Why breastfeeding suppresses ovulation: prolactin and GnRH
When a baby suckles (feeds on the nipple), prolactin (the milk-making hormone) rises and tends to suppress GnRH (gonadotrophin-releasing hormone), which can suppress ovulation in some mothers.
Remember
Suckling lowers dopamine, so prolactin rises, and the high prolactin suppresses GnRH, and so FSH and LH (follicle-stimulating hormone and luteinising hormone) and ovulation. The effect is variable, so breastfeeding alone is not reliable contraception.
Memory aid
baby suckles, dopamine brake off, prolactin up, GnRH down, no ovulation
The chain runs in order from the baby suckling to no ovulation.
The hypothalamus (the part of the brain that controls the pituitary gland) produces dopamine, and dopamine normally inhibits prolactin release from the anterior pituitary. Suckling inhibits that dopamine release. This removes the brake, so prolactin is produced and milk production is maintained.
High prolactin then tends to suppress the secretion of GnRH from the hypothalamus. GnRH is the pulsing signal that tells the anterior pituitary to release FSH and LH (follicle-stimulating hormone and luteinising hormone). These hormones grow the ovarian follicles (the fluid-filled sacs that hold the eggs) and trigger ovulation. With fewer GnRH pulses, FSH and LH fall, the follicles do not mature, and there is no LH surge (the sudden rise in LH that releases the egg).
Ovulation is suppressed, which is why periods often do not return. This state is called lactational amenorrhoea (the absence of periods while breastfeeding). This suppression of ovulation is a central effect: it starts in the brain rather than the ovary. The exact link between suckling and GnRH is still being worked out.
The effect is strongest with frequent, exclusive feeding (breast milk only), and it fades as feeds become less frequent. It varies between women, so a woman who is breastfeeding can still ovulate, sometimes before her first period.
Key facts
- The chain
- Suckling lowers dopamine, so prolactin rises; GnRH pulses become less frequent, FSH and LH fall, and ovulation is suppressed.
- Site of action
- The hypothalamus, where raised prolactin reduces GnRH pulses, so the problem starts in the brain rather than the ovary.
- Dopamine
- Dopamine from the hypothalamus normally inhibits prolactin release, and suckling inhibits that dopamine release.
- Feeding pattern
- It is strongest with frequent, exclusive feeding and fades as feeds become less frequent.
- Not guaranteed
- Ovulation can occur before the first period, so breastfeeding or having no periods alone is not reliable contraception.
Exam traps
- Oxytocin, the other hormone of breastfeeding, is released with suckling and causes milk ejection (let-down), but it does not directly block follicle development; the effect on ovulation comes from a weaker GnRH signal from the hypothalamus.
- Suckling does not reduce prolactin, and prolactin does not stimulate GnRH: suckling raises prolactin, and the raised prolactin suppresses GnRH.
- Dopamine release does not increase with suckling: suckling reduces dopamine secretion from the hypothalamus so that prolactin can rise, because dopamine normally restrains prolactin release. A raised dopamine level would be the opposite direction of change.
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