When should preeclampsia screening be conducted?

It is important for the screening to be done early in pregnancy. And the reason for that is that we now have an effective way of reducing the risk of preeclampsia. It simply involves administration of low dose aspirin. And we know that it works only if we start it early in pregnancy, that is, prior to 16 weeks gestation. So, it's not only the best screen available in the first trimester, but it is critical to be done early in pregnancy.