Breathing: Fetal Breathing

R. Harding, S. B. Hooper, C. A. Albuquerque

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Fetal breathing movements (FBMs) are breathing-like movements that occur episodically in healthy mammalian fetuses. As with postnatal breathing, FBMs are centrally organized rhythmic contractions of the diaphragm, but may also involve other skeletal muscles such as those of the chest wall and upper respiratory tract. Owing to the airways being filled with liquid, FBMs cause only minor changes in lung volume but typically lower intrathoracic pressure by up to 5 . mmHg and alter the shape of the fetal chest. By altering intrathoracic pressure they affect blood flow within the fetus and fluid movement within the fluid-filled fetal airways. FBMs are characteristically highly variable in frequency and amplitude, but become more organized with increasing gestational age and relate to fetal behavioral states. They are inhibited by fetal hypoxia and hence can be used in the diagnosis of fetal compromise. FBMs are critical for normal in utero lung growth and development as they maintain the fetal lung in an expanded state by opposing lung recoil: in the absence of FBMs the fetal lungs tend to 'deflate' leading to lung hypoplasia. At birth, breathing becomes continuous, possibly by removal of inhibitory substances produced by the placenta or fetal brain and by increased carbon dioxide production.

Original languageEnglish
Title of host publicationEncyclopedia of Respiratory Medicine, Four-Volume Set
PublisherAcademic Press
Number of pages5
ISBN (Print)9780123708793
Publication statusPublished - 1 Jan 2006


  • Development
  • Diaphragm
  • Fetal assessment
  • Fetus
  • Lung
  • Lung hypoplasia
  • Lung liquid

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