Does breastfeeding reduce luteinizing hormone (LH) and follicle‑stimulating hormone (FSH) levels?

Does Breastfeeding Reduce LH and FSH?

Yes, breastfeeding significantly reduces luteinizing hormone (LH) levels and suppresses gonadotropin release, while follicle-stimulating hormone (FSH) levels remain relatively normal during lactation. 1

Mechanism of Gonadotropin Suppression During Lactation

The hormonal changes during breastfeeding follow a specific pattern:

LH Suppression:

• Breastfeeding disrupts the pulsatile release of GnRH from the hypothalamus, which directly reduces LH secretion from the pituitary 2
• Basal LH concentrations are significantly lower than normal when ovarian activity is completely suppressed during lactation 3
• The suckling stimulus and prolactin elevation inhibit hypothalamic GnRH release, suppressing gonadotropin release 1
• LH levels remain low throughout lactation and only return to normal with the resumption of ovulatory cycles 4

FSH Levels:

• In contrast to LH, FSH levels remain at concentrations comparable to the follicular phase of normal ovulatory cycles throughout the postpartum period 4
• FSH concentrations during lactation are sufficient to induce follicle growth, but the inadequate pulsatile LH signal prevents normal ovulation 2
• FSH secretion is not significantly suppressed during breastfeeding 3

The Physiological Pathway

The mechanism works through this cascade:

1. Suckling stimulus → increases prolactin and PTH-rP with each feeding 1
2. Prolactin elevation → inhibits hypothalamic GnRH release 1
3. Reduced GnRH pulsatility → decreases LH secretion (FSH less affected) 2
4. Low LH → inadequate stimulation of ovarian follicles despite normal FSH 2
5. Result: Suppressed ovulation and lactational amenorrhea 5

Clinical Implications

Contraceptive Effect:

• The lactational amenorrhea method (LAM) is at least 98% effective when three conditions are met: baby under 6 months, mother still amenorrheic, and exclusive/quasi-exclusive breastfeeding on demand 5
• This contraceptive effect is directly related to the suppression of LH and disruption of normal ovulatory cycles 5

Return to Fertility:

• When the suckling stimulus declines sufficiently, normal preovulatory LH surge can occur, allowing ovulation 2
• LH levels rise more rapidly in non-breastfeeding mothers, returning to normal by 3 weeks postpartum, compared to prolonged suppression in breastfeeding mothers 4

Important Caveats

The degree of gonadotropin suppression varies:

• During complete ovarian suppression in breastfeeding women, two patterns exist: 76% show low-frequency, low-amplitude LH pulses, while 24% show LH patterns similar to normal follicular phase 3
• Individual women may show either or both patterns during the period of ovarian suppression 3
• The mechanism does not appear to involve prolactin, dopamine, or opiates alone, though a combination might be involved 2

The key distinction is that breastfeeding selectively suppresses LH while maintaining relatively normal FSH levels, creating a hormonal environment that prevents ovulation but allows some follicular development.