Population explosion

I'm in one of those weird phases where everyone everywhere seems to be having babies. I mean everyone. And this isn't just a product of the wave of everyone getting married, considering that (a) that was four years ago and (b) a lot of these are second babies, or babies late into marriages, things like that.

It started with the husband's friend's wife (the couple that had sworn they didn't want children) who had a little boy in early February. Next was a former coworker who had a little girl a few weeks ago. Another coworker is going out on leave next week in anticipation of the birth of her little girl. Then there's the wife of a friend from grad school and another woman at work.

Today, I even got an email with pictures of a newborn baby girl born to a couple that I didn't even know was expecting.

Why do these things come in waves? Do people sense each other's fertility? Is it contagious? If you miss one wave, are you destined to remain childless until the next one comes along?