How well does ultrasonographic measurement of endometrial thickness predict the results of histological dating?

In this study, transabdominal ultrasonographic measurement of endometrial thickness was performed prior to sampling of the endometrium for histological examination in regularly cycling women. In the natural cycles, the results of ultrasonography and histological dating were significantly correlated (r = 0.76, P less than 0.0001, n = 63). Endometrial histology was likely to be proliferative if the thickness was less than 8 mm, and likely to be secretory if the thickness was greater than 9 mm. However, for a given endometrial thickness, the stage of endometrial development appeared to vary widely, suggesting that ultrasonographic measurement of endometrial thickness cannot accurately predict the results of histological dating. In the second part of the study, endometrial thickness at a defined stage of histological development (results of histological dating between days LH + 4 and LH + 6) was compared in three types of cycles: natural (n = 13), clomiphene-stimulated (n = 12) and artificial (n = 22) cycles. The endometrial thickness (mean +/- standard deviation) in artificial cycles (9.9 +/- 1.3 mm) was significantly smaller than that in natural (11.3 +/- 1.4 mm) or clomiphene-stimulated (11.2 +/- 1.3 mm) cycles, but there was no difference in endometrial thickness between the latter two types of cycle. Our observations suggest that it is unlikely that ultrasonographic measurement of endometrial thickness can replace histological examination of the endometrium in the evaluation of the luteal phase.