MMP9 and placenta accreta: Importantly, the hormonal regulation of MMP-9 appears context- and tissue-specific, in the endometrium, P4 receptor activation suppresses MMP-9 during the secretory phase to maintain stromal integrity and prevent premature breakdown of the ECM, whereas in states of progesterone resistance (e.g., preterm labor, placenta accreta) enhanced MMP-9 expression is frequently observed.