Background and Objectives: The brain imaging of the pituitary gland in females has shown a change in pituitary size and volume in the female's population. It has been proven that the pituitary gland is affected by pregnancy, giving birth, and hormone-related factors. Therefore, this study aimed to evaluate the factors which may have an impact on the pituitary size in females at reproductive age and compare the pituitary size in females with a history of pregnancy, those at the postpartum period, and nullipara females. Materials and Methods: This population-based study was conducted on 208 healthy women aged 12-55 years old. Participants underwent cranial Magnetic resonance imaging (MRI), and pituitary diameters (craniocaudal, anteroposterior, and transverse) and volume were measured for each subject. The correlation of age, gravity, parity, lactation, and intake of oral contraceptives with pituitary size were analyzed. Results: One-hundred and eighty females met the criteria for participation. The pituitary volume correlated negatively with hormone-related factors. The gravity (r = -0.35) and parity (r = -0.35) had significant negative effects on the pituitary volume (p < 0.001). The use of oral contraceptives and lactation were also in negative correlation with the pituitary volume (r = -0.20, p = 0.006, r = -0.56, p < 0.001, respectively). The craniocaudal diameter was also affected by gravity (r = -0.62), parity (r = -0.57), intake of contraceptives (r = -0.32), and lactation (r = -0.70), p < 0.001. The anteroposterior diameter of the pituitary gland associated significantly with gravity (r = -0.19, p = 0.009), parity (r = -0.20, p = 0.007), and lactation (r = -0.25, p = 0.001). The transverse diameter of the pituitary gland also related negatively with reproductive factors such as gravity (r = -0.15, p = 0.04), parity (r = -0.17, p = 0.02), and lactation (r = -0.17, p = 0.02). The pituitary gland of nullipara females was the greatest in size. Recent pregnancy led to increased craniocaudal and anteroposterior diameters. Conclusions: In this study, we found a negative effect of pregnancy and giving birth on pituitary size. Nullipara females were found to have the greatest pituitaries, even greater than the females in the postpartum period.
Keywords: estrogen; gravidities; neuroimaging; parity; pituitary hormones; postpartum period.