When I had a midwife suggest it (I'm assuming you're talking for natural induction purposes?), I was told for it to have any significant effect you'd need to be doing the deed every hour for twelve hours.

Now that's lots
OMG...That's amazing who at 9 months pregnant would have the energy to be DTD every hour for 12hours

I guess if this is the case sex wont be helping me much, hubby is away from home for 15-16hrs per day 6 days a week so it only leaves us one day and neither of us would have the energy for that......

That sure is lots...hahahaha!!!