Physiology of Pregnancy By Raul Artal-Mittelmark, MD, Saint Louis University School of Medicine Reviewed / Revised May 2021 | Modified Sep 2022 View Patient Education Physiology Symptoms and Signs Diagnosis Topic Resources Pregnancy Gestation by LMP.. Melasma Linea Nigra Spider Angioma The earliest sign of pregnancy and the reason most pregnant women initially see a physician is missing a menstrual period.