A theory I heard on this (about twenty years ago) is that tickling with women at least is (surprisingly) a defense mechanism meant to protect virgins from unwanted advances. I heard this on Dr. Dean Edell years ago. The laughter was meant to have a negative effect on the male. I personally am not saying yes or no to this, just what I heard. Yes with us tickling is a turn on not a turn off, but to others it is a turn off. Obviously it is more to shake off insects way back in primitive days, but it may have become adapted to other uses because it is still a human reflex action.
So to apply this theory to pregnant women. I can see that yes a pregnant woman could become more ticklish as a natural reflex action to protect the baby. And in addition I can see a pregnant woman needing added protection vs. insects or other small creepy crawlies. Yet with me being a guy and never have been pregnant I can't really speak from personal experience.
Ladies? Any insights here?