Human fetal membranes inhibit spontaneous uterine contractions.

Fetal membranes are postulated to play a role in paracrine signaling during the initiation of labor in women. We developed a dual chamber-fetal membrane-uterine muscle model to study the effect of human fetal membranes on spontaneous uterine contractions. In this model, full-thickness fetal membranes (amnion, chorion, and maternal decidua) are sealed into a Plexiglass chamber. The membranes partition the chamber into a maternal and fetal compartment. Chorion and decidua face the maternal side, and amnion faces the fetal side. An estrogenized rat uterine muscle strip is anchored into the maternal side as a bioassay to measure effects of fetal membranes on uterine contractions. Fetal membranes cause a 40% decrease in uterine contractions compared to basal condition (no membranes). Inhibition is reversible after removal of the membranes. The inhibition is specific to the chorion/decidual side because reversal of membranes with amnion toward the muscle did not show inhibition. Uterine contractions did not change over time in control chambers in which Parafilm substituted for membranes. A model for studying paracrine regulation of uterine contractions by human fetal membranes has been developed. The model provides evidence that fetal membranes inhibit uterine contractions. This inhibitory effect may contribute to uterine quiescence during pregnancy.