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Menstrual Cycle

Discussion in 'MCAT Study Question Q&A' started by supertrooper66, Jun 14, 2008.

  1. supertrooper66

    supertrooper66 Banned

    Apr 28, 2008
    ok there's this TBR CBT question that discusses how variable the 28-day menstrual cycle is. one question says if a woman's cycle is 20-24 days, her expected period of ovulation is expected to be _____ days. well, normally it's on day 14. SO, with a 28-day normal cycle, you would assume it occurs half way through the cycle (14/28). So, I chose 10-12 days because that would be the midpoint range for a 20-24 cycle. It said I was wrong and that the answer is 7-9. the answer explanation says assuming the luteal phase is fairly constant in all individuals, you subtract 14 from the 22 day average of 20-24 giving you 7-9. HOWEVER, no where in the passage does it say the luteal phase is consistently 14-days across all women. ONLY in the answer does it make that assumption, an unfounded assumption. how would the test taker know to make that assumption? they wouldn't. they would do what i did and get it wrong.

    is this simply a poorly written question since it is from a practice test company?
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  3. bluemonkey

    bluemonkey 7+ Year Member

    Oct 2, 2007
    I don't want to make a judgement about the quality of the question, but this seems rather complicated for the MCAT. While it is true that the luteal phase is FAIRLY consistent among women, it can actually exhibit variation, ranging from 9-16 days. That said, a given woman will have a consistent length in her luteal phase. So if this woman's cycle were 24 days, then ovulation could take place anywhere from 6 days to 13 days (22-16 or 22-9; we use 22 because menstruation is days 23 & 24). If the cycle were 20 days, then you would expect lower numbers. It seems that the question or passage must provide the stipulation of a constant luteal phase (which is not necessarily true) in order for you to arrive at the credited answer choice.
  4. rox

    rox ossified 7+ Year Member

    Jul 9, 2006
    Far away
    "Ovulation occurs 14 days before menses, regardless of cycle length" - BRS Physiology.

    This is a fact.
  5. bluemonkey

    bluemonkey 7+ Year Member

    Oct 2, 2007
    Hmm...I pulled my info from my physio text. It does indeed say that most luteal phases are 14 days in length, however, there can be some variation. I wonder why the discrepancy?
  6. pluckyduck1105

    pluckyduck1105 7+ Year Member

    Mar 6, 2008
    As with all biological phenomena, there is always some range of variability and sometimes even exceptions to so-called rules. Onset of menstruation can be affected by numerous variables such as a woman's diet, changes in weight/body composition, stress, medications, physical activity, and even being around other women by way of pheromones. It is even possible for a woman to ovulate during a cycle but skip menstruation completely, as the two are separate things (this is called amenstruation). However, the general rule of thumb is that menstruation begins 14 days after ovulation. I don't really know if this would be absolutely necessary knowledge for the MCAT, my books didn't really stress the 14 day thing, I only know about it from my women's health class last semester after my teacher told us and pretty much made us memorize it bc it was going to be on the test. Whatever, now you know and it'll definitely be something good to know when you do become a doctor. Periods are kind of a big deal for us girls.
  7. unsung

    unsung 10+ Year Member

    Mar 12, 2007
    This is a a fact that's come up in EK too, I've noticed. Basically, what's key to remember is that time til ovulation varies in different women. But luteal phase is *exactly* 14 days in all women 'cuz it's genetically determined. (Whereas follicular phase/ovulatory phase depend on a complex interplay of different hormone levels.)

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