Pregnancy represents a time of rapid bodily change, which includes physical proportions, physiology and responsibility. At this context, maternal vitamin D stores have been the objective of extensive scientific research during the last decades, focusing on their potential effects on maternal an neonatal health. A growing body of observational studies indicated that maternal hypovitaminosis D (as defined by maternal 25-hydroxyvitamin D [25(OH)D] levels <20 ng/ml or <50 nmol/l) is a significant risk factor for adverse neonatal outcomes including asthma, multiple sclerosis and other neurological disorders. On that basis, this review aims to provide to the reader new insights into the vitamin D requirements and function during pregnancy supported by recent data and will not discuss the classical roles of vitamin D and skeletal function during pregnancy. In addition, we will focus on recent results that demonstrate that maternal vitamin D supplementation could reduce neonatal respiratory and neurological complications, suggesting that available guidelines should be updated, since it remains unclear why these recommendations are not updated according to recent results. Also, with regard to randomized controlled trials (RCT's) for vitamin D, we consider that they are largely doomed to fail. The reasons for this are many and specific cases of this failure will be presented in this text.