title: Changes in the size of maternal inferior vena cava during pregnancy.
abstract: OBJECTIVE
  To investigate the changes in the size of maternal inferior vena cava (IVC) during normal pregnancy.
  
  
  METHODS
  The diameter and the area of IVC were measured in 32 non-pregnant and 214 pregnant women by ultrasonography. They were measured not only in the supine but also in the complete left lateral position when gestation was over 16 weeks.
  
  
  RESULTS
  IVC in the 4-7 weeks pregnant group was larger than that in the non-pregnant group, and it decreased as gestation progressed during an early stage of pregnancy. After 16 weeks gestation, it demonstrated no change, at least for depending on the periods when the mother was in the supine position. On the contrary, they increased with the gestational progress as for the maternal left lateral position.
  
  
  CONCLUSIONS
  The size of IVC at an early stage of pregnancy is enlarged, suggesting an underfilling state of arterial circulation. In the second and third trimesters, it is stationary when the mother is supine. In the left lateral position, it increases as the gestation progresses, reflecting blood volume expansion during pregnancy.
authors.affiliation: Department of Obstetrics and Gynecology, Musashino Red Cross Hospital, Tokyo, Japan. yonchi@med.teikyo-u.ac.jp
authors.forename: Eiji
authors.initials: E
authors.lastname: Ryo
authors.forename: Nobuya
authors.initials: N
authors.lastname: Unno
authors.forename: Tsuneki
authors.initials: T
authors.lastname: Nagasaka
authors.forename: Yuji
authors.initials: Y
authors.lastname: Taketani
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy / Q000502:physiology*; D011264:Pregnancy Trimesters / Q000502:physiology; D012016:Reference Values; D016216:Ultrasonography, Prenatal; D014682:Vena Cava, Inferior / Q000000981:diagnostic imaging / Q000502:physiology*