New ADIPS GDM diagnoctic criteria are based upon 24-28 week glucose data but many clinics use the same criteria at booking. The aim of this study was to test the feasibility of a RCT of treating GDM at booking or awaiting the oral glucose tolerance test at 24-28 weeks. Consecutive women booking <20 weeks gestation, with at least one GDM risk factor, were invited into the study. All women completed a questionnaire, anthropometry and an oral glucose tolerance test (OGTT) with additional fasting blood sampling. Women with GDM at booking were randomised to either clinic management or awaiting the results to a repeat 24-28 week OGTT, along with those women without Booking GDM. Birth and baby anthropometric data were collected. All babies had a heel prick glucose at 1-2 hours. A survey of study procedures was undertaken postnatally. Of the 607 women approached, 100 were consented to enter the RCT. The main reason for exclusion was gestation 20+/40 (290), only 28 refused overall, 78 had previously been tested or refused OGTT and 95 had no risk factors. Of those consenting, 28 were withdrawn (eg 12 did not attend OGTT). There were 22 women with Booking GDM: (vs no GDM respectively: 50% vs 56% European, age- 30±6 vs 29±6 years, BMI- 32.4±7.1 vs 29.4±7.1 kg/m2 NS) and 17 (77%) had an elevated fasting glucose. Of the 11 randomised to treatment deferral, 10 (92%) still had GDM at the 24-28 week OGTT. Women with GDM at booking had lower adiponectin (8.2±2.8 vs 11.8±7.6 ug/ml p=0.044) but higher insulin (146±89 vs 81±54 pmol/l p<0.001), and leptin (63±28 vs 47±26 ng/ml p=0.026). We conclude that an RCT of treating GDM at booking is feasible. Women with GDM at booking are relatively insulin resistant, hyperleptinaemic and hyperinsulinaemic compared with other women.