Premature labor

Premature labor describes any onset of labor in a woman prior to the fetus reaching a gestational age of 37 weeks.  Although in most cases close to 37 weeks a fetus will be fully developed enough to survive outside the uterus, the lower the gestational age at labor, the less likely it is the newborn will be able to breathe withough outside intervention, usually with a gestational respirator, to maintain a constant body temperature of 98.5 F, or to take in nourishment.  Both birth mortality and infant mortality (death within the first year of life) are directly related to birth weight and gestational age at birth.
The causes of premature labor are poorly understood (as are the factors that set off labor in full-term mothers).  However, it is known that particularly in the United States, women are far more likely to enter premature labor than in most other industrialized countries and even some less developed countries.  Premature labor is a particular problem in mothers who have not had regular pre-natal care.  
In many cases, premature labor will continue to birth, but in extreme situations labor can be stopped for up to 72 hours by the administration of terbutaline.  In such cases, the mother will be given steroids to encourage development of the fetal lungs.