Relaxin is a reproductive hormone produced primarily by the ovaries and the placenta during pregnancy. It plays a major role in preparing the female body for childbirth. Understanding how long this hormone remains active after delivery is important because its effects extend into the postpartum recovery period. The continued presence of relaxin affects the mother’s musculoskeletal system as it transitions back to its non-pregnant state.
Relaxin’s Function During Pregnancy
Relaxin’s purpose during gestation is to facilitate the physiological changes required for delivery. The hormone works by softening and increasing the flexibility of the body’s connective tissues, specifically the ligaments and muscles. Relaxin is produced by the corpus luteum and later by the placenta, reaching its highest levels in the first trimester before a surge just before birth.
This flexibility is particularly important in the pelvis, where relaxin acts on the pubic symphysis to allow it to widen. It also helps to soften and widen the cervix, preparing the birth canal for the baby’s passage. Additionally, relaxin helps the uterine wall relax to prevent premature contractions in early pregnancy.
The Postpartum Timeline
Relaxin levels begin to decrease significantly immediately following childbirth, as the placenta—a major source of the hormone—is delivered. However, the hormone does not disappear overnight; it remains elevated above pre-pregnancy levels for a period of time.
It generally takes several months for relaxin to return to its non-pregnant baseline. The hormone can stay elevated for anywhere from five to twelve months postpartum, reflecting individual variation in how quickly the body metabolizes it.
For mothers who are breastfeeding, the return to baseline levels may be prolonged. Relaxin levels can remain higher while a woman is nursing, and even for a few months after she stops. This is thought to be related to the hormone’s role in promoting mammary gland relaxation and milk production.
While the initial drop is rapid, the clearance of the remaining hormone is a slower process. The effects of relaxin can persist for a full twelve weeks after birth, which is the approximate time the liver takes to metabolize the majority of the circulating hormone.
Physical Effects of Elevated Relaxin
The lingering presence of relaxin is responsible for the joint hypermobility and instability experienced by many new mothers. Since the hormone affects connective tissue throughout the entire body, joints like the knees and ankles can feel looser than usual. This increased flexibility, while necessary for birth, can temporarily predispose the body to strains or instability.
A common consequence is pelvic girdle pain (PGP) or lower back instability, resulting from the laxity of the pelvic ligaments. An unsteady or wobbly gait can persist as the body attempts to stabilize joints that were previously held more tightly. The combination of loose ligaments and the change in the body’s center of gravity means simple movements can feel challenging.
Because the ligaments are temporarily more supple, there is an increased risk of overstretching or injury, particularly during high-impact activities. New mothers are advised to engage in gentle, low-impact exercise to avoid overstressing joints. Focusing on strengthening the muscles surrounding the joints helps compensate for the temporary lack of structural support.