Why Chromosomal Abnormalities Can Cause Miscarriage and Stillbirth

Chromosomal abnormalities are a common culprit in miscarriage and stillbirth. Given that many babies are born with genetic conditions such as Down syndrome and other trisomies, why is it that some chromosomal abnormalities lead to miscarriage?

Potential Causes of Miscarriage

Of all miscarriage causes, chromosomal abnormalities are considered to be the most frequent explanation for why miscarriages happen. Estimates suggest that anywhere between 50 and 70% of all miscarriages are caused by random genetic problems in the developing baby.

In most instances, scientists do not know the exact reason why chromosomal abnormalities lead to miscarriage. One theory is that the mother's immune system recognizes a problem in the developing baby's genes and thus ends the pregnancy. 

Another theory is that the developing baby ultimately reaches a point where the specific genetic problem causes the baby to stop growing. Certain genes might be missing that is necessary for continued development, or extra copies of certain genes might cause the baby or placenta to grow improperly.

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, stillbirth, or genetic disorders.

Risk Factors for Abnormalities

Most of the time, women who have one pregnancy affected by chromosomal abnormalities will go on to have a normal pregnancy since chromosomal issues are somewhat random in nature. Chromosomal abnormalities typically 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 is over the age of 35, the risk of miscarriage grows and the frequency of chromosomal abnormalities appears to be higher.

Researchers are investigating other risk factors for chromosomal abnormalities, but the data are not conclusive. For example, exposure to toxic chemicals may increase your risk of chromosomal abnormalities, but the exact relationship is not well understood.

If you are trying to get pregnant and have experienced two or more miscarriages in a row, get a referral to a fertility specialist or reproductive endocrinologist. Something other than a genetic fluke may be causing the recurrent miscarriages.

Further screening can help determine any underlying issues you or your partner may have. Your doctor may then recommend surgery, treating the underlying condition, lifestyle change, or fertility treatments (although many couples eventually conceive and carry a pregnancy to term without any intervention).