Chromosome abnormalities in the embryo or fetus. A chromosomal abnormality (usually an abnormal number of chromosomes) is the most common cause of pregnancy loss, and the risk increases with advancing maternal age. The most common abnormality that is diagnosed is trisomy (one extra chromosome). Chromosomal abnormalities can be confirmed by genetic testing of the pregnancy tissue after a pregnancy loss. Sometimes, parents carry chromosomal alterations called ‘translocations’ that do not affect them personally but can lead to pregnancy loss due to an abnormal chromosome number in the embryo. These can be investigated via a parental karyotype, a blood test that examines parental chromosomes.

Antiphospholipid antibody syndrome is a syndrome associated with both early and late pregnancy loss, as well as other pregnancy complications. It is recommended that patients with greater than 3 unexplained pregnancy losses before 10 weeks, or one pregnancy loss after 10 weeks with no genetic abnormality should undergo evaluation via a blood test.

Shape of uterus (bicornuate, unicornuate, septum) or presence of fibroids, polyps or scar tissue in the uterus. Anatomic causes are more commonly associated with second trimester loss. These can be investigated by 3D ultrasound, saline infusion sonogram, hysterosalpingogram (an X-ray of the uterus), or hysteroscopy (a small camera inserted into the uterus through the vagina).

Untreated medical conditions (e.g., thyroid disease, diabetes). Well controlled diabetes is not a risk factor for pregnancy loss, but poorly controlled diabetes and other hormonal abnormalities (high or low thyroid function, high prolactin levels) are associated with pregnancy loss.

A healthy lifestyle is recommended for anyone trying to conceive. Smoking tobacco, drinking alcohol (>3-5 drinks/week), and cocaine use have all been associated with an increased risk of miscarriage.