The birth process can be separated into three principle phases: the beginning of contractions, the softening of the cervix and the rupture of the fetal membranes.
In pathological situations, one or more of these steps can be perturbed. Although we have a great deal of experimental information about the events which occur, we know virtually nothing about what initiates these events in humans. Despite decades of research, scientists have not yet developed effective ways to help prevent premature delivery. In fact, according to the March of Dimes Foundation, the rate of premature birth increased almost 35 percent between 1981 and 2005 (9.4 to 12.7 percent).
Certain risk factors are known which predispose to preterm labor, but these account for maximally 50% of all cases and include:
Smoking, alcohol and drug abuse, domestic violence (including physical, sexual or emotional abuse), infections (urinary, vaginal, sexually transmitted; possibly others), diabetes, high blood pressure and obesity.