Table 2.

Categorization scheme of Kenney and Doig [1] modified by Schoon et al. [2,3].

Category	Microscopic Findings and Additional Factors	Estimated Foaling Rate *
I	No significant alterations	>80–90%
IIa	Mild endometritis OR Mild endometrosis OR Mild lymphatic lacunae OR Partial endometrial atrophy during the late breeding season	50–80%
IIb	Moderate endometritis OR Moderate endometrosis OR Moderate lymphatic lacunae OR Barrenness ≥2 years OR Combined presence of two category IIa findings	10–50%
III	Marked endometritis OR Marked endometrosis OR Marked lymphatic lacunae OR Deep endometrial atrophy during the breeding season OR Combined presence of ≥3 category IIa or ≥2 category IIb or III findings	<10%

* Term pregnancy and delivery of a live foal.