I always wonder: the law says jobs can't discriminate, but if a woman became pregnant during her probation period I'm willing to bet a lot of companies would find an excuse to let her go. Wouldn't they?
I worked with someone who announced her pregnancy to the company just after they'd made her permanent. Everyone was whispering about it behind her back, saying she'd been sneaky etc which I thought was really unfair. But because of this, I personally would feel bad if I became pregnant and requested maternity leave unless I'd worked somewhere two years or so.