CHICAGO -- Gene Hall gave birth Thursday morning to her third daughter, Kayla -- a baby that, when you do the math, was conceived in the aftermath of February's colossal blizzard."We were stuck in the house that week because of the snow, my husband and I and our kids, all homebound, playing games and watching movies," Hall, 32, of Chicago's Chatham neighborhood, said before the delivery. "When I look back now, I remember my husband and I got some good quality time together."We thought we were done having children. This snowstorm baby was a blessed surprise."It's a surprise you might expect to be widespread. For decades, disruptive events like storms and power outages have been anecdotally linked to a spike in birth rates nine months later. Couples are stuck inside and bereft of distractions, and so, the theory goes, nature takes its amorous course.