Final answer:
Breastfeeding inhibits the secretion of GnRH, reducing the chances of pregnancy.
Step-by-step explanation:
One is less likely to become pregnant while nursing because breastfeeding inhibits the secretion of GnRH (gonadotropin-releasing hormone) from the hypothalamus. When a mother breastfeeds, it stimulates the release of a hormone called prolactin, which suppresses GnRH secretion. GnRH is responsible for initiating the menstrual cycle and ovulation, so when its secretion is inhibited, it reduces the chances of getting pregnant.
For example, when a mother exclusively breastfeeds on demand without any supplementing of formula or solid foods, her prolactin levels remain high, and the frequency of her ovulation is significantly reduced, making it less likely for her to conceive.