Investigation of the human corpus luteum by ultrasonography: a proposed scheme for clinical investigation.

The corpus luteum was investigated in 18 women undergoing hysterectomy. Preoperative ultrasonography with measurements was performed before the corpus luteum was extirpated, weighed, inspected and the diameters were measured. The concentrations of progesterone and estradiol were also determined in peripheral serum. The ultrasound pictures show that the corpus luteum has a slightly cloudy central part, which can vary from hypoechoic to hyperechoic. The peripheral part (corpus luteum 'wall') has a stronger echo and the maximal and minimal thicknesses can be measured. The results showed correlations between ultrasound measurements and anatomical measurements for wall thickness, outer diameter, inner diameter and wall area of the corpus luteum (n = 12, p < 0.02-0.0001). Moreover, all mid-luteal corpora lutea with a hypoechoic central part (five of 13 women) on ultrasound scan had a cystic central structure. Based on these findings, we suggest that an ultrasound investigation of the corpus luteum in the mid-luteal phase should use the following criteria to classify it into four types. Type a: hypoechoic central part with wall of < 3 mm; type b: hyperechoic central part with wall of < 3 mm; type c: hypoechoic central part with wall of >or= 3 mm; and type d: hyperechoic central part with wall of >or= 3 mm. The finding of a hypoechoic central region with a thin wall (< 3 mm) may indicate corpus luteal insufficiency, since significantly lower serum progesterone levels were found in women with this type of corpus luteum.