What Causes Miscarriage?

Miscarriage is far more common than people realize, and hardly ever discussed. If you have experienced one, you may be left wondering why it happened. This guide covers what research tells us about miscarriage, what typically doesn't cause it, and where genetics fits in.

How common is miscarriage?

Over 1 in 10 known pregnancies end in early pregnancy loss.¹ If you've experienced a miscarriage, you are far from alone.

What typically doesn't cause miscarriage

Many people blame themselves after a loss. According to the American College of Obstetricians and Gynecologists, the following typically do not cause miscarriage:¹

• Exercising²
• Having sex³
• Past birth control pill use⁴

Every situation is unique, and this guide does not replace what your own doctor knows about your health. When in doubt, talk to your doctor about yours.

The most common cause: chromosome differences

About half of first-trimester miscarriages are associated with a chromosomal difference in the embryo, such as a missing or extra chromosome.⁵ These changes usually happen by chance as the embryo forms; there is nothing someone did to cause it. The one large contributing factor that does raise the odds of a chromosomal difference is age: the chance increases as the age of the egg (and the person carrying the pregnancy) goes up.⁶

Other known contributors

Chromosomal differences don't explain every loss. Other well-documented contributors include:⁷

• Uterine structural differences (e.g., septum, fibroids, polyps)
• Endocrine factors (e.g., thyroid disease, diabetes)
• Antiphospholipid syndrome and other immune factors
• Chronic endometritis and other infection-related factors

In many cases, no clear cause is identified, even after a complete diagnostic workup.

Where single genes fit in

Even a pregnancy with an expected number of chromosomes can fail to implant, or be lost, sometimes for reasons we still don't fully understand. Separate from chromosome number, researchers have also identified specific single-gene changes that can:

• Affect implantation, making it harder for an otherwise chromosomally typical embryo to implant⁸
• Disrupt development, interfering with normal embryo development in ways that can lead to miscarriage⁹
• Cause severe genetic syndromes, severe enough that a continuing pregnancy could likely lead to stillbirth or early neonatal death⁸

For families going through IVF, Orchid's failed implantation, miscarriage, and stillbirth panel screens embryos for 130+ genes in addition to chromosome differences. Each gene is supported by published evidence linking it to these severe outcomes. This helps you and your care team prioritize embryos for transfer. This is an active area of research, and the screening will continue to improve over time.

A few things to keep in mind

• No test can guarantee a healthy baby. Many factors that contribute to failed implantation and miscarriage, genetic and non-genetic, are still unknown to science.
• PGT is a screening test, not a diagnostic one. It doesn't replace care recommended during pregnancy, including ultrasound and diagnostic testing such as amniocentesis.
• This is one part of a larger picture. Your care team and genetic counselors are your best resource for understanding what your results mean for you.

Questions? Orchid's genetic counselors are happy to help. Email genetics@orchidhealth.com.

This material is for general educational purposes and is not a substitute for medical advice, genetic counseling, or diagnostic testing.

References

1. American College of Obstetricians and Gynecologists. Early Pregnancy Loss. acog.org/womens-health/faqs/early-pregnancy-loss
2. Barakat, R., Zhang, D., Silva-José, C., Sánchez-Polán, M., Franco, E., & Mottola, M. F. (2023). The influence of physical activity during pregnancy on miscarriage—Systematic review and meta-analysis. Journal of Clinical Medicine, 12(16), 5393. https://doi.org/10.3390/jcm12165393
3. Niles, K. M. (2022). Sex in the first trimester. In D. Farine & P. T. González (Eds.), Sex and pregnancy: From evidence-based medicine to Dr Google (pp. 70–76). Cambridge University Press.
4. Yland, J. J., Wesselink, A. K., Hernandez-Diaz, S., Huybrechts, K., Hatch, E. E., Wang, T. R., Savitz, D., Kuohung, W., Rothman, K. J., & Wise, L. A. (2023). Preconception contraceptive use and miscarriage: prospective cohort study. BMJ Medicine, 2(1), e000569. https://doi.org/10.1136/bmjmed-2023-000569
5. Pylyp, L. Y., et al. (2018). Chromosomal abnormalities in products of conception of first-trimester miscarriages detected by conventional cytogenetic analysis. Journal of Assisted Reproduction and Genetics, 35(2), 265–271. PMID: 29086320
6. Elmerdahl Frederiksen, L., Ølgaard, S. M., Roos, L., Petersen, O. B., Rode, L., Hartwig, T., Ekelund, C. K., Danish Central Cytogenetics Registry Study Group, & Vogel, I. (2024). Maternal age and the risk of fetal aneuploidy: A nationwide cohort study of more than 500 000 singleton pregnancies in Denmark from 2008 to 2017. Acta Obstetricia et Gynecologica Scandinavica, 103(2), 351–359. https://doi.org/10.1111/aogs.14713
7. Practice Committee of the American Society for Reproductive Medicine. (2026). Recurrent pregnancy loss: a committee opinion. Fertility and Sterility, 125(6), 1023–1041. https://doi.org/10.1016/j.fertnstert.2026.03.001
8. Hyde, K. J., & Schust, D. J. (2015). Genetic considerations in recurrent pregnancy loss. Cold Spring Harbor Perspectives in Medicine, 5(3), a023119. PMID: 25659378
9. Quintero-Ronderos, P., et al. (2019). Potential genetic causes of miscarriage in euploid pregnancies: A systematic review. Human Reproduction Update, 25(4), 415–428. https://doi.org/10.1093/humupd/dmz015