Pregnancy is normally considered to last between 37 and 42 weeks from the first day of the last menstrual period. Premature babies are generally considered to be those born before 37 weeks. They are usually small, but they are at risk because of the immaturity of their organs and not solely as a result of their size. They are prone to low body temperature, prolonged neonatal, feeding problems and, most importantly, breathing difficulties. Because their lungs are immature, they may develop respiratory distress syndrome (RDS) or hyaline-membrane disease. The more premature the baby, the more likely he or she is to develop breathing difficulties. These difficulties are caused by the presence of a membrane in the lungs which prevents them from expanding and thus transferring oxygen properly. A baby with respiratory distress syndrome will usually have difficulty with breathing from birth, or within the first few hours. He or she usually has rapid, shallow breathing, draws in the muscles between the ribs and grunts during breathing. These babies can be treated with controlled amounts of oxygen given in incubators, either in the air in the incubator or more usually by means of tubes in the nose. This often gives very good results. Even if a baby has no breathing problems but is premature, he or she will probably be nursed in an incubator in a special baby unit at first, to provide the right environment and to allow the nursing staff and parents to monitor the baby’s condition easily and to enable the early detection of any problems.
‘Light-for-dates’ and dysmature babies
If a baby weighs less than the lower limit of the range considered normal for length of time spent in the womb, he or she is termed ‘light-for-date’ or dysmature. In most areas this lower limit is 2.5 kg after at least 37 weeks of pregnancy. A dysmature baby may be born at the expected time, and simply be small, or may be dysmature and premature. These babies are usually cared for at first in special babycare units, because they tend to gain weight poorly and are prone to low body temperature and low blood sugar (hypoglycaemia*). It is often difficult to know why babies are born lighter than normal, but factors such as maternal smoking and drinking to excess, and also poor placental function, can cause the problem.
As only four to five per cent of all pregnant women deliver exactly at the estimated date, it is obvious that almost half of the pregnancies last longer. In general this is not abnormal; it shows that birth is a natural phenomenon. If, however, a pregnancy lasts more
than two weeks beyond the estimated date the baby is called serotine or postmature. Of course pregnancy cannot last indefinitely. After a time the placenta is not able to perform its task any more, so in the end it is necessary to induce birth. Postmature babies are characterized by a dry peeling skin, without subcutaneous fat and without a fatty covering of vernix. Sometimes the baby has passed its first stool in utero, resulting in a yellow-green meconium*-staining of the skin and nails. With good care mostsoon recover and thrive well.
The most serious injuries which may happen to a baby during a difficult delivery are those to the brain. Bleeding, or haemorrhage, into the brain tissue is somewhat more likely to happen in a difficult breech delivery. Pre-term babies are also more prone to haemorrhages. This is why very small babies are often delivered by Caesarean section, which protects their heads. Babies have remarkable powers of recovery, and unless the bleeding is severe, most recover completely.
Cerebral palsy, a cause of spasticity, can result from bleeding into brain tissue, or by lack of oxygen (anoxia) during birth – for example, in a long and difficult delivery. Other injuries such as nerve damage from a breech delivery, or fractures, are uncommon but usually heal completely. The use of the vacuum extractor, or, instead of in some deliveries can cause slight damage to the scalp and an area of hair loss, but this is only temporary.