ABSTRACT
Introduction The onset of rhythmic contractions of the primitive embryonic heart between 21 and 24 days after conception initiates an important sequence in the functional development of the embryonic cardiovascular system. The normal development of the embryonic cardiovascular system and the fetoplacental unit are necessary to ensure adequate blood flow, oxygen delivery, and gas and nutrient exchange at organ and cellular levels. As the placenta is the major respiratory organ in utero, the normal maturation of these two circulatory systems is important for adequate fetal growth and development. The first trimester is a period of rapid development in many organ systems coupled with exponential embryonic growth. Thereafter, fetal growth and development continue toward term in a more steady fashion. The cardiovascular system has to match these needs of the growing and developing embryo. It is therefore not surprising that there are important changes in fetal cardiac function that take place in the first and second trimesters.
