Intervention fidelity and behaviour change mechanisms in a health promotion intervention for women following gestational diabetes mellitus: Secondary analysis of the Face-it RCT.

AIMS: We evaluated the fidelity of the Face-it intervention and its impact on behaviour change mechanisms among women with recent gestational diabetes mellitus (GDM).

METHODS

In this randomised controlled trial, 277 women were allocated to usual care or an intervention comprising three home visits, digital platform health coaching and cross-sectoral communication to support health behaviour change during the first year after delivery. Behaviour change mechanisms included social support, motivation, self-efficacy, risk perception and health literacy. High fidelity was defined as completing three home visits and ≥ 9 coaching contacts.

RESULTS

Within the intervention group, 86.4 % completed ≥ 2 home visits, 88.6 % registered digitally with a median (IQR) of 10.0 (3.0-20.0) contacts. At one-year after delivery, the high-fidelity group (n = 73; 39.7 %) had higher odds of perceiving moderate/high diabetes risk (OR 2.42; 95 % CI 1.06-5.51) and higher health literacy (adjusted difference 0.20; 95 % CI 0.04-0.35), whereas no difference was found for social support, motivation and self-efficacy compared with usual care. No difference was observed between the low fidelity and the usual care group in behaviour change mechanisms.

CONCLUSIONS

The Face-it intervention achieved acceptable fidelity. High fidelity appears essential for improving risk perception, health literacy and supporting behaviour change mechanisms among women with recent GDM.