|European Society of Human Reproduction and Embryology (ESHRE) and the European Society for Gynaecological Endoscopy (ESGE)
- Class U0 - incorporates all cases with normal uterus.
- Class U1 - (Dysmorphic uterus) incorporates all cases with normal uterine outline but with an abnormal shape of the uterine cavity excluding septa. Class I is further subdivided into three categories
- Class U1a - (T-shaped uterus) characterized by a narrow uterine cavity due to thickened lateral walls with a correlation 2/3 uterine corpus and 1/3 cervix,
- Class U1b - (uterus infantilis) characterized also by a narrow uterine cavity without lateral wall thickening and an inverse correlation of 1/3 uterine body and 2/3 cervix
- Class U1c - (others) which is added to include all minor deformities of the uterine cavity including those with an inner indentation at the fundal midline level of less than 50 % of the uterine wall thickness.
- Class U2 - (septate uterus) internal indentation >50 % of the uterine wall thickness & external contour straight or with indentation <50 %
- Class U2a - (partial septate uterus) characterized by the existence of a septum dividing partly the uterine cavity above the level of the internal cervical os
- Class U2b - (complete septate uterus) characterized by the existence of a septum fully dividing the uterine cavity up to the level of the internal cervical os.
- Class U3 - (bicorporeal uterus) external indentation >50 % of the uterine wall thickness
- Class U3a - (partial bicorporeal uterus) characterized by an external fundal indentation partly dividing the uterine corpus above the level of the cervix
- Class U3b - (complete bicorporeal uterus) width of the fundal indentation at the midline >150 % of the uterine wall thickness) completely dividing the uterine corpus up to the level of the cervix
- Class U3c - (bicorporeal septate uterus) characterized by the presence of an absorption defect in addition to the main fusion defect.
- Class U4 - (hemi-uterus) incorporates all cases of unilateral formed uterus. Hemi-uterus is defined as the unilateral uterine development; the contralateral part could be either incompletely formed or absent.
- Class U4a - (hemi-uterus with a rudimentary (functional) cavity) characterized by the presence of a communicating or non-communicating functional contralateral horn
- Class U4b - (hemi-uterus without rudimentary (functional) cavity) characterized either by the presence of non-functional contralateral uterine horn or by aplasia of the contralateral part.
- Class U5 - (aplastic uterus) incorporates all cases of uterine aplasia, formation defect characterized by the absence of any fully or unilaterally developed uterine cavity.
- Class U5a - (aplastic uterus with rudimentary (functional) cavity) characterized by the presence of bi- or unilateral functional horn
- Class U5b - (aplastic uterus without rudimentary (functional) cavity) characterized either by the presence of uterine remnants or by full uterine aplasia.
- Class U6 - is kept for still unclassified cases.