Abstract: A mattress device designed for treating a pregnant woman by releasing the pressure ordinarily produced by the pregnant uterus and the abdominal wall on the abdominal aorta, thereby helping to prevent complications of pregnancy, such as toxemia and fetal distress. The device comprises a thick mattress-like member having an inflated ring extending through the mattress with a chamber formed on the central portion of the ring. The chamber is open at the top for receiving the pregnant uterus of a woman lying in the prone position, with her abdominal wall floating freely in the chamber. The inflated ring is filled to an air pressure which provides a body support that compensates for the heavier weight around the midsection. The combination of the variable air pressure of the ring and different sizes and shapes of such ring permit a mattress support well adapted to the varied sizes and shapes of the pregnant uterus while also enabling the abdominal wall to float freely in the chamber.