What causes complications in pregnancies?

Many reasons: Complications in pregnancy can be from the pregnancy itself, such as placenta problems, amniotic fluid problems and problems with the baby's development. Other reasons might be medical complications related to diabetes, high blood pressure, lupus and many other medical conditions. Other reasons can be self imposed such as smoking drinking and using drugs.

Lots of things: There are more complications in pregnancies than most people realize before they face them. Some are because of preexisting health issues in the mom. Some are just random chance birth defects. Some are conditions that run in families. Some don't develop until later, like gestational diabetes or hypertension. Is there a specific complication you are concerned about?