Sex during pregnancy - oh yes indeed!

No mystery here, pleasureglans,

High levels of estrogen and progesterone, plus no fear of getting knocked up - at least after the first trimester of morning sickness [for some, not all of course] abates. Also, pregnancy confers increased levels of relaxin [yep, that's the name of a peptide, go figure] which makes everything sorta loosey-goosey - perfect for those who wish to have anal sex but who normally feel a little...retentive, pun intended .

Of course there are some women who don't feel too good - everything from pre-eclampsia, morning sickness, exhaustion to those who start dilating too soon and have to lie perfectly still for weeks - but for most healthy pregnancies, the second trimester can be positively glorious from a sexual perspective.

And NO, your penis won't hurt the baby's head
The Love Goddess

I sure hope that doesn't mean they lose their concern over STD's in all that new enthusiasm. Actually, what I hear from women is that they become even more concerned about the possibility of their SO's having contracted an STD that might affect their baby, in utero. It would seem that these same women, though their enthusiasm for sex might increase, would still be very cautious about contracting STD's.