Major studies decades ago revealed variability of menstrual cycles

But people are still naïve about the basic cause of the difficulty to achieve pregnancy

Sex education at school, its quality or otherwise, is likely to have much to do with fertility problems later in life. Many women (men, too, of course) can use the  keyboard with all their fingers (as well as their thumbs!) but have poor understanding of the basic functioning of their reproductive system.

colonial classroom


That ignorance is well known, and is underlying the fertility problems. You should see the pregnancy doctors’ tweets – replying to some incredible questions, and then the talk of various mysteries!

A shining example is this tale of “mysterious conception”. For the whole story see the Alphabet of bioZhena under M, “Mysterious conceptions (OR THE NONEXISTENCE THEREOF)” on page 34 or thereabout, from which I cite:

QUOTE:  It appears that we must dwell on this topic, because of stories and notions propagated in various pertinent circles. This writing has been prompted by page 176 in the excellent 1999 book “Woman” by Nathalie Angier, where the Pulitzer laureate relates the story of the mysterious conception of her only child. Mysterious, because it occurred, she believes and makes her readers believe, outside of ovulation and of the fertile window.

The reason for this entry in the Alphabet of bioZhena is that there is NO SUCH THING AS MYSTERIOUS CONCEPTIONS, there is only lack of information, or ignorance of the facts. We might say, intellectual misconceptions lead to “mysteries” in terms of conception, of babies conceived supposedly when conception was biologically impossible, and vice versa, some women have difficulties conceiving for the same fundamental reason. We shall use Ms. Angier’s case to make this point. UNQUOTE.

To drive the point home, here is an excerpt from John J. McCarthy, Jr. and H.E. Rockette, “Prediction of ovulation with basal body temperature”, Journal of Reproductive Medicine, Volume 31 (No.8), Supplement, 742 – 747, 1986.

Referencing particularly large studies from 1967 and 1977, these BBT experts had this to say all those years ago (and never mind their “prediction” in the cited title whereas the BBT is well known to be no predictor):

QUOTE:  Cycle regularity is often assumed by both women and their physicians. The suggestion, that the BBT graph of the previous cycle can be used to identify the day of ovulation in the current cycle, requires nearly absolute cycle regularity. [However, note this:] The data collected by 1,085 women, who provided at least 6 or more charts each, were studied for cycle length variability. … The cycle length range was more than five days for 56% of the women who submitted 6 graphs, and for 75% of those with 12 graphs. … Absolute regularity was not demonstrated in as few as six cycles. Even when the cycle length that deviated the most was eliminated, less than 1% (8 of 1,085 women) had no variation in cycle length. When the number of cycles was extended to 12, no woman had variability of less than two days in cycle length. END OF QUOTE.

In real life, you realize, no cycle can be eliminated from the experience, and every day matters. Two days are very likely to make the difference between conception and the lack of it. And/or cause an unwanted pregnancy, for that matter.


Middendorf  – On the ball

The above findings are therefore the basis on which we can say quite categorically that nobody is as regular as a metronome (and nobody conceives in an anovulatory cycle), that there is no such thing as absolute regularity, whether 28 days or otherwise.

If you are in the sub-fertile category of people finding it difficult to become pregnant, you are likely to have cycle variability of more than 5 days over those months of your fruitless efforts that define your category. More likely than being one of the 0.74% of the population with no variation in cycle length, which under ideal conditions may also mean no variation in the time of ovulation. Persistent monitoring is well advised.


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3 Responses to “Major studies decades ago revealed variability of menstrual cycles”

  1. The fallacy of ovulation calculators, calendars and circulating-hormone detectors « bioZhena’s Weblog Says:

    […] flawed assumption of similar timing of menstrual cyclic events from one cycle to another has been a problem for the BBT and the BBT thermometers. Since the late sixties, the microprocessor […]

  2. Why too many young and not so young ladies could NOT receive flowers on Mothers’ Day: Why so many trying-to-conceive, why so much infertility « bioZhena's Weblog Says:

    […] example of such a post is “Major studies decades ago revealed variability of menstrual cycles” (But people are still naïve about the basic cause of the difficulty to achieve […]

  3. End of the year, and trying to get pregnant « bioZhena's Weblog Says:

    […] from one cycle to the next. Check out this earlier bioZhena post for evidence that this is so. See evidence generated by other experts years or rather decades ago – when they hoped that microcomputer-assisted basal body […]

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