title: The association of progesterone, infant formula use and pacifier use with the return of menstruation in breastfeeding women: a prospective cohort study.
abstract: OBJECTIVE
  This study sought to explore hormonal and postnatal factors, which are associated with the return of menstruation in breastfeeding mothers.
  
  
  METHODS
  A prospective cohort study in Bristol, UK. Ninety-one breastfeeding mothers of mixed parity were recruited at community-based antenatal clinics. Eighty-five mothers completed all stages and informed us about the return of menstruation. Data were collected from interviews and questionnaires antenatally, immediately postnatally, and 1 week, 4 weeks and 6 months later. Blood samples were taken at all time points except at 6 months. Associations between hormone levels, postnatal factors and the return of menstruation were explored using univariate and multivariate statistical survival analysis.
  
  
  RESULTS
  Sixty-five (76%) mothers were still breastfeeding at 6 months and 46 (54%) of these were fully breastfeeding (not giving formula milk); 21 (32%) mothers started menstruating in the first 6 months whilst they were still breastfeeding and 14 were fully breastfeeding at 6 months. Survival analysis modelling showed that formula use (RR=4.27; 95% CI=1.89, 9.67), pacifier (dummy) use (RR=3.26; 95% CI=1.35, 7.84) and lower postnatal progesterone levels (P=0.006) each made a significant contribution to the chance of earlier resumption of menstruation. Prolactin and oestradiol levels showed no associations with the return of menstruation.
  
  
  CONCLUSIONS
  Higher postnatal progesterone levels are associated with delayed menstruation; while the use of pacifiers and infant formula milk are associated with an earlier return to menstruation.
authors.affiliation: Centre for Child and Adolescent Health, University of Bristol, Hampton House, Cotham Hill, Bristol BS6 6JS, UK. jenny.ingram@bristol.ac.uk
authors.forename: Jenny
authors.initials: J
authors.lastname: Ingram
authors.forename: Linda
authors.initials: L
authors.lastname: Hunt
authors.forename: Mike
authors.initials: M
authors.lastname: Woolridge
authors.forename: Rosemary
authors.initials: R
authors.lastname: Greenwood
mesh_terms: D000328:Adult; D001724:Birth Weight; D001942:Breast Feeding; D015331:Cohort Studies; D004958:Estradiol / Q000097:blood; D005260:Female; D005865:Gestational Age; D006801:Humans; D041943:Infant Formula; D008297:Male; D008598:Menstruation; D041361:Pacifiers; D010298:Parity; D049590:Postpartum Period / Q000097:blood; D011374:Progesterone / Q000097:blood*; D011388:Prolactin / Q000097:blood; D011446:Prospective Studies; D012044:Regression Analysis; D011795:Surveys and Questionnaires; D013997:Time Factors
chemical_list: D011374:Progesterone; D004958:Estradiol; D011388:Prolactin