Pregnancy myths debunked

I have seen posts on other blogs and comment boards about this issue. Two pregnancy related fallacies seem to be repeated with unfortunate frequency. I thought I'd take a minute here to debunk both of them, so that if any readers come across them, you'll have the right info.

The first is that one of the reasons that Sarah Palin never looked pregnant was that "Down's babies are small." What's the reality here? It is true that Down's babies do have a slightly lower average birthweight when compared to non-Down's babies. But, it's not all that much, and, in this case, doesn't even appear to apply. Trig Palin weighed 6 lbs 2 oz at birth, at 36 weeks gestation. This is actually a very normal and even a bit above average weight for 36 weeks. Babies gain approximately 1/2 lb a week during the last four weeks of pregnancy. If Trig had gained at that rate, his term birth weight would have been right at 8 lbs. He was "normal for dates" so anyone using this to prove that that's why she wasn't showing much just doesn't have their facts straight.

The second oft-repeated mistake is that because "more Down's babies are born to older mothers, that proves that Trig must be Sarah's." In one place, I read the glib assertion, "There's almost no chance a 17 year old would have a Down's baby." These statements are so wrong in so many ways, I hardly know where to begin, but I'll give it a shot.

Women over 40 have approximately a 1 in 40 chance of giving birth to a baby with Down's. Women under 20 have a 1 in 1600 chance. However, 80% of the Down's babies born in the US are born to women UNDER 35 simply because that age group has so many more babies born to it. Yes, it is more likely that on a given pregnancy a woman over 40 will have a Down's baby as opposed to a younger woman, but "more likely" does not equal "true." It is more likely that you won't win the lottery if you buy a ticket, but that does not mean that it is "true" that you won't win the lottery. People win the lottery every day.

Let me repeat that one more time: 80% of Down's babies in the US are born to women under 35. Knowing that Trig Palin has Down's allows us to draw NO conclusions about who his mother is.