| Preterm birth remains a major cause of newborn and | | | | apart, can measure the fetus's rate of growth. Proper |
| infant illness and death. If its causes were better | | | | growth may also be determined by using a variety of |
| understood and prevention or treatment more | | | | ultrasound measurements to assess the relationship of |
| effective, fewer babies would die every year. For a | | | | the size of the head, for example, to the size of the |
| pregnant woman, prevention of preterm birth requires | | | | abdomen. If there is a big discrepancy between these |
| knowing the early signs of impending labor and seeking | | | | two, the baby may be growing improperly. |
| prompt care should any occur. | | | | Although 37 weeks gestation is considered mature, a |
| There is no exact physical or physiologic point at which | | | | fetus can reach maturity as early as 35 weeks. This |
| a fetus ceases to be premature and becomes | | | | does not mean that younger or smaller babies cannot |
| mature, no matter how precisely the pregnancy is | | | | survive. Today, they frequently do. With neonatal |
| dated. All the changes that occur are gradual, | | | | intensive care, highly sophisticated equipment for |
| especially in the latter two-thirds of the third trimester. | | | | assisting babies to breathe, a recently developed |
| There are no great leaps forward in baby behavior | | | | medication called surfactant, which helps the lungs stay |
| from one day to the next. In general, however, 37 | | | | expanded, and round-the-clock attention by expert |
| weeks completed gestation is considered mature. Any | | | | staff, premature babies have a better chance of |
| labor occurring before 37 weeks is considered | | | | survival than they did a few decades ago. Newborns |
| preterm labor and any baby born before 37 weeks is | | | | can survive with birth weights as low as 500 |
| considered preterm. | | | | grams(just over one pound) and a gestational age of |
| Today, a distinction is made between premature | | | | about 23 or 24 weeks. Such tiny infants, however, |
| babies and preterm babies. "Maturity" refers to how | | | | often have developmental problems in childhood. |
| well the baby is able to function outside the womb, | | | | Most of the difficulty in functioning among preterm |
| with the most emphasis on the respiratory system, as | | | | babies is seen in babies less than 34 weeks |
| breathing is a crucial function the baby must assume. | | | | gestational age. Government statistics today make a |
| A baby whose lungs cannot function is "premature." A | | | | distinction between moderately preterm births(32 to 36 |
| "preterm" baby is one whose gestational age is less | | | | weeks) and very preterm births(less than 32 weeks |
| than 37 completed weeks gestation. Some "preterm" | | | | completed gestation). Distinctions are also made |
| babies may not be "premature" from the perspective | | | | among low birth weight(less than 2,500 grams or |
| of their ability to breathe. | | | | 5½ pounds), very low birth weight(1,500 grams or |
| Acknowledging the difficulty in precisely dating a | | | | less, approximately 31/3; pounds), and extremely low |
| pregnancy, particularly prior to ultrasound, experts in the | | | | birth weight(1,000 grams or less, approximately |
| early part of the twentieth century suggested defining | | | | 2¼ pounds). |
| prematurity by weight, not gestational age. Any baby | | | | In 1998, the overall percentage of premature births in |
| weighing less than 2,500 grams (2.5 kilograms), or | | | | the U.S. was 11.6. This rate has been on the rise. In |
| approximately 5½ pounds, was considered | | | | 1990, it was 10.6 percent; in 1981, 9.4 percent. Most of |
| premature. However, using weight imposes its own | | | | the increase in 1998 was in the moderately preterm |
| imprecision, as weight varies greatly with many other | | | | group-babies born between 32 and 36 weeks |
| factors. We now make a distinction between birth | | | | gestation. |
| weight and gestational age. | | | | One major reason that preterm births are rising is that |
| A baby's birth weight may be said to be appropriate | | | | multiple births have become more common. |
| for gestational age(AGA) or small for gestational | | | | Pregnancies with more than one baby are more likely |
| age(SGA). Small babies may be small because they | | | | to end prematurely than are pregnancies with only one |
| are preterm or small because they are "growth | | | | baby(called singleton pregnancies). Multiple birth babies |
| retarded," or "growth restricted." A baby may be both | | | | are also more likely to be low birth weight. |
| preterm and small for gestational age. | | | | Two trends account for the recent increase in multiple |
| If two babies are the same birth weight, but one is | | | | births. One is the greater number of births to women in |
| born at 33 weeks and is the appropriate weight for | | | | their thirties, who are naturally more likely to have a |
| this gestational age and the other is a growth | | | | multiple birth than younger women. The other is the |
| restricted baby born at 38 weeks, in general, the older | | | | proliferation of fertility treatments, some of which result |
| infant will have an easier time adapting to life outside | | | | in multiple fetuses. About 80 percent of births of triplets |
| the uterus. If a baby is large, but born early, it may still | | | | or more were due to fertility treatment in 1996 and |
| have the problems that accompany early birth. The | | | | 1997. In 2000, 18 percent of births to women aged 45 |
| baby who will have the most trouble is the one who is | | | | to 49 years was a twin, triplet, or higher order multiple |
| both premature and small for gestational age. | | | | birth. In 1999, one out of every 3 births to women aged |
| Prior to delivery, when the baby can physically be | | | | 50 or older was a twin or triplet or higher-order multiple |
| examined to determine its gestational age, the date of | | | | birth. |
| the first day of the last menstrual period is the best | | | | We cannot discuss the rate of prematurity in the |
| single piece of information regarding the duration of the | | | | United States without noting the difference between |
| pregnancy. When a woman does not remember this | | | | the rate for Caucasian women(10.2 percent) and for |
| date, when she has irregular periods or gets pregnant | | | | African-American women(17.6 percent). A small part |
| after discontinuing a birth control method that made | | | | of this difference is due to the slightly more common |
| her periods stop, such as Depo-Provera(the "shot"), an | | | | occurrence of multiple births among African-American |
| ultrasound determines the duration of pregnancy. | | | | women. Socioeconomic background (poverty, |
| Ultrasound may also be relied upon when the uterine | | | | inadequate nutrition, and lack of access to health care) |
| size does not match the dates. The ultrasound may | | | | accounts for another part of the difference. Even |
| need to be repeated to ascertain if the difference in | | | | among African-Americans who have achieved a high |
| uterine size and menstrual dates(called a size-dates | | | | socioeconomic status, however, there is a difference in |
| discrepancy) is due to the baby growing excessively | | | | the preterm birth rates compared with Caucasians. |
| or not growing adequately, or if in fact the baby is | | | | We can only reflect that racial inequalities in this |
| growing as expected, just older or younger than the | | | | country continue to have effects even when aspects |
| dates suggest. Serial ultrasounds, done several weeks | | | | of inequity are overcome. |