title: Mechanism of action of progesterone as contraceptive for lactating women.
abstract: Progesterone vaginal rings releasing 5-15 mg/day were tested as a contraceptive for lactating women. Progesterone plasma levels achieved ranged from 10 to 20 nmol/L. Pregnancy rates at the end of the year were less than 1% and 39% in treated (n = 210) and untreated (n = 236) nursing women, respectively. Around 70% of treated and 30% of untreated women were amenorrheic at 8 months post partum. The endocrine profile during the first 8 months post partum was assessed in 36 treated and 28 untreated nursing women. Pre- and postsuckling prolactin (PRL) levels were measured at 1600 hr at fortnightly intervals and E2 determinations and ovarian ultrasound were performed twice a week. Prolactin increases in response to suckling and postsuckling PRL levels were higher, E2 levels were lower, and follicular growth was arrested at earlier stages in progesterone-treated than in untreated women. The pattern observed in progesterone-treated women was similar to that in prolonged lactational amenorrhea. This suggests that progesterone increases the sensitivity of the breast-hypothalamic-pituitary system to suckling and reinforces the mechanism of lactational infertility.
authors.affiliation: Instituto Chileno de Medicina Reproductiva, Consultorio de Planificación Familiar, Santiago, Chile.
authors.forename: S
authors.initials: S
authors.lastname: Díaz
authors.forename: P
authors.initials: P
authors.lastname: Miranda
authors.forename: A
authors.initials: A
authors.lastname: Brandeis
authors.forename: H
authors.initials: H
authors.lastname: Cárdenas
authors.forename: H B
authors.initials: HB
authors.lastname: Croxatto
mesh_terms: D001942:Breast Feeding; D003270:Contraceptive Agents / Q000494:pharmacology*; D003273:Contraceptive Devices; D005260:Female; D006801:Humans; D007774:Lactation / Q000097:blood; D006080:Ovarian Follicle / Q000000981:diagnostic imaging; D011374:Progesterone / Q000008:administration & dosage / Q000494:pharmacology*; D011388:Prolactin / Q000097:blood; D014463:Ultrasonography
chemical_list: D003270:Contraceptive Agents; D011374:Progesterone; D011388:Prolactin