Poor Decidual Reaction

A poor decidual reaction occurs when the endometrium does not thicken as it should, leaving a growing embryo without the proper scaffolding for optimal development.

The decidual reaction is the process where maternal hormones, mainly progesterone, alter the endometrium following implantation. These changes result in the thickening, differentiation, and formation of the decidua around the gestational sac. It is the first evidence of pregnancy on an ultrasound.

The decidual thickness can be used as a predictor to determine the outcome of a pregnancy. Flawed decidua formation negatively affects the viability of the embryo in the uterus, and it can result in miscarriage. Other complications include preterm birth and intrauterine growth restriction.