baby is placed in the newborn intensive care unit:
- Blood test. This is done to detect anemia and to evaluate the possibility that the baby will develop jaundice.
- Chest x ray. This is done to check the condition of the newborn's lungs.
- Spinal tap. This test may be done if the baby shows signs of an infection.
Treatment for prematurity may include trying to stop the birth process. There are several approaches that may be used. Depending on the mother's stage of pregnancy and how far the birth has progressed, bed rest may be enough to stop the contractions. Other approaches include giving the mother medications that stop the contractions or by putting stitches in the cervix (the neck of the uterus) to hold it closed until the last month of pregnancy, when the stitches are removed. Recent research indicates that giving progesterone, a female hormone, to pregnant women who have had a previous preterm baby reduces their risk of having their new baby born prematurely.
The specific treatments given to the baby depend on its weight at birth and its gestational age. As the care of premature newborns has improved since 1960, the lower limit of viability (the age at which 50 percent of premature infants will survive) has dropped from twenty-eight weeks to twenty-three to twenty-four weeks. The earliest premature baby known to survive is a Canadian boy who was born twenty-one weeks and five days after conception in 1987.
All premature babies are taken to a newborn intensive care unit or NICU. Care given usually includes:
- Being placed in an incubator or warmer. Preterm babies cannot regulate their own body temperature as well as full-term babies because they do not have as much body fat. VLBW babies have very thin skin in addition to little body fat.
- Surfactant. Surfactant is a substance secreted by cells in the lungs that keeps the lungs inflated when a person breathes in and prevents the lungs from collapsing when the person breathes out. Babies born before thirty-two weeks do not have enough surfactant in their lungs to breathe easily, so the doctor will administer some surfactant.
- Monitoring of breathing. Preterm babies often suffer from apnea, or temporary stopping of breathing, because the part of the brain that normally controls breathing is not fully mature. Infants who develop apnea can be put on a ventilator or in some cases given a medication to keep the airway open.
- Administration of fluids. Preterm babies lose more water through their skin than full-term babies, so fluids are administered intravenously to keep them from dehydrating.
- Special formula for nutrition. Preterm babies need to be fed intravenously for a few days after birth because their ability to suck directly from the breast or bottle is not fully developed. After the first few days, breast milk can be pumped from the mother and fed to the baby through a tube placed in the mouth that goes down into the stomach. Since a premature baby needs more calories than a full-term baby would in order to grow, extra fortifiers or vitamins and minerals may be added to the mother's milk.
The baby is considered well enough to go home from the NICU when it can breathe without a ventilator, is steadily gaining weight, can feed directly from the mother's breast or a bottle, and does not need to
be kept warm artificially. Children born prematurely, however, will need more frequent follow-up visits to the doctor than full-term babies. They are more vulnerable to infections, difficulties learning to speak and walk, and problems with vision and hearing. The doctor may recommend that the parents take the baby to a high-risk newborn clinic or early intervention program during its first two years of life.
The prognosis of premature infants depends on their age and weight at birth; the older the gestational age and the higher the birth weight, the better the baby's chances of survival. The three leading causes of death in premature infants are respiratory failure, infections, and birth defects. Advances in the care of premature infants in recent years have improved their chances of survival; more than 90 percent of babies who weigh 2 pounds (900 grams) or more at birth survive. ELBW infants have a 40–50 percent chance of survival but have a high risk of complications. Girls are more likely than boys to survive very early birth (twenty-two or twenty-three weeks).
WORDS TO KNOW
Apnea: Temporary stopping of breathing.
Cervix: The neck or lowermost part of a woman's uterus that opens into the vagina.
Gestational age: An infant's age at birth counting from the date of the mother's last menstrual period.
Jaundice: A yellowish discoloration of the skin and whites of the eyes caused by increased levels of bile pigments from the liver in the patient's blood.
Surfactant: A protein-containing substance secreted by cells in the lungs that helps to keep them properly inflated during breathing.
An expectant mother can reduce her risk of giving birth prematurely by getting regular prenatal care; eating a healthy diet; following the doctor's recommendations for chronic health conditions like diabetes and high blood pressure; avoiding tobacco, alcohol, and drugs; cutting back on work that requires standing on the feet; getting enough sleep; and managing stress.
Although weekly progesterone therapy is a relatively new preventive approach, women with several risk factors for preterm delivery or a history of giving birth prematurely may want to ask their doctor about it.
An important question that researchers are investigating is the reason for the rise in the number of premature births in the United States since 1981. In that year 9 percent of births were premature, compared to 12 percent in 2008—an increase of 31 percent. As there are no completely effective ways to prevent prematurity, an answer to this question might lead to better preventive approaches.
SEE ALSO Cerebral palsy; Congenital heart disease; Developmental disability; Diabetes; Hypertension
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