eli5: how come only some babies get fetal alcohol syndrome from mother’s alcohol consumption during pregnancy?


also how come some heavy drinking mothers give birth to perfectly healthy babies?

In: 24

It depends on the stage of fetal development the mother drinks. I forgot which months are the critical period of fetal development, but if the mother consumes alcohol heavily during that period the likelihood of FAS goes up.

Like many conditions it is multi-factorial.

Part of it is the alcohol drinking, including things like:
– how much
– when in pregnancy – the fetas can be affected at any stage in pregnancy, but the way it is affected varies
– the pattern of drinking (eg regular vs binging

You then have other factors that will interact with the alcohol drinking to impact on the affect on the fetus, like:
– mum’s general health
– mum’s age
– stress levels (steady throughout pregnancy, or a period of high stress, or intermittent periods of high stress)
– nutritional status of mum before and during pregnancy
– medication mum is on
– mum smoking
– mum taking illicit drugs
– genetic variations in mum or the fetus

There will be other factors that haven’t yet been recognised

You then, on top of that, have to look at if the figures for FAS are accurate. Although it is called Fetal Alcohol Syndrome, it is a spectrum. Fetal Alcohol Spectrum or Fetal Alcohol Spectrum Disorders are terms that get used as they highlight the variability.
You get the severe end of the condition where there are structural abnormalities like congenital heart disease or cleft lip/palate. But you can get much milder issues only. If this early on is jut poor growth, and no one knows that mum drank, then the cause might go unrecognised. Likewise if the only features are mild, such as attention. Issues or coordination problems, again it can go undiagnosed. Therefore it’s possible, if not likely, that many go undiagnosed.

Finally those you can get misdiagnosis, and the child that is thought to have FAS actually has another condition that has similar features. There are loads of these. Some will be more easily recognised due to history (there are some drugs for epilepsy that can cause issues which look like FAS. Also if mum has phenylketonuria the infant can be affected). Others are genetic and rare, and technology/availability of that technology is increasing so it makes diagnosing these other conditions easier. Indeed part of the diagnosis of FAS should include some of these tests as screening to rule them in or out. But these are just examples to show that other things can be mistaken for FAS.

Very few things are as simple as “This happened, and here is the consequence,” especially in health. Instead, think of it as going to a roulette wheel at a casino. Unlike the roulette wheel, this wheel has fewer numbers on it. Also, unlike a roulette wheel, you don’t want it to land on your number. So maybe Russian roulette? I don’t own any 5 year olds and so I don’t know if this example goes over their head.

Anyways, the more a mother drinks, the more opportunities for that ball to land on her number, or the bullet lands in her head. Some mothers spin many times. Some mothers spin only a few times. Some mothers walk away (or get by) without ever getting unlucky. But every spin is dangerous.

So, I have traces of fasd because my mother drank whilst pregnant with me, but she also did illicit drugs.

But the drugs were worse.

Don’t take a chance.