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What causes pregnancy loss/miscarriage?

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Miscarriage occurs due to many different causes, some of them known and others unknown. Frequently, miscarriages occur when a pregnancy is not developing normally. More than half of all miscarriages are caused by a chromosomal abnormality in the fetus (typically due to the wrong number of chromosomes, the structures in a cell that contain the genetic information), which is more common with increasing age of the parents, particularly among women who are older than age 35.1,2

Other possible causes of pregnancy loss or miscarriage are maternal health issues or exposure to chemicals. Maternal health issues include chronic disease, such as diabetes, thyroid disease, or polycystic ovary syndrome (PCOS), or problems associated with the immune system, such as an autoimmune disorder. Other maternal health issues that can increase the risk of miscarriage include infection, hormone problems, obesity, or problems of the placenta, cervix, or uterus.1 Exposure to environmental toxins, drug use3 or alcohol use4, smoking5, or the consumption of 200 milligrams or more of caffeine per day (equal to about one 12-ounce cup of coffee) also can increase the risk of miscarriage.6


  1. Branch, D. W., Gibson, M., & Silver, R. M. (2010). Clinical practice. recurrent miscarriage. The New England Journal of Medicine, 363(18), 1740-1747. doi:10.1056/NEJMcp1005330 [top]
  2. Nybo Andersen, A. M., Wohlfahrt, J., Christens, P., Olsen, J., & Melbye, M. (2000). Maternal age and fetal loss: Population based register linkage study. BMJ (Clinical Research Ed.), 320(7251), 1708-1712. [top]
  3. Keegan, J., Parva, M., Finnegan, M., Gerson, A., & Belden, M. (2010). Addiction in pregnancy. Journal of Addictive Diseases, 29(2), 175-191. doi:10.1080/10550881003684723 [top]
  4. Henriksen, T. B., Hjollund, N. H., Jensen, T. K., Bonde, J. P., Andersson, A. M., Kolstad, H., Ernst, E., Giwercman, A., Skakkebaek, N. E., & Olsen, J. (2004). Alcohol consumption at the time of conception and spontaneous abortion. American Journal of Epidemiology, 160(7), 661-667. doi:10.1093/aje/kwh259 [top]
  5. Mishra, G. D., Dobson, A. J., & Schofield, M. J. (2000). Cigarette smoking, menstrual symptoms and miscarriage among young women. Australian and New Zealand Journal of Public Health, 24(4), 413-420. [top]
  6. Weng, X., Odouli, R., & Li, D. K. (2008). Maternal caffeine consumption during pregnancy and the risk of miscarriage: A prospective cohort study.American Journal of Obstetrics and Gynecology, 198(3), 279.e1-279.e8. doi:10.1016/j.ajog.2007.10.803 [top]

Last Updated Date: 11/30/2012
Last Reviewed Date: 07/15/2013
Vision National Institutes of Health Home BOND National Institues of Health Home Home Storz Lab: Section on Environmental Gene Regulation Home Machner Lab: Unit on Microbial Pathogenesis Home Division of Intramural Population Health Research Home Bonifacino Lab: Section on Intracellular Protein Trafficking Home Lilly Lab: Section on Gamete Development Home Lippincott-Schwartz Lab: Section on Organelle Biology