It usually surfaces sometime in the 2nd trimester, sometimes earlier, sometimes later. Depends on how much stress the mother is in during the pregnancy. The stress can be caused by a multitude of factors, but usually is some sort of hormonal imbalance. At least, that's what the Drs all told us when my ex had it for the last two children we had. Can also be genetic, can be caused by foods and/or meds,dental stress/instability, can also be caused by being overweight, too.

During her fourth pregnancy, she was bed rested for the last trimester. Preeclampsia sucks, and can kill both mother and child if it's not handled properly. It almost killed our last two children, no.'s 4 & 5, and almost killed her, too.