Inclusion Criteria:  Gestational age: 37-42 weeks. Birthweight: 2500-4000 g.  Exclusion Criteria:  Neonates more than 6 hours of age at time of enrollment. Perinatal asphyxia or hypoxia (1 min Apgar scoring<7 points) Cardiac structural abnormalities detected by echocardiography except patent foramen ovale and patent ductus arteriosus Other clinically detected congenital malformations such as cleft lip and palate, omphalocele, meningocele, etc. Maternal history of gestational hypertension, gestational diabetes, hyperthyroidism, hypothyroidism, and autoimmune disease