The period after childbirth, known as postpartum amenorrhea, is highly variable for new parents, especially those who are breastfeeding. The return of a regular menstrual cycle is a gradual process influenced by individual body chemistry and infant feeding patterns. For many, the experience is confusing, often involving inconsistent bleeding that makes it seem as though the period is starting and stopping erratically. Understanding the hormonal shifts that govern this period explains why the menstrual cycle often feels so unpredictable while nursing a baby.
The Hormonal Mechanism Delaying Menstruation
Breastfeeding directly influences the body’s reproductive hormones, creating a temporary state of infertility. The act of an infant suckling triggers the release of prolactin from the pituitary gland. While prolactin’s primary role is to stimulate milk production, its elevated levels suppress the pulsatile release of Gonadotropin-Releasing Hormone (GnRH) in the brain.
GnRH normally signals the pituitary gland to release the ovarian-stimulating hormones, Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH). By dampening the GnRH signal, prolactin keeps FSH and LH levels too low to initiate a normal ovulatory cycle and subsequent menstruation.
Factors That Trigger the Cycle’s Return
The menstrual cycle typically resumes when the prolactin-driven suppression of reproductive hormones begins to weaken. This often happens when the frequency and duration of nursing decrease, lowering overall prolactin levels. A significant change is the lengthening of the time between milk removals, especially during the nighttime.
When a baby starts sleeping longer stretches or night-weaning, the drop in nocturnal prolactin peaks signals that the intense demand for milk is lessening. Introducing solid foods or supplementing with formula also reduces the time an infant spends suckling. These changes lessen the hormonal signal, allowing FSH and LH release to increase enough to restart the menstrual cycle. The return of a period is a consequence of a shift in the infant’s feeding pattern.
Understanding Erratic Cycles While Nursing
The initial return of bleeding while nursing rarely means an immediate return to a predictable, pre-pregnancy cycle. The first cycles are often anovulatory, meaning they occur without the release of an egg. Without ovulation, the body does not produce the necessary amount of progesterone, the hormone that stabilizes the uterine lining.
Instead of a full, regulated menstrual flow, the uterine lining may shed erratically due to unopposed estrogen stimulation, resulting in spotting or bleeding that seems to come and go. Cycles may be very long, with months skipped between bleeds, or they may be unusually short. Some people experience a light flow one month, followed by a heavier flow the next, or simply a few days of spotting instead of a true period.
Even when ovulation does occur, the resulting cycle may suffer from a luteal phase defect, where the progesterone-producing structure is not fully functional. This defect can lead to a shorter time between ovulation and the next bleed, or cause spotting before the period starts. The irregularity is a sign that the reproductive system is gradually regaining its function, still influenced by fluctuating nursing hormones. The “come and go” pattern reflects the body’s slow transition back to full fertility.
When Bleeding Requires Medical Evaluation
While irregularity is common during the return of the cycle while nursing, certain types of bleeding require prompt medical attention. Heavy bleeding that does not slow down, such as soaking through multiple sanitary pads in an hour for two or more consecutive hours, signals potentially dangerous blood loss. Passing blood clots larger than a golf ball should be discussed with a healthcare provider.
Any bleeding accompanied by systemic symptoms like a fever over 100.4°F (38°C) or a foul-smelling vaginal discharge could indicate a uterine infection. Severe or continuous abdominal pain that does not resolve with typical pain relief also warrants medical evaluation. If you experience sudden dizziness, a rapid heartbeat, or feel faint, seek emergency care, as this signals significant blood loss or other complications.