Decidual Reaction

Definition - What does Decidual Reaction mean?

A decidual reaction is the transformation of the lining of the endometrium into the decidua, a thickening in the area where the implantation of a blastocyst has occurred. The newly decidualized cells provide nutrients for the growing embryo until the placenta has developed.

If the decidual reaction does not thicken to more than 2mm (which is considered a poor decidual reaction), it could indicate a potential miscarriage.

FertilitySmarts explains Decidual Reaction

The reaction takes place as a result of a hormonal release after implantation occurs within the uterine lining and these structural and functional changes that occur are important for the future formation of the placenta.

With a decidual reaction, the cells of the endometrium become enlarged and they begin to thicken, forming the different layers of the decidua: basalis, capsularis, and parietalis. These layers are one of the first important signs of pregnancy that can often be seen via transvaginal ultrasound.

A failed thickening of the decidua basalis, the third layer, has been seen in some miscarried pregnancies while regular thickening was seen in healthy pregnancies.

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