(Updated to add proper attribution.)
A pregnant woman’s immune system, which normally treats any unfamiliar cells as a potential threat to be attacked with overwhelming force, has to know not to attack the fetus inside her body. Many scientists are studying the process the immune system uses to make this distinction, especially since, as this Nature article points out, failure of the system may be one cause of infertility.
In 1989, a young British woman had her ninth consecutive miscarriage. Her marriage broke down shortly afterwards. But within months of finding a new partner, she had conceived again and the pregnancy went without a hitch. Her daughter is now a healthy and lively nine-year-old.
Reproductive immunologists suspect that the woman’s immune system took offence at her first choice of partner — over-reacting to tissues carrying his genes and expelling the fetuses he fathered.
My wife, who pointed this article out to me, observed that this (1) puts an interesting spin on the Talmudic rule (which is hardly ever enforced, even in black-hat communities) that if a couple has been married for ten years and not had a child, they should get divorced; (2) may explain why her allergies went away while she was pregnant.