Premature birth

DEFINITION: Premature birth is childbirth occurring before the thirty-seventh week of pregnancy; premature infants are those babies born before this time.

Babies born later than the thirty-seventh week of pregnancy and before the forty-second week are known as term or full-term infants, and birth anywhere during this period is within the window of normal gestation. By definition, babies born at or before the thirty-seventh week are called preterm or premature infants. (Babies born beyond the forty-second week are post-term infants.)

Every pregnancy and birth carry risk to both infant and mother. Preterm and premature infants, however, are at high risk. They have both a lower survival rate and more medical complications with potential lifelong effects than full-term babies. The World Health Organization estimated that in 2020, a little over thirteen million babies were born prematurely. Preterm infants make up the majority of the low-weight births that occur annually and a large proportion of infant deaths.

Developmental prematurity and survivability. Prior to twenty-four weeks of gestation, fetuses are not considered to have developed sufficiently to live outside the womb. Somewhere between twenty-four and twenty-eight weeks of gestation, however, the fetus does become viable, although any baby born between twenty-four and thirty weeks is called very premature. The lengths of these infants range from eleven to eighteen inches, and weights can range from one pound, five ounces to almost four pounds. At this stage of development, a few ounces more or less make a big difference in the baby’s ability to survive. Neonates at two pounds have little better than a one in two chance of survival; infants at 3.5 pounds have better than a nine in ten chance.

Babies born between thirty-one and thirty-six weeks of gestation are considered moderately premature. These babies do well, with a 90 to 98 percent survival rate, and weigh from a little more than three to almost four and one-half pounds. Typical lengths range from sixteen to nineteen inches.

Very premature babies still appear much less like babies, are significantly lighter, and remain behind developmentally. They are often unready to be bottle-fed or breast-fed or to sleep in an open crib, and they are generally less alert and have less behavioral control than the moderately premature. Simply reaching the same number of chronological weeks as moderately premature babies does not negate the substantial differences in their developmental beginnings.

Borderline premature infants born during weeks thirty-seven or thirty-eight are much like full-term newborns: They have almost the identical survival rate (98 percent) and approach average weights. Nevertheless, they are still at greater risk for respiratory distress syndromes, neonatal jaundice, unstable body temperatures, and a variety of problems associated with feeding. Cerebral palsy, impairment or loss of vision or hearing, and developmental delays are other potential problems facing premature babies.

The causes of prematurity and preterm births. Although many conditions result in premature birth, not all causes are known. Some well-known causes include toxemia in the mother (a multistage disease that begins with high blood pressure and rapid fluid retention and may progress to brain hemorrhage, seizure, and coma), placenta previa (when the placenta implants in the lower uterus), placenta abruptio (when a normally positioned placenta detaches from the uterus), premature membrane rupture (when the tissue containing the amniotic fluid tears or leaks before labor begins), incompetent cervix (when the cervix opens mid-pregnancy), and multiple births (twins, triplets, and so on). Cigarette smoking, alcohol use, drug use, or high stress levels during pregnancy also increase the risk of premature birth. High or low maternal age, hypertension, diabetes mellitus, sickle cell disease, kidney disease, lower socioeconomic status, and African American race are other risk factors for premature birth. For pregnant mothers who have had multiple previous preterm births or late-term miscarriages due to a short or an incompetent cervix, a procedure called cervical cerclage, in which the cervix is stitched shut until the thirty-seventh week, may be recommended.

Some mothers blame themselves for the premature births of their infants. While it is natural to look for a cause and a target to vent the often-powerful feelings associated with prematurity, it is the rare mother who deliberately causes her baby to be born earlier than necessary. In fact, some causes do not involve the mothers at all, including congenital defects in the infant, intrauterine illnesses, and defective placentas.

The majority of mothers will never deliver prematurely. Those who do, however, run a significantly higher chance of having a future premature birth. In the rush to understand and find answers to prematurity, it is important not to overinvest in probability statistics and comparative risk factor data, which include race, paternity, and even one's own mother’s exposure to biochemicals. It is extremely important to realize that many who are formally classified as high-risk mothers have normal deliveries of full-term babies, and that others, who are healthy and without known risk factors, deliver premature, preterm babies.

In 2003, scientists announced an exciting discovery in the search for preventing premature labor and birth. More than three hundred high-risk pregnant women—those who had given birth prematurely before—were given weekly injections of the hormone progesterone. This therapy reduced the chance of preterm birth by 34 percent, a number that elated the study’s researchers. The use of progesterone therapy has been especially effective in the cases of women with short cervixes. Another study in 2002 suggested that measures used to detect early labor—including a medical device worn on the abdomen to record contractions, ultrasound examinations of the cervix, and a test for a chemical called fetal fibronectin—seem not to work very well in preventing preterm birth, leading researchers to continue to seek ways to predict and prevent premature delivery. Early detection of labor is important because it can allow doctors to prescribe antibiotics, medication to slow the contractions or help the fetus develop more quickly, or bed rest.

In the early 2020s, experimental artificial intelligence and machine learning models were tested for predicting preterm birth. Using electrohysterogram measurements and clinical data, scientists believed they could better predict an early delivery, but the use of such technology remained rare in the early 2020s.

Warning signs of premature labor include a contraction every ten minutes within one hour before thirty-seven weeks of pregnancy, menstrual-like cramps, pelvic pressure, and an increase in vaginal discharge. If someone who is pregnant suspects they are going into labor prematurely, they should call their health-care provider immediately and continue to monitor their symptoms. Sometimes, lying down and hydrating can cause preterm contractions to abate; however, if the symptoms of premature labor continue, the pregnant person should seek immediate medical attention. Tocolytic medications such as intravenous magnesium sulfate may be given to slow preterm contractions, and corticosteroids may be administered to accelerate the baby's lung and brain development prior to preterm delivery.

More rarely, a premature birth will be performed intentionally by a medical professional when a potentially life-threatening condition arises, such as preeclampsia. Also, some choose to induce labor at thirty-seven or thirty-eight weeks; however, most medical authorities recommend waiting until at least thirty-nine weeks because of the benefits to the infant from longer gestation.

The psychological impact. There may be no event with a greater impact on a person’s life than becoming a parent, and few events in a parent’s life equal the impact of seeing one’s tiny, struggling, and high-risk baby. It is common for parents to have been forewarned of the baby’s chances, especially if the infant is very premature. They may, in fact, have begun to prepare themselves psychologically for the death of their baby even as the baby clings to life outside the womb. They may try to protect themselves from bonding to one whose death may be imminent.

Their distress, confusion, and contradictory feelings can overwhelm them. Their babies may not look much like the babies they had pictured or prepared for, and they may not feel much like parents. Premature birth can be a crisis rarely equaled in a parent’s life.

Some couples react and adapt successfully, while others do not. Nearly all parents of premature infants experience various forms of shock, denial, anger, guilt, and depression. Researchers who study and compare parents who cope better and worse have learned that those parents who accept and express their whole range of emotions (versus only the emotions that they believe they are supposed to have), seek further information, accept help in their caring for the babies, and begin to develop an early relationship with their babies adapt to the crisis well and successfully.

Premature infants were once thought to be inactive, unaware, and inert. Research and anecdotal observation strongly support the view that these infants are acutely sensitive to their environment, though they respond in ways too subtle to be perceived casually. When parents are present, even on the outside of the incubator wall, their babies behave differently, tolerate feedings better, and heal more quickly and completely.

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