Feeling super-tetchy in your first trimester? Blame your hormones as well as your amygdala. In the first 12 weeks of pregnancy you have a huge surge of progesterone, which rises around 40 times more than it does during a menstrual cycle. And this can make you feel emotional and stressed. Just remember that all this progesterone is doing a vital job, preparing your uterus for your baby, increasing the blood flow to your womb, and helping to establish your placenta.