A pregnancy loss that occurs before six weeks of pregnancy, after a positive home pregnancy test or doctor’s pregnancy blood test but before ultrasound or histological verification, is defined as a “biochemical loss”. The clinical term “miscarriage” is used when ultrasound examination has confirmed that a pregnancy has existed. Miscarriages may be subdivided into early pregnancy losses (before gestational week 12) and late pregnancy losses (gestational weeks4 12 to 21). Three or more consecutive pregnancy losses before 22 weeks of gestation are considered recurrent miscarriages.
On average, early pregnancy loss occurs in an estimated 15% of conceptions, with significant variations among different age groups. The incidence of early pregnancy loss ranges from 10% in women aged 20–24 years, to 51% in women aged 40–44 years. Late pregnancy losses (12–22 weeks) occur less frequently and constitute around 4% of pregnancy outcomes.
The primary reason for early miscarriages is abnormalities in the embryo (75–85% of cases). For recurrent miscarriages, however, the incidence of embryo abnormalities is lower (29–60%). It is not known exactly what causes early miscarriages, but risk factors include: a malformation of the uterus, an immune rejection reaction, a tendency to develop blood clots, and thyroid dysfunction (including thyroid autoimmunity).
The male can also contribute to early pregnancy loss. Recent research has shown a significant link between sperm DNA quality and recurrent miscarriages. Males with DNA-damaged sperm accounted for 85% of the males in couples with recurrent miscarriages, versus 33% of the males in couples that conceive successfully.
Miscarriages can be due to formation of a blood clot in a blood vessel in the placenta (thrombosis). Both hereditary and acquired factors can be responsible for thrombosis, and one of the acquired factors is hyperhomocysteinemia—abnormally high levels of the amino acid homocysteine in the blood. In most cases, hyperhomocysteinemia is fairly easy to treat. It typically is due to deficiencies of vitamin B6, folic acid and vitamin B12, so supplementation can bring homocysteine levels back down into the normal range. (Fruitful for Her includes these important vitamins).
Thrombosis also can sometimes be treated with anti-coagulation therapy, such as low doses of heparin or aspirin. However, there is little clinical evidence showing that applying the treatment during pregnancy effectively increases the chance of live birth.