What are the common genetic causes of recurrent miscarriage?

Embryonic aneuploidy is the most common cause. ASRM (2026): approximately 50–60% of first-trimester miscarriages are due to embryonic aneuploidy. The rate correlates strongly with maternal age — around 50% of tested miscarriages in women under 35, and 75% in women over 40. A point that reframes counselling: compared with individuals having isolated miscarriage, patients with RPL have a HIGHER likelihood of euploid miscarriage, and that likelihood increases further with the number of miscarriages. So while aneuploidy dominates overall, recurrent loss selects for the euploid — which is precisely why chromosome testing of the miscarriage is informative rather than merely confirmatory. Aneuploidy plays a smaller role later: 20% of stillborn fetuses at 22 weeks, 6% of stillborn infants at term, and 0.1–5% of term live births. Parental balanced structural rearrangements account for a small proportion and are the indication for parental karyotyping — see the dedicated question. On testing platform: no single technique detects all abnormalities. Conventional karyotype detects mosaicism and balanced rearrangements. SNP microarrays give uniparental disomy and consanguinity information, rule out maternal cell contamination, and identify parent of origin. Array CGH cannot detect balanced translocations; SNP cannot detect balanced tetraploidy. NGS detects segmental aneuploidy and mosaicism. On PGT-A: ASRM states it has not been shown to significantly reduce miscarriage or improve live births versus expectant management in RPL. In women over 40 with a proven aneuploid miscarriage it is reasonable to discuss using shared decision-making — with counselling that it has not been shown to reduce time to pregnancy or increase live birth rate.