The loss of a pregnancy is significant and not an uncommon occurrence. The thinking now is that a good portion of infertility is simply very early miscarriage. This theory was reported in the American College of Gynecology (ACOG) September 1995 Bulletin. "Approximately 50-70% of pregnancies end in spontaneous abortion. Most of these pregnancy losses are unrecognized because they occur before, or at the time of, the expected menses." When these patients are studied carefully, 15% show an unexpected pregnancy per menstrual cycle that didn’t take. The cause of miscarriage can be identified in most couples and treatment can often resolve the problem.

When Do Miscarriages Occur?

Most miscarriages occur within the first 12 weeks of pregnancy (first trimester). If vaginal bleeding occurs after a viable fetus has been documented, chance of miscarriage is increased to about 20 percent. The risk of miscarriage increases for women 35 years or older. One of the causes of early miscarriage is an abnormal number of chromosomes. In order to determine whether there is a genetic cause for miscarriage, a karyotype on the fetal tissue and/or on blood from both parents may be ordered. If both parents have a normal karyotype, it is likely that the miscarriage was a chance event and the couple should feel comfortable continuing to try to conceive.

Uterine Abnormalities

Approximately 10 to 15 percent of women with a history of recurrent miscarriage have an abnormally shaped uterus. A septate uterus, which involves tissue protruding into the inner cavity of the uterus, causes miscarriage due to inadequate blood supply to the fetus. 

Low Progesterone

In the luteal phase (second half of the menstrual cycle), under the influence of the hormone progesterone, the endometrium thickens and becomes a healthy environment for a growing embryo. If progesterone production is low, the endometrium fails, preventing the embryo from implanting. This is easily corrected by administering progesterone either by capsules, suppositories, or injection.


Infections may cause recurrent pregnancy loss. Chlamydia has been linked to miscarriages. Mycoplasma has also been implicated, but the evidence is not strong. Pregnancy loss and its relationship to the immune system is under investigation.

Another theory suggests that during a normal pregnancy, the fetus containing the male partner's foreign genes, survives in the female's uterus because of a protective response from the female's immune system. In certain couples, this protective response does not occur allowing the maternal immune system to actively attack the fetus, recognizing the male partner's material as foreign, resulting in miscarriage.

Smoking, Alcohol, and Drug Use

Smoking, drinking, and illegal drug use can increase the risk of miscarriage. Women should always consult their physician before taking any medicine during pregnancy, and they should also alert doctors and dentists before receiving x-rays or prescriptions for medicine.

Pregnancy After A Miscarriage

After a miscarriage, it's normal for patients to experience a period of grief. These reactions are normal, and it is important to understand that each patient may feel and cope differently. Although it may be difficult, patients should talk about the loss with family and friends.

Some women who have experienced recurrent miscarriage may feel doubtful that they will ever have a child, but the encouraging news is that the success rate with treatment is high, especially with certain uterine and hormonal causes. In cases where no cause is discovered and no treatment prescribed, the chance of achieving a healthy pregnancy despite having had several miscarriages is still generally better than 50 percent.