I had this problem a lot before I had my first (only thus far) daughter. The true answer was tht I was desperately trying to get pregnant and was having monthly weeping sessions over negative pregnancy tests for a couple of years. But that was information I wanted to share or be forced to think about at work, on the bus, in the supermarket, at parties. Sometimes I felt like saying ‘well yes my husband and I are having a lot of unprotected sex, since you asked!’ because really, questions like that are fundamentally allusions to sex which is perhaps another reason why women get them more than men do. A male boss is far less likely to feel entitled to ask such things of a male employee.
I still get the questions now about ‘number two’ but have more emotional fortitude to answer them now. Still… when it’s virtual strangers, it bugs me.