The relationship of IUD dimensions to event rates

The relationship of horizontal-to-vertical ratio (HVR) of 14 commonly used IUDs was compared to medical removal and expulsion rates. A significant positive statistical correlation between IUD HVR and medical removal rate existed. However, no correlation existed between HVR and expulsion. A ratio of about 0.5 for multiparous and 0.7 for nulliparous women less frequently in medical removal of the device. The endometrial cavity length sizes have boundary values on IUD width of 15-18 mm for nulliparae and 18-25 mm for multiparae. The endometrial cavity is thus functionally an isosceles triangle or isosceles trapezoid.