|
Robert
Jansen MD The authors - gynaecologists from Sheffield, epidemiologists from Southampton, England - have proposed that there are two groups of women with polycystic ovaries: those who are overweight, and those who have normal weight. This is a condition known as polycystic ovary syndrome in Australia and Europe, and polycystic ovarian disease (PCOD) in the U.S. It's one of the commonest disorders of ovulation to cause infertility ... but it's also estimated that one-in-five women have it to a greater or lesser extent. The normal-weight PCO women might have their condition because their mothers went past 40 weeks before they gave birth. As a theory it's plausible .... just! We know that the human brain is "imprinted" around the time of birth, depending on how the hormonal milieu in the uterus is affecting the fetus. Creswell (the gynecologist), Barker (the epidemiologist) and their colleagues obtained data on 968 pregnancies that resulted in a female baby being born alive in Sheffield between 1952 and 1953. 235 still lived in Sheffield, agreed to be interviewed, and had ultrasound scans done of the ovaries. 49 of the 235 women had polycystic ovaries - over 20% of the women. This is about the percentage we would expect: remember that PCO is so common that it's doubtful we should call it "abnormal". Creswell and Barker found that the longer the duration of the pregnancy - that is, the more the pregnancy went past 40 weeks (called "postmaturity") - the greater the chance that PCO would later develop (but only the normal-weight type of PCO). From this the authors speculate that the postmaturity caused lower estrogen levels at the end of the pregnancy - and higher androgen (male hormone) levels. These androgens then imprint the developing hypothalamus to produce too much luteinizing hormone, which is the essence of the disturbance in PCO. Plausible ... yes. But remember that Creswell and Barker were not testing this hypothesis. They had a completely different hypothesis in mind (that small size at birth would cause PCO). (This hypothesis was not supported.) Their finding was unpredicted -- and they devised their theory after the fact. This does not necessarily affect the truth of the association between one observation (pregnancy going post-term) and the other observation (thin women with PCO). The next step, however, will be to see if the same relationship also holds true in other groups of women. But coming up with the theory or hypothesis after the fact does weaken the idea that one causes the other. Keeping in mind that we already know that it is the fetus rather than the pregnant woman who determines when labor will begin, there's a second and a third logically valid conclusion that Creswell and Barker could have drawn. The second is that PCO is genetic and that there's something about PCO in fetuses already destined to have PCO that makes them go post-term (i.e. PCO-tendencies cause postmaturity). A VARIATION ON THIS THEME IS IN FACT A HIGHLY PLAUSIBLE ALTERNATIVE EXPLANATION: THAT THE CHILDREN WITH PCOS WERE MORE LIKELY TO HAVE MOTHERS WHO HAD PCO - AND WHO WOULD HAVE HAD LONG CYCLES AND LATE OVULATIONS, MAKING IT SEEM LIKE THE CHILDREN WERE BORN POST-TERM. The
third is that something else (something unknown -- perhaps a low
nutrition state in the uterus) causes both PCO and postmaturity. But the explanation that PCO mothers have long cycles and late ovulations, and thus have pregnancies that in the 1950s would have seemed post-term without a detailed menstrual history being available, is so plausible, and so ignored by the authors of the paper, that we should be sceptical about this study. So it's too early to conclude that inducing labor at 40 weeks will prevent lots of cases of PCO, See the article's abstract at the National Library of Medicine. For
more on PCOS, see WebPages 2 and 11 on the main site. Order the U.S. version of Overcoming Infertility from Amazon Books or Barnes and Noble. Last updated : Feb 2003
|
Introduction ~ The
Book ~ The Author ~ Glossary
Reviews ~ Order
~ Sydney IVF ~
Going Deep ~ Email
Us
©2003 Robert Jansen