This book offers a valuable clinical resource for health professionals and researchers. It gives an overview about the pivotal role played by High Molecular Hyaluronic Acid (HMW-HA) during pregnancy and its applications in the gestational period. Hyaluronic acid is a critical component of the extracellular matrix (ECM) and one of the most interesting, versatile and useful natural molecules in almost all areas of biology. As widely reported, HA has a pivotal role in several phases of pregnancy, from fertilization to labour and it displays several regulatory activities and functional properties based on its different molecular weight. While low molecular weight hyaluronic acid (LMW-HA) is widely used in gynaecology for menopause-related symptoms or in association with physical treatments (e.g., radiation therapy) to counteract the onset of adverse events, HMW-HA has been poorly evaluated as clinical treatment. Its physiological presence in the extracellular matrix of all the main organs and tissues involved in pregnancy (uterus, cervix, placenta, decidua, chorion, amnios, ovarium etc..) suggests the importance of this molecule for a successful gestation. Several papers, in particular, shed light on its importance for blastocyst adhesion and implantation, for an efficient immune tolerance and for the correct development of haemo-lymphatic system. It has been demonstrated that HMW-HA has regulatory activity on the PGRMC1 expression, a specific progesterone receptor expressed in maternal and foetal-maternal interface tissues, involved in uterine quiescence. On these premises, the administration of HMW-HA may represent an interesting treatment opportunity for the prevention of recurrent miscarriage and pre-term birth (PTB) in patients with risk factors. The high safety profile of HMW-HA further supports its administration in pregnancy. All these interesting topics will be discussed and deepened in this book, giving the opportunity to explore in detail every aspect of this effective and attractive molecule, thus helping physicians to assess the state of connective tissues in pregnancy and to evaluate the risk for the onset of gestational complications.