The Dec. 2015 Home Birth Study & Understanding Risk

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by

mentorchar
in

Many of you have seen the NYT article about the new home birth study. And, if you were a brave soul, you read through the comments, wherein a large number of people did the predictable anti-home birth flailing, this time carrying a red flag reading “This shows babies are 250% more likely to die! Make it illegal! Selfish mothers!”

Except that’s not what the math shows, at all.

First of all, lets look at the numbers the article gives- for hospital births, 1.8 deaths per 1000. For home births, 3.9 per 1000.

Now we look at what is called “Relative Risk”: The number that tells you how much something you do, such as having a home birth, can change your risk compared to your risk if you have a hospital birth. Relative risk can be expressed as a percentage decrease or a percentage increase. If something you do doesn’t change your risk, then the relative risk reduction is 0% (no difference). If something you do lowers your risk by 30% compared to someone who doesn’t take the same step, then that action reduces your relative risk by 30%. If something you do triples your risk, then your relative risk increases 300%.

3.9/1000 is a roughly 117% relative increase from 1.8/1000. Not 250%. (a 217% relative increase would be 5.9)

That means the actual relative risk is 117%.

That still sounds like a scary number, right? If you have a home birth there’s a 117% greater chance of infant death, oh no!.

Except now we look at “Absolute Risk”: The number of percentage points your own risk changes if you do an action.

1.8/1000 is .18% and 3.9/1000 is .39%, that means that there were .18% deaths in hospitals, and .39% deaths at home.  the absolute increase is .21%.    Put in layman’s terms:

The absolute increased risk of infant death in home vs hospital shown by this study is less than 1/4 of 1%. The risk of infant death in both cases is less than 1%

No matter where you give birth, there is a less than 1% chance your baby will die- and the risk in a home birth is a whopping .21% higher than in a hospital.  Not as scary as the detractors would have you believe.