Which hormone helps relax the uterus during pregnancy, reducing contractions and also relaxes the blood vessels, stomach and bowels?

• A. Estrogen
• B. Relaxin
• C. Progesterone
• D. Prostaglandins

Answer: (C)

Progesterone keeps the uterus calm during pregnancy by reducing the myometrium’s excitability and limiting receptors for contractions like oxytocin, which helps prevent premature contractions as the pregnancy progresses. Its smooth muscle–relaxing effect isn’t limited to the uterus—it also relaxes vascular smooth muscle and smooth muscle in the stomach and bowels, contributing to vasodilation and decreased GI motility. That combination of uterine quiescence and systemic smooth muscle relaxation fits the description in the question. Estrogen tends to promote uterine growth and can increase contractility, prostaglandins often trigger contractions, and relaxin mainly influences pelvic ligaments and tissues rather than directly keeping the uterus relaxed, making progesterone the best fit.