“…Nine articles indicated that the samples were stored at a temperature ranging between −18 °C and −70 °C after serum preparation [ 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 48 ]. In eight studies, samples were collected after an overnight fast [ 36 , 38 , 39 , 41 , 42 , 43 , 44 , 48 ]; whereas in the remaining three studies, the prandial state of participants was not specified [ 40 , 45 , 47 ]. Vitamin content of maternal serum/plasma and colostrum was analysed through high-performance liquid chromatography-UV (HPLC-UV) in eight studies [ 36 , 38 , 39 , 40 , 41 , 42 , 43 , 44 ], one combined HPLC-UV and a protein-binding assay [ 45 ], and one study used UV spectrophotometry [ 47 ].…”