Yes, the effects of several supplements on gestational diabetes have been examined, including vitamin D,[1][2] polyphenols,[3] probiotics,[1][4][5] myo-inositol,[1][6] fish oil (including omega-3 fatty acids),[1], etc. Of these, supplementation with vitamin D or myo-inositol during pregnancy may reduce the risk of gestational diabetes [1]. But there is currently no strong evidence to support the use of supplements to treat gestational diabetes.