The recent discovery of a Polynesian-specific gene variant with links to metabolic function shows promise as a potential drug target for treating metabolic disorders. The missense variant, termed R458Q, of the CREBRF (CREB3 regulatory factor) gene, has been associated with an increase in body mass index and yet, almost paradoxically, protection against type-2 diabetes. This gene variant has also been shown to be protective against the development of gestational diabetes mellitus (GDM) althought the mechanisms underlying this effect are yet to be elucidated. It has been shown in rodents that the hormones prolactin and its homologue, placental lactogen, play a key role in driving maternal adaptations of glucose regulation, and dysfunction of these adaptations can contribute to the development of GDM. Here, we aimed to use a mouse model with a ‘knock in’ of the R458Q gene variant of CREBRF to investigate if this gene variant leads to increased secretion of these pregnancy hormones conferring a ‘gain-of-function’ protective mechanism. First, we characterised prolactin secretion patterns in early pregnancy in control and R457Q CREBRF gene knocked-in (KI) mice fed either a standard diet or a high fat diet. Tail tip blood samples were collected at 8 time points over a 24 hour period in early pregnancy and prolactin was measured using a highly sensitive enzyme-linked immunosorbent assay (ELISA). A terminal blood sample was collected in late pregnancy (day 16) to measure total lactogenic activity using a live cell bioassay. In early pregnancy, KI mice have significantly higher prolactin levels compared to wildtype mice, in both the HFD-fed and control diet fed groups (2-way ANOVA, Effect of genotype P=0.0178, n=5-7 per group). These results support the hypothesis that enhanced prolactin secretion during pregnancy could contribute to the protective effect of this CREBRF gene variant in the development of gestational diabetes.