Physiologic transition from intrauterine to extrauterine life
- Caraciolo J Fernandes, MD
Caraciolo J Fernandes, MD
- Associate Professor of Pediatrics
- Baylor College of Medicine
The successful transition from intrauterine to extrauterine life is dependent upon significant physiologic changes that occur at birth. In almost all infants, these changes are successfully completed at delivery without requiring any special assistance. However, about 10 percent of infants will need some intervention, and less than 1 percent will require extensive resuscitative measures at birth .
The physiologic changes that occur in the transition from intrauterine to extrauterine life are reviewed here. The indications and principles of neonatal resuscitation are discussed separately. (See "Neonatal resuscitation in the delivery room".)
Prior to delivery, the human fetus depends upon the placenta for gas and nutrient exchange with the maternal circulation. A discussion on the development of the placenta, which is essential for normal fetal growth and development, is found separately. (See "Placental development and physiology".)
The low vascular resistance of the placenta and the high vascular resistance of the fluid-filled fetal lungs result in right-to-left shunts characteristic of the fetal circulation (figure 1).
Fetal circulation — In the fetus, the placenta has the lowest vascular resistance and receives 40 percent of the fetal cardiac output, which results in a low systemic pressure (figure 1). In contrast, the fetal lungs are filled with fluid, resulting in a high vascular resistance and less than 10 percent of the cardiac output going to the lungs (algorithm 1). In contrast to earlier studies in lambs, subsequent studies using magnetic resonance imaging (MRI) and Doppler ultrasound to measure fetal blood flow suggest pulmonary blood flow may be higher (11 to 15 percent of combined ventricular output) [2,3].
- Wyckoff MH, Aziz K, Escobedo MB, et al. Part 13: Neonatal Resuscitation: 2015 American Heart Association Guidelines Update for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2015; 132:S543.
- Mielke G, Benda N. Cardiac output and central distribution of blood flow in the human fetus. Circulation 2001; 103:1662.
- Prsa M, Sun L, van Amerom J, et al. Reference ranges of blood flow in the major vessels of the normal human fetal circulation at term by phase-contrast magnetic resonance imaging. Circ Cardiovasc Imaging 2014; 7:663.
- Soothill PW, Nicolaides KH, Rodeck CH, Gamsu H. Blood gases and acid-base status of the human second-trimester fetus. Obstet Gynecol 1986; 68:173.
- Goldsmith JP. Delivery room resuscitation of the newborn. In: Neonatal-Perinatal Medicine: Diseases of the Fetus and Infant, 9th ed, Martin RJ, Fanaroff AA, Walsh MC (Eds), Elsevier Mosby, St. Louis 2011. Vol 1, p.449.
- Olver RE, Walters DV, M Wilson S. Developmental regulation of lung liquid transport. Annu Rev Physiol 2004; 66:77.
- Bland RD, Nielson DW. Developmental changes in lung epithelial ion transport and liquid movement. Annu Rev Physiol 1992; 54:373.
- O'Brodovich HM. Immature epithelial Na+ channel expression is one of the pathogenetic mechanisms leading to human neonatal respiratory distress syndrome. Proc Assoc Am Physicians 1996; 108:345.
- Wilson SM, Olver RE, Walters DV. Developmental regulation of lumenal lung fluid and electrolyte transport. Respir Physiol Neurobiol 2007; 159:247.
- Vyas H, Field D, Milner AD, Hopkin IE. Determinants of the first inspiratory volume and functional residual capacity at birth. Pediatr Pulmonol 1986; 2:189.
- van Vonderen JJ, te Pas AB, Kolster-Bijdevaate C, et al. Non-invasive measurements of ductus arteriosus flow directly after birth. Arch Dis Child Fetal Neonatal Ed 2014; 99:F408.
- Noori S, Wlodaver A, Gottipati V, et al. Transitional changes in cardiac and cerebral hemodynamics in term neonates at birth. J Pediatr 2012; 160:943.
- American Academy of Pediatrics. Overview and principles of resuscitation. In: Textbook of Neonatal Resuscitation, 5th ed, Kattwinkel J (Ed), American Academy of Pediatrics, 2006.