Most miscarriages are a one time occurance, and occur due to chromosonal abnormalities occuring in the fetus. Up to 70% of all miscarriages occur due to chromosonal abnormalities occurring in a faulty egg or sperm. When and egg or sperm developes with with more or less than 23 chromosomes the resulting enbryo will have a chromosonal abnormality that will prevent it from developing properly.
Sometimes the chromosonal abnormaility will result in a blighted ovum, an instance where the placenta and the sac develop but contain no embryo. This is because the embryo failed to form at all during the pregnancy, or else stopped developing in the very early stages. A blighted ovum will result in a miscarriage, although it may take several weeks for the miscarriage to occur.
Other less common causes of miscarriage include:
- hormonal imbalances
- vaginal or uterine infections
- use of alcohol, drugs, or cigarettes
- weakened cervix
- abnormally shaped uterus
- immune system disorders
- clotting disorders of pregnancy
- exposure to harmful chemicals