Introduction Face-it is a randomized controlled trial for women with recent gestational diabetes mellitus (GDM) and their families designed to evaluate the effect of a health promotion intervention on type 2 diabetes mellitus (T2DM) risk and quality of life. This study examined (1) the penetration and participation rates for the Face-it trial, (2) the characteristics of the participating women and the potential differences in characteristics according to partner participation status, and (3) representativity of the women at baseline. Research design and methods We identified women with GDM during pregnancy and invited them and their partners to a baseline examination 10-14 weeks after delivery. Representativity was assessed by comparing the baseline participants with non-participating women, the general population of women with GDM delivering in Denmark, and populations from other intervention trials. Results The penetration rate was 38.0% (867/2279) and the participation rate was 32.9% (285/867). The 285 women who attended baseline had a mean age of 32.7 (±4.8) years and body mass index (BMI) of 28.1 (±5.4) kg/m 2, and 69.8% had a partner who participated. The women participating with a partner were more often primiparous, born in Denmark (82.8% vs 68.2%), were younger, and more often had a BMI ≤24.9 kg/m 2 (35.7% vs 21.2%) compared with women without a partner. Compared with the general population of women with GDM in Denmark, these women broadly had similar degree of heterogeneity, but had higher rates of primiparity and singleton deliveries, and lower rates of preterm delivery and prepregnancy obesity. Conclusions The penetration and participation rates were acceptable. We found a high rate of partner participation. Overall, women participating with a partner were comparable with those participating without a partner. Participating women were broadly similar to the general national GDM population, however with prepregnancy obesity, multiparity, preterm delivery, and multiple pregnancy being less represented. Trial registration number NCT03997773.