Woman over thirty-five. If the father is over fifty-five, the risk of miscarriage is particularly significant, and thirty-five or not, particularly because of the risk of Down’s syndrome.

Paternal disorders
 Semen quality used to be thought of as a reason for a woman to miscarry. But now there seems to be evidence that a low sperm count has any significant effect. However, polyspermy—where too many sperm are in the seminal fluid (more than 250 million sperm in very milliliter of seminal fluid)—has been questioned as a cause of miscarriage. So far there is no strong evidence for this association.