Why Chromosomal Abnormalities Can Cause Miscarriage and Stillbirth

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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.

This phenomenon could explain why some certain types of chromosomal abnormalities lead to miscarriage while others do not. 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, 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.

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 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). 

7 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Hardy PJ, Hardy K. Chromosomal instability in first trimester miscarriage: a common cause of pregnancy loss?Transl Pediatr. 2018;7(3):211–218. doi:10.21037/tp.2018.03.02

  2. Hyde KJ, Schust DJ. Genetic considerations in recurrent pregnancy lossCold Spring Harb Perspect Med. 2015;5(3):a023119. doi:10.1101/cshperspect.a023119

  3. Ocak Z, Özlü T, Ozyurt O. Association of recurrent pregnancy loss with chromosomal abnormalities and hereditary thrombophiliasAfr Health Sci. 2013;13(2):447–452. doi:10.4314/ahs.v13i2.35

  4. Salmon JE. A noninflammatory pathway for pregnancy loss: innate immune activation?J Clin Invest. 2004;114(1):15–17. doi:10.1172/JCI22258

  5. Simpson JL & Carson SA. Genetic and Nongenetic Causes of Pregnancy Loss. The Global Library of Women's Medicine. doi:10.3843/GLOWM.10319

  6. Pourjafari B, Pour-Jafari H, Farimani M, Ghahramani S, Saleh EK. Genetic counseling in carriers of reciprocal translocations involving two autosomesIndian J Hum Genet. 2012;18(2):250–253. doi:10.4103/0971-6866.100802

  7. Kim H, Kwon HJ, Rhie J, et al. The relationship between spontaneous abortion and female workers in the semiconductor industryAnn Occup Environ Med. 2017;29:49. doi:10.1186/s40557-017-0204-x

Additional Reading
  • Genuis, Stephen J. Health Issues and the Environment—An Emerging Paradigm for Providers of Obstetrical and Gynecological Health Care. Human Reproduction June 2006 2201-08.

  • Hanke, W. and J. Jurewicz. The Risk of Adverse Reproductive and Developmental disorders Due to Occupational Pesticide Exposure: An Overview of the Current Epidemiological Evidence. International Journal of Occupational and Medical Environmental Health 2004 223-43.

  • 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.

By Krissi Danielsson
Krissi Danielsson, MD is a doctor of family medicine and an advocate for those who have experienced miscarriage.