Sadly, miscarriages are a common occurrence, with one in six pregnancies ending before week 20. This is little consolation when you have lost a baby through miscarriage, and you may want to find out why it occurred and if you can reduce the risk of it happening again.
The vast majority of patients who have experienced a miscarriage will go on to achieve a healthy family, so its important to stay positive. However, a small percentage of couples will experience more than one consecutive miscarriage. If you have three or more consecutive early pregnancy losses this is called recurrent miscarriage, and affects about 2% of women trying to have a baby.
Some of the causes of miscarriage include:
- Random chromosome abnormalities
- Genetic abnormalities
- Parental chromosome abnormalities
- Uterine abnormalities
- Immune causes
- Blood clotting disorders
- Other medical conditions
- Hormone imbalances
Age is also an important factor. After a woman has turned 43, there is a 50% chance a pregnancy will spontaneously miscarry.
Don’t blame yourself for a miscarriage
Pathology tests are sometimes performed after a miscarriage, but usually, no cause can be identified. This can add to feelings of distress and disbelief, and may lead to feelings of guilt. However, doctors agree that a miscarriage is rarely caused by anything the mother did — or didn’t — do (for example, drank a glass of wine, ate a particular food, had sex or did not rest enough). In the majority of cases, the next pregnancy proceeds to full term.
The most valuable study to evaluate the reason why a miscarriage has occurred is chromosome analysis of the tissue which is miscarried. Obviously, this study can only be performed at the time of the miscarriage. If we can prove that the miscarriage resulted from a chromosome mishap, extensive blood studies and tests to look for alternative explanations may be avoided. Chromosome testing of the parents explains far fewer miscarriages than testing of the miscarried tissue.
Minor abnormalities in the way the uterus formed during fetal development may predispose a women to miscarry. Fibroid tumours and scar tissue within the uterus may also cause pregnancy loss. The uterus is evaluated by means of ultrasound or magnetic resonance imaging, direct visualization with a telescope (hysteroscopy) and /or a specialized x-ray known as hysterosalpinogram (HSG).
Two categories of immune system malfunction may result in miscarriage. First, the woman’s immune system may inappropriately attack pregnancy tissue. Blood tests may reveal misguided immune molecules such as anti-cardiolipin antibody or the lupus anticoagulant. Second, the immune system may fail to provide the normal protection usually provided to the pregnancy. These disorders are barely understood and not routinely studied.
A deficiency of the hormone progesterone will sometimes prevent successful implantation of a pregnancy into the inner wall of the uterus. Progesterone deficiency is detected by hormone determinations while pregnant or by blood testing and/or tissue biopsies in the non-pregnant state. When we detect a low progesterone level while a woman is pregnant, it is more likely the result of the pregnancy’s failure to develop and less likely to be the cause of the problem. Therefore, we need to be cautious about diagnosing progesterone deficiency as the cause of the miscarriage. Disorders of thyroid, prolactin and insulin may also be investigated with blood tests.
Infections within the uterus are commonly implicated as causes of pregnancy loss later on in pregnancy. Early losses (the subject of this discussion) are rarely attributed to infection. Sometimes women who have suffered several early losses will be checked for vaginal bacterial imbalance (BV) or ureaplasma infection.
Some women have inherited a genetic trait allowing their blood to clot too easily. The high estrogen levels of pregnancy may accentuate this tendency to clot, resulting in loss of blood flow to the pregnancy and resultant miscarriage. Many of these traits are able to be identified through blood tests.