Trilaminar Endometrium

Definition - What does Trilaminar Endometrium mean?

A trilaminar endometrium refers to an inner uterine lining that has a triple-line pattern as seen on an ultrasound examination. This type of endometrium is typically thick and receptive enough to allow for successful embryo implantation. A trilaminar endometrial pattern correlates with higher clinical pregnancy rates in frozen embryo transfer (ET) cycles. In contrast, an endometrium that lacks the triple-line pattern interferes with the implantation of the embryo and thus negatively impacts pregnancy rates.

FertilitySmarts explains Trilaminar Endometrium

A trilaminar endometrium usually has a thickness of around 7 and 14 mm with a triple-line configuration, which means that it contains a hyperechoic (usually displayed as light) line in the middle surrounded by two more hypoechoic (darker) lines as observed on an ultrasound.

On the other hand, when the endometrial thickness reduces to less than 7 mm, its functional layer becomes deficient, causing the embryo to implant much closer to the arteries that spiral around and supply the deepest layer of the endometrium. The extremely high oxygen levels near thIs very bottom endometrial layer could be detrimental to the embryo compared with the usual low oxygen tension of the surface endometrium.

However, surprisingly, even a thin endometrium can display a triple line pattern, and thus still confer high chances of clinical pregnancy during an IVF-ET cycle compared to a thinner endometrium without any triple line pattern. This shows that the endometrial pattern is more significant than the endometrial thickness, and a triple-line pattern on the day of hCG trigger shot is associated with increased implantation and pregnancy rates.

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