Almost anyone who has suffered a miscarriage or stillbirth worries about the risk of having subsequent losses. Recent information indicates that women should look into testing after two losses when it used to be common to wait until three. This is especially important for women in their 30s and 40s. Newer studies indicate a miscarriage rate of 26-40% after a woman has suffered two losses, so earlier testing makes sense both emotionally, physically, and in many cases financially as well.

The two major clinically important categories of causes for spontaneous abortion (miscarriage) are fetal and maternal.

Fetal causes include the genetic composition of the fetus.


Human live borns have a very low percentage of chromosomal abnormalities (about 0.6% or 1 in 170). This low percentage indicates that almost all chromosomal abnormalities are lethal and aborted early in pregnancy.

The only chromosomal abnormalities (other than those involving the X and Y sex chromosomes) that might result in a human live born are trisomy 21 (three of the 21 chromosome, known as “Down’s syndrome”), trisomy 18 (three of the 18 chromosome, known as “Edward’s syndrome” and all die during infancy) and trisomy 13 (three of the 13 chromosome, known as “Patau syndrome” and all die during infancy).

It often assumes that such losses are rare events when in fact they are common (but not commonly discussed)

Heavy smoking (uncommon for this to result in a loss)

Heavy smoking (uncommon for this to result in a loss)

Maternal causes include abnormalities in the “environment” in which the embryo and fetus develops. Known maternal causes related to an action of the mother are uncommon, but can include

Heavy smoking (uncommon for this to result in a loss)

Alcohol abuse (uncommon for this to result in a loss)

Irradiation or exposure to chemical toxins

Medications known to be teratogenic (cause fetal malformation)

Other maternal causes which are not related to any conscious activity of the mother or couple include


Anatomic abnormalities (typically uterine)

Hormonal imbalances (typically in progesterone)

Immunologic system errors (autoimmune and alloimmune)

Serious or life threatening maternal disease

By far the most common causes for spontaneous pregnancy loss are fetal not maternal. It is difficult for a woman with an undesired pregnancy to consciously create an unfavorable environment for the pregnancy to successfully force a miscarriage.

Often couples blame themselves for “doing something” that must have resulted in the pregnancy loss. Focusing on themselves (often harshly) for doing something wrong is unfortunate since


It adds guilt on top of an existing emotionally charged situation, which is counterproductive and may delay or arrest recovery from the event.

It is misdirected since very few losses are related to conscious maternal actions.

It often assumes that such losses are rare events when in fact they are common (but not commonly discussed)

An evaluation for known causes of recurrent pregnancy loss is usually initiated after 2 or 3 consecutive pregnancy losses. The tremendous emotional impact of each loss may encourage an evaluation sooner than later. A full evaluation includes


Demonstration of a normally shaped uterine cavity (by either hysterosalpingogram or hysteroscopy)

Tests to rule out infectious diseases

Evaluation for a hormonal deficiency in progesterone production (by either endometrial biopsy or bloodwork)

Analysis of both the maternal and paternal chromosomes (by bloodwork)

Laboratory testing for immunologic causes of pregnancy loss (by bloodwork)

Taking a history for maternal disease states, environmental or other toxin exposure

If a full evaluation is completed on couples with either 2 or 3 consecutive losses there will still be about 50% (1 of 2) of couples with “unexplained” recurrent pregnancy loss. That is, roughly half of couples seem to have a reason for recurrent loss that is beyond modern medicine’s ability to diagnose this cause. This can be frustrating for both the couple and the physician. In this situation, the couple will at least know that potentially repairable pathology has been ruled out.eo.