Association of pre-pregnancy low-carbohydrate diet with maternal oral glucose tolerance test levels in gestational diabetes. BMC pregnancy and childbirth BACKGROUND:Limited evidence exists on the correlation between the pre-pregnancy low-carbohydrate (LC) diet and maternal oral glucose tolerance test (OGTT) levels during pregnancy. Our aim was to compare the differences in maternal OGTT levels among women who had been diagnosed with gestational diabetes mellitus (GDM) during pregnancy and adopted different dietary patterns in the pre-pregnancy period. METHODS:A case-control study was conducted in 20 women with GDM who adhering to an LC diet (carbohydrate intake < 130 g/d) during pre-conception (LC/GDM,cases). Control subjects, who were matched in a 4:1 ratio, were 80 women with GDM and conventional diet (Con/GDM,control), and 80 women with conventional diet but without GDM (Con/Healthy,control). Women diagnosed with GDM using 75-g OGTT between 24 and 28 weeks of gestation. We used unadjusted raw data to compare the dietary composition data and biomarkers of the three study groups. RESULTS:The average pre-conception BMI in each group suggested a similar body size from the three study groups(19.12 ± 2.00 LC/GDM, 19.65 ± 2.32 Con/GDM, 19.53 ± 2.30 Con/Healthy; P = 0.647). Compared with the Con/GDM group, the OGTT-1 h and OGTT-2 h values in LC/GDM group were significantly higher (10.36 ± 1.28 mmol/L vs. 9.75 ± 0.98 mmol/L; 9.12 ± 0.98 mmol/L vs. 8.29 ± 1.06 mmol/L). Furthermore, the percentage of women who had more than one abnormal OGTT value (OGTT-1 h and OGTT-2 h) was 40% in the LC/GDM group, which was significantly higher than in the Con/GDM group (16.3%). CONCLUSIONS:We observed a relationship between the pre-pregnancy LC diet and more detrimental OGTT values in patients with GDM. This finding warrants further studies to understand the effect of pre-pregnancy LC diet practice on maternal glucose tolerance. 10.1186/s12884-022-05059-2