According to the World Health Organization (WHO), a preterm birth occurs when the child is born before the week 37 of pregnancy. Some of the most common causes of preterm birth are:
- Overdistention of the uterus: loss of tone in the uterine musculature that prevents this organ to recover its normal size.
- Infection or uterine inflammation: certain bacteria can damage fetal membranes by causing its rupture and triggering a preterm birth. An infection that affects the uterus directly may lead to preterm birth as well.
- Decidual bleeding: a type of vaginal bleeding that may occur while a woman is pregnant.
There exist many risk factors that can lead to premature birth, including obesity, high blood pressure, etc. A multiple pregnancy is one of these factors.