Fertility is the capacity to conceive and carry a pregnancy, or to contribute sperm that can do that work. It is not a moral rating. It changes with age, health, timing, and luck. A person can be fertile and still not get pregnant in a given month. A person can be infertile and still have a full sexual life.

Egg numbers fall with time in a way sperm numbers usually do not. That asymmetry shapes a lot of clinic waiting rooms. Smoking, untreated STIs, and some cancer treatments cut odds on all sides.

Wanting sex and wanting a child can pull in opposite directions. Timed intercourse on ovulation days is efficient and can feel grim. Naming that grimness keeps it from turning into blame.

Contraception exists because fertility does. Treating fertility as always-on is how accidents happen. Treating it as a switch you can flip at forty without help is how grief happens.