In the United States, most obstetricians prefer universal screening with a screening glucose challenge test.[27] In the United Kingdom, obstetric units often rely on risk factors and a random blood glucose test.[21][28] The American Diabetes Association and the Society of Obstetricians and Gynaecologists of Canada recommend routine screening unless the woman is low risk (this means the woman must be younger than 25 years and have a body mass index less than 27, with no personal, ethnic or family risk factors)[5][26] The Canadian Diabetes Association and the American College of Obstetricians and Gynecologists recommend universal screening.[29][30] The U.S. Preventive Services Task Force found there is insufficient evidence to recommend for or against routine screening.[31]