I advise having this as a snack instead of just drinking alongside food due to the carbs in the smoothie.
You could also add double cream and/or nuts/seeds and avocado.
Avoid using higher sugar fruits such as banana, mango, pineapple, passionfruit etc as higher GI fruits will not be tolerated as well.
I do not advocate using protein powders as part of the GD diet. Try to stick to REAL FOOD. The research around the use of protein supplements in pregnancy suggests that they can cause lower birth weights in babies and whilst many may think this ideal with gestational diabetes, it is not. Many women with gestational diabetes see a complication of slowed growth, small for gestational age and IUGR babies and so this is not something we would want to risk. The diet I advocate is high in protein from natural protein sources and so I do not advocate adding additional protein supplements such as protein powders.