Just as the premature baby requires special consideration, so too does the baby whose birth comes later than the statistically normal time for delivery. We define postmaturity as a gestational age at birth of greater than forty-two weeks. (The gestational age of the full-term baby, you will recall, is between thirty-eight and forty-two weeks, and the pre• mature’s is under thirty-eight weeks.) Though much investigative work has been done and is being done on the initiation of labor, medicine is still in the dark about the cause (or causes) of postmaturity. For that matter, we do not understand with
any great precision why it is that most women should go into labor between thirty-eight and forty-two weeks after conception, or why some women should deliver weeks earlier.
The primary importance of these investigations lies, of course, in the implications for the newborn who has arrived ahead of his time or after. Except for their unusually wide-eyed alertness, the great majority of postmature babies cannot be distinguished from their full-term fellows. A small minority of them do show some signs of malnutrition These are referred to as dysmature postmature infants.
Their physical condition gives every indication of their having lost some weight from a high point in the womb. The skin has a sagging looseness that is characteristic of adults who have been on a crash diet; it must previously have enveloped an accumulation of fat. The characteristically fine hair of the full-term infant (the lanugo) is missing. The skin tends to be cracked and dry, parchment like, and within hours it may begin to peel, particularly on the hands and feet. The fatty vernix caseosa (see page 257) we expect to find covering the full-term infant is usually absent. The fingernails are long enough to need trimming at once.
The nails, skin, and umbilical cord may all show yellowish green staining from meconium evacuated into the amniotic fluid prior to delivery. The dysmatures may have some problems in establishing normal respiration, in maintaining normal levels of blood sugar, and in nervous function, but these problems are in general manageable. The baby too impaired by malnutrition to sustain life is rare in this very small percentage of all postmates. The explanation for the malnutrition in dysmature postmaturity probably is to be found in malfunction of the placenta.
The amounts of oxygen and nutrients available for proper metabolism must decrease as the placental functioning slows or fails altogether. It is to be hoped that current research in these related fields of investigation will soon provide answers.
PROBLEMS OF PREMATURITY
There are all degrees of prematurity, from mild to severe. The more immature the baby the greater the risk of early death. At a certain point, prematurity blends with miscarriage: the fetus is not sufficiently developed to survive.
On the scale of birth weight we can give a rough idea of the expectations. A baby weighing between five and five and one. half pounds at birth has a better than nine to one chance of surviving, whereas only about 3o percent of the babies under three pounds will survive. But we repeat with emphasis that birth weight alone is prob-ably not as important as the maturity of development.
On the basis of gestational age (an indication of maturity) thirty-three weeks seems to be an important dividing line in terms of mortality. Nevertheless, the rule holds: the smaller and less mature the baby, the greater the risk of death, the higher the rate of complications, and the longer the stay in hospital under observation. Of course, there are prematures and pre-matures. To some babies premature birth seems to make no difference at all. For others it makes all the difference in the world. This variation from individual to individual has to be kept in mind in any discussion of the care of these early infants.
Compared to full.term babies. prematures are much more sensitive to the medications that are given in labor. As you have read elsewhere . these drugs are transferred from the mother’s blood to the baby’s through the placenta. Depression of nervous function, resulting in sleepiness, slowed respiration. and other physiological changes, is a side effect of pain-killers. Premedication of labor can depress all babies. Aware of this problem, obstetricians are more stingy now than they used to be in the amounts of pain•relieving drugs they give for childbirth.