Mood swings in pregnancy are caused by the rise of the hormones estrogen and progesterone. These increases can impact mood-regulating chemicals in your brain like dopamine and serotonin. Couple that with the stress and anxiety that can come with pregnancy, and you’ve got yourself a recipe for mood swings. In fact, early mood swings may be one of the first signs you’ll notice in your journey. But they don’t end in the first trimester; they can occur at any stage of pregnancy.