Sonographic study of the decidua basalis in early pregnancy loss

To describe the sonographic findings in the decidua basalis layer in spontaneous early pregnancy loss and to compare them with those in normal pregnancy.

We reviewed 119 scans at 4-10 weeks' gestation from 110 patients who miscarried clinically at less than 13 weeks' gestation and 132 scans also at 4-10 weeks from 98 patients who had normal uncomplicated term pregnancies. The thickness and echogenicity of the decidua basalis layer were compared between pregnancies which suffered early loss and normal controls.

Relative thinning of the decidua basalis was observed in cases of early pregnancy loss from 5-6 weeks onwards when compared with normal pregnancies. In embryonic pregnancies that subsequently miscarried, the decidua basalis did not show the rising trend in thickness that was observed in normal pregnancies. Shortly before and after embryonic demise, the decidua appeared relatively more echogenic compared with that in normal pregnancy and the placenta showed areas of hypoechogenicity. Embryonic demise was followed by disorganization of the decidual layer, which became difficult to recognize. Pregnancy with an empty sac showed a more gradual trend in the thinning of the decidua basalis, but the uniformity and echogenicity of the layer appeared to be relatively better preserved with time.

The decidua basalis layer in pregnancies that are destined to miscarry in the first trimester differs sonographically from that in normal pregnancies. The sonographic differences are suggestive of a defective decidual-placental complex resulting from deficient trophoblastic invasion.