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Why boy babies get sicker than girl babies…



One of the things I learned years ago in the intensive care nursery was that the key to a good call night’s sleep was to have mainly girl babies as your patients. It was (and I imagine still is) common wisdom in NICUs everywhere: boys just did worse than girls. Their lungs seemed weaker and their immune systems punier; they got sicker, and quicker, than the girls did. Thinking back, most of the harrowing patients I can recall were boys.

I didn’t spend a whole lot of time wondering or worrying about what seemed to me to be an obvious case of neonatal gender injustice. I figured it was all part of Mother Nature’s grand cosmic scorecard: if boys didn’t have to grow up and have babies, they could stand to suffer a bit more on the front end of life. (A philosopher, as you may have noted from previous posts, I am not…).

Now researchers at the University of Adelaide in Australia have come up with a genetic explanation for this boys-have-it-worse NICU phenomenon. In an article titled (deep breath…) “Integrative transcriptome meta-analysis reveals widespread sex-biased gene expression at the human fetal–maternal interface,” Dr. Claire Roberts, the lead investigator in Adelaide, explains it all:

We obtained gene expression data for .300 non-pathological placenta samples from 11 microarray datasets and applied mapping-based array probe re-annotation and inverse-variance meta-analysis methods which showed that .140 genes (false discovery rate (FDR) ,0.05) are differentially expressed between male and female placentae.  

To which I say: Who didn’t already know that?

In a closer approximation to spoken English, Dr. Roberts continues:

There is strong evidence that human males and females differ in terms of growth and development in utero and that these divergent growth strategies appear to place males at increased risk when in sub-optimal conditions.

Which means: Boy + Prematurity = Bad News.

The reason for the poorer outcomes in boys seems to be related to gender differences in how certain genes are expressed during pregnancy. In females these differences–and there are about 140 of them known to date–mean that there is more emphasis on placental development, the maintenance of pregnancy, and maternal immune tolerance. According to Dr. Roberts, girl babies are more “risk-averse” toward development and survival in utero than boys, which translates into better neonatal outcomes. Meanwhile, the gene expression differences  in boys mainly just make them get bigger than girls.

So if I understand this correctly, girl fetuses are smaller and smarter about survival than boy fetuses, and the boys are bigger and “less risk averse” than the girls. Sounds a lot like high school.

In fairness, the study is written for molecular biologists, who no doubt gobble this “inverse-variance meta-analysis” sort of thing right up. For those on the NICU front lines, though, it confirms the advice once given to me by a senior resident while we awaited a middle-of-the-night premature birth: “Bottom line, Sloan–if you want to sleep tonight, pray it’s a girl.”

Photo by Rosa’s Cakes

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June 1, 2014 · 3:39 pm