Once an older woman does become pregnant, she runs a greater risk of miscarriage, foetal and chromosomal abnormalities, and pregnancy-related diseases.

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The biological reasons for why this may be are unclear, but the researchers speculated that potential chromosomal abnormalities in the eggs of older women and mutations in the sperm of older men may be a factor.

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Egg abnormalities also usually involve larger chromosomal changes, and are therefore easier to test for.

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