March 08, 2007

Fat Chance

From Reuters: Go On, Embrace The Mental Image
WASHINGTON (Reuters) - Obese couples have a more difficult time conceiving a baby than couples of normal weight, according to a study published on Tuesday . . .

Previous research had established that semen quality and levels of reproductive hormones were diminished in overweight men.
Talk about demeaning research subjects: "Hey, fatty, jerk off in this cup!"

The new study, in fact, seems entirely to lack a point other than demeaning the overweight. Notes the article:
The study did not examine whether heavier couples had sex less frequently than normal weight pairs.

"If, for example, the obese couples hardly ever had sex then, of course, the chances of becoming pregnant would be reduced. But we don't know that at all," [lead researcher Cecilia] Ramlau-Hansen added.
Okay, so let me get this straight, you conducted a 'study' on links between pregnancy and obesity without tracking how many times couples actually had sex? Do you have low quality semen for brains or are you just extremely naive? How can we possibly draw any valid conclusions about fertility in the overweight, especially considering, DURRRR, previous research has shown that obese individuals DO have sex less. Have you heard of a literature review, Dr Ramlau-Hansen?

So, basically, this article is saying: we got nothing, but lose some weight or no babies for you. It's a fairly brazen piece of anti-obesity propaganda. Now, I think previous blog entries of mine have made it clear that I'm a member of the anti-obesity camp myself, but considering there are so many good reasons not to be obese, I don't see how making up sensationalist ones is going to help anybody.

I think early in the morning before my brain has really kicked in is a terrible time to be writing about such an inflammatory topic. How many people have I offended?


Anonymous said...

Andrew you are quick to judge. The main problem with your rant is that you've pulled all you information from that watered down Reuter's article. That leads to hillariously naive writing that you can tear to shreds. Unfortunately the actual study isn't as stupid as you would have us believe. Here's the article's abstract.


BACKGROUND: Recent studies indicate that not only women's but also men's obesity has adverse effects on fecundity and since fecundity is a couple concept, we examined fecundity in relation to overweight and obesity of the couple. We also examined the association between weight changes and fecundity over time.

METHODS: Between 1996 and 2002, 64 167 pregnant women enrolled in the Danish National Birth Cohort were interviewed during and 18 months after pregnancy. Information on body mass index (BMI) and waiting time to pregnancy (TTP) was available for 47 835 couples.

RESULTS: Among men and women with a BMI of 18.5 kg/m–2 or more, we found a dose-response relationship between increasing BMI group and subfecundity (a TTP of more than 12 months): Odds ratio (OR) = 1.32 (95% CI: 1.26–1.37) for women and OR = 1.19 (95% CI: 1.14–1.24) for men. Among 2374 women with an initial BMI of 18.5 kg/m–2 or more, who participated more than once in the Danish National Birth Cohort, each kilogram increment in weight between the two pregnancies was associated with a 2.84 (95% CI: 1.33–4.35) days longer TTP.

CONCLUSIONS: Couples have a high risk of being subfecund if they are both obese.

Key words: fecundity/fertility/obesity/overweight


This is an oportunistic finding from an enormous cohort. This isn't a study about obsesity and pregnancy at all. The survey deisgners could probably only get a couple questions related to obesity in there. Too many questions just overwhelms participants and they give up.

As far as I cant tell this is a perfectly good finding from a much larger sample than you'd normally have access to. Not only that, they've been upfront about the strenghts and weakneses of their design. Not bad for people with low quality semen for brains.

Now, why you wouldn't want to know the frequency of sex in a larger study about pregnancy rates is another question all together.

Kevin Casey

Andrew said...

Yeah, I'm quick to judge. I thought that was part of my irreplicable charm.

I thank you for presenting the abstract, but I think, as I understand it, my original objection still stands. The study is looking at how the time it takes for a couple to conceive varies with BMI; frequency of sex will (inescapably and by design) affect how long it takes for a couple to conceive; the study did not control for frequency of sex. I therefore have a hard time seeing how these results are meaningful, because it seems like they would be greatly altered by the inclusion of frequency of sex in the regression model. If I'm missing something obvious please explain it to me.

Also, from what little I can recall from my murky memories of stats class, Odds Ratio results are notoriously hard to interpret. What this says is that people with a higher BMI are between 1.2 and 1.3 times more likely to take over twelve months to conceive (more likely than what I'm not quite clear -- I imagine people with a low BMI). But this doesn't tell us what the actual odds for either group are, and it is possible that even though the analysis is statistically significant, it is not practically significant. (Let's say the odds of subfecundity for a normal couple are 1 in 4; this study would suggest that for an obese couple the odds would be increased to 1 in 3.1-ish. Is that a 'big' difference? By what criteria?)

So, sorry to be dismissive, but I still don't buy it. It's great that they have such a large cohort to analyse and admirable that they'll admit their weaknesses -- but simply admitting that you made a huge mistake doesn't make it any less of a mistake in statistical terms.

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