Chromosomal Abnormalities as a Cause of Miscarriage

Question: What Causes Chromosomal Abnormalities That Lead to Miscarriage and Stillbirth?

Answer:

Of all miscarriage causes, chromosomal abnormalities are considered to be the most frequent explanation for why miscarriages happen. Estimates suggest that anywhere between 40 and 75% of all miscarriages can be explained by random genetic problems in the developing baby.

The question of what causes chromosomal abnormalities is a little more complex.

The simplest answer is that "it just happens." Cell division is a complex process with a lot of things that can go wrong, so it follows that sometimes things do go wrong. A sperm or egg cell may end up with the wrong number of chromosomes or with chromosomes with missing or extra pieces, which ultimately go on to cause problems such as miscarriage or stillbirth (or lead to genetic disorders).

Most of the time, women who have one pregnancy affected by chromosomal abnormalities will go on to have a normal pregnancy the following time -- so chromosomal issues are somewhat random in nature. Most of the time, chromosomal abnormalities do not recur unless one or both parents has a balanced translocation or similar genetic issue.

Parental age is one risk factor for having pregnancies affected by chromosomal abnormalities. In couples where the mother or father is older than 35, the risk of miscarriage grows and the frequency of chromosomal abnormalities appears to be higher.

For men, the age at which miscarriage rates increase is unclear, but is likely to be over 40 years old.

Researchers are investigating other risk factors for chromosomal abnormalities, but the data are not conclusive. For example, exposure to toxic chemicals (such as pesticides or bisphenol A -- a component in many plastic products) may increase risk of chromosomal abnormalities, but the exact relationship is not well understood.

With these theoretical risk factors, the research is not complete enough to draw definitive conclusions.

Sources:

Genuis, Stephen J. "Health issues and the environment—an emerging paradigm for providers of obstetrical and gynaecological health care." Human Reproduction June 2006 2201-08. Accessed 25 Nov 2007.

Hanke, W. and J. Jurewicz. "The risk of adverse reproductive and developmental disorders due to occupational pesticide exposure: an overview of current epidemiological evidence." International Journal of Occupational and Medical Environmental Health 2004 223-43. Accessed 25 Nov 2007.

Slama, Remy, Jean Bouyer, Gayle Windham, Laura Fenster, and Axel Werwatz and Shanna H. Swan. "Influence of Paternal Age on the Risk of Spontaneous Abortion." American Journal of Epidemiology 2005 816-23. Accessed 25 Nov 2007.

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