Plasma prolactin/oestradiol ratio at 38 weeks gestation predicts the duration of lactational amenorrhoea

Hum Reprod. 2001 Dec;16(12):2540-5. doi: 10.1093/humrep/16.12.2540.


Background: Fully breastfeeding women experience an amenorrhoea of variable duration. Our aim was to identify in pregnancy, endocrine markers that could predict the duration of subsequent lactational amenorrhoea.

Methods: We studied 17 healthy women at 34 and 38 weeks gestation, and 1 and 3 months post-partum. The women fully breastfed until 6 months post-partum. During pregnancy, prolactin (PRL), oestrogens (total oestradiol, unconjugated oestrone, unconjugated oestriol), sex hormone binding globulin (SHBG), dehydroepiandrosterone sulphate (DHEA-S), progesterone and placental lactogen, and during post-partum PRL, oestrogens and SHBG, were measured. Free oestradiol in pregnancy and post-partum was calculated.

Results: Ten women experienced long (>6 months) and seven experienced short (<6 months) lactational amenorrhoea. At 38 weeks gestation, the women who experienced a long lactational amenorrhoea had twice as much PRL, about half the total oestradiol, lower SHBG concentration (P < 0.05, Student's t-test, Bonferroni modification) and similar free oestradiol concentration, compared with those who experienced short lactational amenorrhoea. The difference in PRL concentration persisted in post-partum postsuckling samples.

Conclusion: At 38 weeks gestation, the ratio PRL/oestradiol identified all individual women according to the subsequent duration of their lactational amenorrhoea, suggesting that duration of lactational amenorrhoea is conditioned during pregnancy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Amenorrhea*
  • Dehydroepiandrosterone Sulfate / blood
  • Estradiol / blood*
  • Estriol / blood
  • Estrone / blood
  • Female
  • Gestational Age*
  • Humans
  • Placental Lactogen / blood
  • Postpartum Period*
  • Pregnancy
  • Progesterone / blood
  • Prolactin / blood*
  • Sex Hormone-Binding Globulin / analysis
  • Time Factors


  • Sex Hormone-Binding Globulin
  • Estrone
  • Progesterone
  • Estradiol
  • Dehydroepiandrosterone Sulfate
  • Prolactin
  • Placental Lactogen
  • Estriol