Poor Decidual Reaction

Definition - What does Poor Decidual Reaction mean?

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.

FertilitySmarts explains Poor Decidual Reaction

The decidual reaction is an essential step in both the establishment and maintenance of pregnancy. The decidualized cells are responsible for providing nutrients for the embryo until the placenta develops, regulating the maternal immune system, and detecting the difference between high- and low-quality embryos.

The decidual reaction results in two layers during the 4th week of pregnancy. Visualization of these layers on ultrasound is indicative of the double decidual sac sign which is suggestive of a normal intrauterine pregnancy. Later on, a third layer develops.

When a decidual reaction of 2mm or less is seen on ultrasound, it is a troubling sign and is suggestive of an anembryonic pregnancy.
An anembryonic pregnancy is a situation where the gestational sac develops but the embryo does not.

Studies have shown that in some of the early pregnancies that have miscarried, the third layer of the decidua (basalis), did not show the rise in thickness that is seen in healthy pregnancies.

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