Up to 20 percent of all detected pregnancies miscarry before week 20 of gestation. A miscarriage may also be referred to as a spontaneous abortion or a missed abortion. Approximately half of all miscarriages are caused by chromosomal or genetic abnormalities, while in the other half the cause remains unclear.

Other factors to be considered in a miscarriage are:

• Hormonal deficiencies

• Abnormalities of the cervix or uterus

• Incompatible blood types or the Rh factor

• Viruses and infections

• Immune disorders