Birth has been compared to climbing a mountain or completing a marathon. Being physically fit is an advantage. Exercise generally improves pregnancy, birth and newborn outcomes for people with normal pregnancies. There may be a protective factor for gestational diabetes, congenital anomalies, miscarriage, placental problems, intrauterine growth restriction, high blood pressure or fetal death. Evidence suggests that abnormal heart rates, cord entanglement, and the presence of meconium are significantly reduced. While there is no increase in premies, there may be fewer postdate gestations.