Causes of a Miscarriage

A miscarriage occurs if there is a sudden loss of a fetus before your 20th week of pregnancy. Miscarriages occur in about 15% to 25% of all pregnancies, but there are many different types of miscarriages and varying things that cause them to occur. Understanding what causes your miscarriage can help you and your doctor decide how to proceed when attempting to become pregnant again in the future.

Chromosomal Abnormalities

Up to 70% of miscarriages that occur in the first trimester are caused by a glitch in the genes of the fetus. There is no apparent reason for this random occurrence, sometimes the two sets of chromosomes from the egg and sperm simply don’t line up correctly during conception. Miscarriages that are a result of this type of abnormality do not signal any problems with the mother's or father’s fertility and will usually not affect your risk of miscarriage in the future.

Uterine Abnormalities and Incompetent Cervixes

Some women have a uterus that is abnormally shaped or divided, which can cause miscarriage, because the embryo cannot implant or can’t receive the necessary nourishment after implantation. This condition accounts for about 10% of miscarriages. An incompetent cervix is another problem that can lead to miscarriage. This means that the cervix is too weak to hold the fetus inside, causing the cervix to bulge. There are surgical procedures that can help correct these problems if your doctor discovers they are the cause your miscarriage.

Immunologic Disorders

In rare cases, the embryo is not accepted by the woman’s body and is viewed as a foreign object. This causes antiphospholipid antibodies to attack your own tissue, including the embryo, which will lead to a miscarriage. This condition accounts for many miscarriages that in the past were deemed unexplainable.

Untreated Illnesses

Untreated illnesses, such as thyroid problems and uncontrolled diabetes, will lead to unfavorable uterine environments. The effects of untreated conditions such as these will make it difficult for the embryo to survive inside the uterus, which will lead to a miscarriage. If you do have diabetes or thyroid problems, make sure you follow any recommended treatment regimens to keep these conditions under control and prevent further complications.

Polycystic Ovary Syndrome

PCOS is a condition that causes women to have elevated levels of male hormones, such as testosterone, which will lead to irregular ovulation and menstruation cycles. Because of this, the lining of the uterus is unable to mature properly, which can cause problems with fertility. There has been some success treating this condition with the antidiabetic drug, Glucophage (metformin).

Bacterial Infections

There are certain bacteria, such as mycoplasma hominis and ureaplasma urealyticum that live in the genital tracts of healthy women. However, if an infection of these bacteria occurs in a pregnant woman, this can greatly increase the chance of miscarriage. This is because these bacteria inflame the lining of the uterus and make it impossible for an embryo to develop. If the infection is detected, it can easily be treated with antibiotics. However, this can sometimes be difficult since it will usually not produce any symptoms.


Smoking, drinking alcohol, and using drugs can all contribute to your risk of having a miscarriage. Smokers have twice the rate of miscarriage as nonsmokers. Also, if you work in certain toxic environments, such as farms, operating rooms, dental offices, or hospital laboratories, you will have an increased rate of miscarriage as well.