Relaxin in pregnancy: a narrative review of a pleiotropic molecule.

Introduction: Relaxin is a hormone primarily produced by the corpus luteum during pregnancy, and it plays a critical role in various physiological processes related to pregnancy and childbirth.

Evidence acquisition: Studies have suggested a possible link between relaxin levels and preterm birth. Relaxin's effects on the cervix and pelvic ligaments suggest it could influence the mode of delivery. Higher relaxin levels have been hypothesized to facilitate vaginal delivery by promoting cervical ripening and softening of the pelvic ligaments, thereby reducing the need for cesarean sections. The involvement of relaxin in extracellular matrix remodeling suggests it could play a role in placental attachment. Some experimental studies have proposed that aberrant relaxin signaling might contribute to the development of placenta accreta by influencing the invasive properties of trophoblast cells.

Evidence synthesis: The current evidence on relaxin's role in preterm birth, mode of delivery, and placenta accreta is not definitive. While there are plausible mechanisms by which relaxin could influence these outcomes, clinical studies have yet to provide strong, consistent evidence. Future research should focus on well-designed, large-scale studies to better understand the relationship between relaxin levels and these critical pregnancy outcomes.

Conclusions: The focus of this review is to evaluate relaxin as a potential biomarker and its potential future therapeutic applications during pregnancy and consider the limitations that must be addressed in future studies.