The absence of a menstrual period while nursing a baby is commonly referred to as lactational amenorrhea. This biological event is a normal, expected physiological response that occurs as the body prioritizes milk production for the newborn. The term “amenorrhea” simply means the temporary lack of menstruation, and “lactational” indicates that it is directly caused by breastfeeding. Understanding the complex hormonal interactions that govern this pause provides insight into why and when the menstrual cycle will eventually resume.
How Breastfeeding Stops Your Period
The primary trigger for halting the menstrual cycle is the physical act of the infant suckling at the breast. This stimulation sends a signal to the brain, specifically to the pituitary gland, which responds by releasing the hormone prolactin. Prolactin’s main function is to stimulate the mammary glands to produce milk, but it also has a profound effect on the reproductive system.
Elevated levels of prolactin effectively suppress the pulsatile release of Gonadotropin-Releasing Hormone (GnRH) from the hypothalamus, which acts as the master regulator of the reproductive cycle. Without the proper signaling from GnRH, the pituitary gland does not release adequate amounts of Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH). These hormones are necessary to stimulate the ovaries to mature an egg, trigger ovulation, and subsequently build the uterine lining. By disrupting this hormonal cascade, frequent nursing prevents ovulation, and menstruation does not occur.
When Menstruation Typically Returns
The hormonal suppression that causes lactational amenorrhea is closely tied to the frequency and intensity of the suckling stimulus, meaning the return of menstruation is highly individualized. As the infant gets older and the pattern of feeding changes, the consistent high levels of prolactin begin to drop, allowing the reproductive hormones to gradually resume their normal rhythm. Longer stretches between feeds often signal the body that the intense demands of the newborn period are easing.
The introduction of solid foods, which naturally decreases the volume of breast milk the baby consumes, is a common factor leading to a menstrual return. Supplementing with formula or other liquids reduces the total time the baby spends at the breast, lowering the overall prolactin-stimulating signal. Night feeds are potent in maintaining high prolactin levels, so when a baby begins sleeping for longer stretches overnight, hormonal suppression can break down more quickly. Direct nursing is typically more effective at maintaining amenorrhea than exclusive pumping. While some mothers see their period return as early as a few months postpartum, for many who continue to nurse frequently, it may not resume until nine to eighteen months or even longer.
Breastfeeding as a Form of Birth Control
The temporary infertility associated with nursing is formally recognized as the Lactational Amenorrhea Method (LAM) for family planning. When used correctly, LAM is a highly effective, though temporary, form of contraception. For the method to be reliable, three strict criteria must be met simultaneously to ensure hormonal suppression prevents ovulation:
- The baby must be less than six months old, as nursing intensity naturally declines after this point.
- The mother must be amenorrheic (no bleeding after initial postpartum bleeding ceases).
- The baby must be exclusively or nearly exclusively breastfed, with frequent feeds day and night, without long intervals between sessions.
Fertility often returns before the first postpartum period because the body will ovulate before it sheds the uterine lining. This means pregnancy can occur before the first menstrual bleed, highlighting the need for vigilance when using LAM. As soon as any of the three criteria are no longer met—the baby turns six months, menstruation returns, or feeding becomes less frequent—backup contraception is necessary.