Which chromosomal abnormality constitutes the largest group among first-trimester spontaneous miscarriages with abnormal karyotypes?

• A Triploidy
• B Monosomy X (45,X)
• C Autosomal trisomy ✓
• D Balanced reciprocal translocation

Explanation

Roughly half of first-trimester abortuses have chromosomal anomalies, and autosomal trisomy is the largest category, accounting for about half of the abnormal karyotypes. Trisomy 16 is the single most frequently encountered trisomy in miscarried conceptuses and is essentially lethal in utero. Monosomy X is the next large group, but many 45,X embryos survive to term, making it the commonest anomaly among live-born girls rather than among abortuses. Triploidy and balanced translocations are far smaller categories.

Reference: Williams Obstetrics, 26th ed.

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