Cause of signs of miscarriage

During the first trimester, the most common cause of miscarriage is chromosomal abnormality – meaning that something is not correct with the baby’s chromosomes. Signs of miscarriage often include heavier bleeding and severe abdominal pain after tissues have expelled from the womb. An ultrasound usually reveals the remaining tissue.
The cause of a miscarriage cannot always be determined. The most common known causes of miscarriage in the first third of pregnancy (1st trimester) are chromosomal abnormalities, collagen vascular disease (such as lupus), diabetes, other hormonal problems, infection, and congenital (present at birth) abnormalities of the uterus.
Another cause of early miscarriage may be progesterone deficiency. Women diagnosed with low progesterone levels in the second half of their menstrual cycle (luteal phase) may be prescribed progesterone supplements, to be taken for the first trimester of pregnancy.