Weight gain


After explaining (complaining?) to husband that really, this *huge* baby bump is all amniotic fluid, giant placenta, and fat baby head, he called me on my brash claims and asked to see some data (such a good scientist!).

So I tracked some down.  How much of your weight gain every week is actually due to things like the placenta?  Or anything actually derived from the fetus itself, for that matter?

It took a while, but via a 2009 National Research Council-commissioned report on re-evaluating the recommendations for weight gain during pregnancy in the US, I found an ideal - but data sourceless - figure in a 1976 publication in Clinical Obstetrics and Gynecology.  This figure plots the relative contribution of fetal components (the baby itself, placenta, amniotic fluid) and maternal components (extracellular fluids [i.e., water weight], fat, extra uterine and breast tissue, and extra blood volume) by week of pregnancy.  Since the original image in the 1976 paper was poorly reproduced at best, I used datathief to recreate the figure in R - and I even added a second version with the Y-axis in pounds (right) for any metrically-challenged readers out there.  (You might have to click on the figure to actually read it well - too bad blogspot doesn't let you upload pdf images, 'cause it looked awesome coming out of R.)

Relative contribution of fetal (solid lines) and maternal components (dashed lines) to overall weight gain by week.

The author gives no comment as to where he’s actually getting these numbers, and quite frankly, I’m not sure how one would accurately measure/estimate some of the maternal traits anyway.  I guess it wouldn’t surprise me if there was a way to precisely and non-invasively estimate uterine weight or total blood volume in a living person - in diving sea snakes, I’ve heard of it done by cutting off their heads and draining the blood out into a bucket, clearly not an option here - but even getting pre-pregnancy values must be pretty difficult, given that there are so many unplanned pregnancies in the US, let alone real repeated measures every week.  Europe might be a far better place to conduct such a study.

But in any case, this is what we currently have to work with.  Verdict?  At week 18, the vast majority of my total weight gain is all maternal components - largely lots of blood, a suped-up uterus, and giant boobs - and these maternal factors will relatively outweigh fetal components for the duration of the pregnancy.  No more blaming it on the baby-derived tissue!

Comments

  1. LesleyJuly 10, 2013 at 9:46 PM

    Personally, I think most of the actual bump is your tortured, bloated guts being pushed up and forward... at least at first.

    Another cool science fact is that your brain shrinks by 10% during pregnancy, specifically the grey matter of your cortex! Yup-- I wish I had time to dig up the study for you right now, but if you search the literature for stuff like 'brain mass changes and pregnancy', you might turn up the scary graphs of shrinking brain size and the even scarier photos of before and after brain scans. Not to worry-- it rebuilds itself to normal size by the time the baby is 6 months old.

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