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KMID : 0377619960610040340
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Korean Jungang Medical Journal
1996 Volume.61 No. 4 p.340 ~ p.344
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Anticipating and Preventing Premature Labour
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Calder, Andrew A.
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Abstract
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Pre-term birth is the most important factor associated with perinatal morbidity and mortality. Even in developed countries with sophisticated neonatal intensive care services, pre-term birth is responsible for 50 to 70% of all deaths in the neonatal period (Villar et al, 1994) furthermore among babies who survive pre-term delivery the rate of morbidity is extremely high, with an increased risk of chronic lung disease, poor growth resulting in short stature, and re-admission to hospital after the neonatal period. Of even greater importance is the high rate of mental handicap and spasticity which may be a direct result of extreme prematurity.
Definition
Term has conventionally been defined as that period spanning the 38th to the 42nd week of amenorrhoea so that technically pre-term deliveries are those which take place before the 37th completed week of pregnancy. For practical purposes nowadays babies born between 34 and 37 weeks although technically pre-term, are not generally the source of serious anxiety, but as the length of gestation shortens so the incidence of death and disability increases. The definition of prematurity based on the period of amenorrhoea is of course subject to error as a result of inaccurate reporting of the menstrual data and the fact that even when the last episode of bleeding is accurately recorded, this may not bear a direct correlation with the time of ovulation and conception, as a result of the influence of factors such as irregularity of the menstrual cycle and the use of contraceptives. The increasing tendency to ultrasound scanning in early pregnancy has reduced the likelihood of error but because of these uncertainties some studies have concentrated on a definition based on the birth-weight of the infant. This however is even more subject to confounding variables such as influences which enhance or inhibit fetal growth in utero, not to mention the very large range of birth-weights of babies who are normally grown.
Classification of pre-term births.
As will shortly be discussed the aetiology of pre-term birth is highly complex and entails multiple factors. It is however appropriate to identify three large subgroups into which all pre-term births are likely to fall. Namely the beta adregernic drugs appear to be of little long term benefit although they may offer an opportunity to exhibit corticosteroids and improve the fetal lung maturity. The calcium channel blocking drugs appear to have similar efficacy to the beta adrenergic agents. It should also not be forgotten that these agents are potentially dangerous to the mother and instances of maternal death, particularly associated with beta mimetic agents figure prominently in the obstetric literature.
The family of "tocolytic" agents w rich are of undoubted efficacy are the prostaglandin synthesis inhibitors, notably indomethacin. Because of the known association between exposure of the fetus to indomethacin and premature closure of the ductus arteriosus there has been a reluctance to use these agents, nevertheless they remain the most potent and if used with care and appropriate monitoring of the fetal circulation and the amniotic fluid volume, they may prove to be of substantial benefit in the reduction of premature delivery among women who are at special risk. (Gamissans and Balasch 1993).
Conclusions
Pre-term delivery is a multifactorial phenomenon, and no single strategy will produce a significant impact on the overall incidence of this problem and the misery which it may inflict. Progress will only come from an organised approach which takes account of the wide range of causative and associated factors. The establishment of special antenatal clinics to study and manage women at increased risk would appear to offer the prospect of some significant if small improvement in this problem which remains perhaps the most important ongoing challenge in modern obstetrics.
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