In plain words
Progesterone helps keep the uterus calm through most of pregnancy. Near the end, the uterus stops responding to it in the usual way. Scientists call this functional progesterone withdrawal. In humans, the blood level of progesterone does not fall sharply before birth. The change happens in the uterus's receptors instead. At the same time, the uterus becomes more sensitive to and makes more . Together these shifts help labor begin. A mother does not feel this change directly. It is part of the body's slow preparation for birth. Researchers see it as one reason labor can start on its own, without a clear trigger.
The deeper version
In most mammals, parturition follows a fall in serum progesterone. In humans, serum progesterone stays high until delivery, and the withdrawal is functional. The shifts toward progesterone receptor A expression relative to receptor B, which reduces progesterone's suppressive effect. Mesiano and colleagues (Journal of Clinical Endocrinology and Metabolism, 2002) showed that progesterone receptor A expression coordinates this withdrawal with estrogen activation. Smith (New England Journal of Medicine, 2007) reviewed how these changes combine with rising estrogen activity, greater oxytocin receptor expression, prostaglandin synthesis enzymes, and connexin-43 gap junctions. The open question is whether the process is a true loss of progesterone signaling or a shift in receptor balance, and how much local progesterone availability changes before labor.
Where it comes up
- Signs labor is startingGetting Ready for Birth
- Braxton Hicks and practice contractionsPregnancy: Your Body
- Short cervix and signs of preterm laborPregnancy: Your Body
What mothers here say about functional progesterone withdrawal
No one has posted under this term yet.
Sources
- Mesiano S and colleagues — Progesterone withdrawal and estrogen activation in human parturition are coordinated by progesterone receptor A expression in the myometrium. Journal of Clinical Endocrinology and Metabolism, 2002
- Smith R — Parturition. New England Journal of Medicine, 2007