Postnatal Developmental Changes in the Pituitary-Ovarian Axis in Preterm and Term Infant Girls

Abstract

The period of postnatal pituitary activation has been well characterized in infant boys and is considered to be an important phase in future reproductive development. However, the possible importance of this activation in future female reproductive development is not understood. A number of clinical markers, including serum follicle-stimulating hormone (FSH) and anti-Múllerian hormone (AMH) levels, and the antral follicle count (visualized by ultrasonography) play a role in postnatal pituitary activation. Serum AMH levels strongly correlate with the antral follicle count in the follicular phase of the menstrual cycle. This longitudinal study compared postnatal developmental changes in the pituitary -ovarian axis in full-term and premature infant girls. A total of 63 infant girls were divided into the following 3 cohorts according to gestational age (GA) at birth: full term (FT; n = 29; GA, 37–42 weeks), near term (NT; n = 17; GA, 34–37 weeks), and preterm (PT; n = 17; GA, 25–34 weeks). Examinations were performed during the first week of life (D7), with subsequent monthly follow-up to 6 months of chronological age (M1–M6) and reexaminations at the corrected age of 14 months (cM14). The primary study outcome measures assessed at the follow-up examinations were levels of urinary FSH and serum AMH and the number of antral follicles. The postnatal FSH surge was significantly stronger and more prolonged among both NT and PT girls compared with FT girls (P ≤ 0.001). A rise in levels of AMH and increased folliculogenesis occurred in all 3 groups after the FSH surge. There was a delay among both NT and PT girls in follicular development compared with FT girls, with a temporal association between a decrease in the high FSH levels around the 40th postmenstrual week and the ultrasonographic appearance of antral follicles and increased AMH levels. These findings demonstrate a temporal relationship between the postnatal FSH surge and transient ovarian stimulation in term and PT girls. The strong FSH surge in premature girls may result from delayed ovarian folliculogenesis shown by the absence of antral follicles and low AMH levels.