title: Effect of rising hCG levels on the human corpus luteum during early pregnancy.
abstract: BACKGROUND
  During early pregnancy, the most important task of the corpus luteum (CL) is to produce sufficient progesterone until the luteoplacental shift occurs. Progesterone production is closely related to the extensive vasculature surrounding and supplying the CL. The synthesis of both progesterone and factors controlling the vasculature in the CL is regulated by hCG, which is released initially at rising levels from the placenta. The primary aim of this research was to evaluate changes in the CL vasculature during early pregnancy.
  
  
  METHODS
  Twenty naturally conceived pregnancies were examined weekly from weeks 5 to 11. At each visit, blood samples were obtained to determine the concentrations of hCG, progesterone and 17-OH progesterone (17-OHP). The vasculature in the ovaries was assessed using three-dimensional power Doppler ultrasonography.
  
  
  RESULTS
  The vascular supply in the ovary containing the CL was greatest at week 5, and thereafter, declined continuously until week 11. The decrease in the vasculature correlated with the decrease in 17-OHP. Mean hCG levels reached a maximum at week 8, progesterone levels reached the nadir at week 7 and increased after that.
  
  
  CONCLUSIONS
  Vasculature in the CL appears to be created already by the fifth week of pregnancy and it does not enlarge despite rising hCG levels. The activity of the CL during pregnancy may be measured non-invasively by assessing its vasculature with three-dimensional ultrasonography.
authors.affiliation: Department of Obstetrics and Gynecology, Oulu University Hospital, Oulu, Finland. ilkka.jarvela@oulu.fi
authors.forename: Ilkka Y
authors.initials: IY
authors.lastname: Järvelä
authors.forename: Aimo
authors.initials: A
authors.lastname: Ruokonen
authors.forename: Aydin
authors.initials: A
authors.lastname: Tekay
mesh_terms: D019326:17-alpha-Hydroxyprogesterone / Q000097:blood; D000328:Adult; D006063:Chorionic Gonadotropin / Q000502:physiology*; D003338:Corpus Luteum / Q000098:blood supply*; D005260:Female; D006801:Humans; D010053:Ovary / Q000098:blood supply / Q000000981:diagnostic imaging; D011247:Pregnancy; D011261:Pregnancy Trimester, First / Q000502:physiology*; D011266:Pregnancy-Associated Plasma Protein-A / Q000378:metabolism; D011374:Progesterone / Q000097:blood; D014463:Ultrasonography
chemical_list: D006063:Chorionic Gonadotropin; D011374:Progesterone; D019326:17-alpha-Hydroxyprogesterone; D011266:Pregnancy-Associated Plasma Protein-A