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Can someone explain why a single dose of hCG causes a LH surge?

Discussion in 'Step I' started by auburnO5, Apr 3, 2012.

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  1. auburnO5

    auburnO5 5+ Year Member

    Dec 15, 2008
    I understand that it's made early by the embryo and then syncytiotrophoblasts to keep the corpus luteum producing progesterone.

    I guess I can't figure out why it would cause an LH surge.

    This is in the setting of an anovulatory/infertile female seeking fertility treatment, after doses of menotropins (GnRH?) were given.
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  3. lakerfan38

    lakerfan38 7+ Year Member

    May 26, 2009
    hCG is very similar to LH.

    Same alpha subunit as LH and similar beta subuint

  4. lookmanohands


    Mar 25, 2012
    (here's what I think/remember): The infertile woman is probably lacking FSH and LH. The menotropins are probably acting like FSH to handle what FSH was supposed to do.

    FSH, LH, TSH, and hCG share a common alpha subunit so hCG can simulate an LH surge if you spike it into her. I think it's actually replacing the LH surge, not causing an LH surge
  5. medstud87

    medstud87 2+ Year Member

    Mar 6, 2011
    ^This. Basically hCG = LH w/ weak FSH and TSH (TSH can cross placenta--> maternal hyperthyroidism but unapparent because of estrogen increasing TBG). Produced by placenta in order to 'save' the corpus luteum --> production of estrogen/PROGESTERONE from ovaries and corpus luteum until 2nd trimester when placenta takes over. Is actually highest in concentration 2nd and 3rd trimester.

    Key board style question I got from Kaplan... "When can ovaries be removed during pregnancy (I don't know why you'd want to remove them but whatever)?"
    Ans: After 1st trimester because placenta takes over.

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