Birthweight and infant mortality inequality

Birthweight drives the Black-White gap.

Here’s a look at birthweight patterns and their effects on the difference in infant mortality rates between Black and White children.

A new report from the Centers for Disease Control, based on 2007 data, shows the distribution of birthweights and mortality outcomes by the race/ethnicity of mothers. Here is a story in three figures.

1. The infant mortality rate gap is large

In the figures below I focus on White (non-Hispanic), Black (non-Hispanic), and Hispanic. Since White and Hispanic infants have such similar rates, the issue I’m most concerned with is the Black-White gap.

2. Infant mortality rates are drastically affected by birthweight. But at each birthweight the race/ethnic gap is small.

The Black mortality rates are higher among the high-birthweight infants, but there are very few deaths out there (note the log scale, which is necessary to even see those gaps).

3. Black mothers are much more likely to have very-lowbirthweight infants.

Again, because of the log scale, you can see the gaps clearly even though there are very few births at the very low end. Still, 1.8% of Black women’s infants are born below 1,000 grams, where a large portion of infants don’t survive.

So what explains the higher infant mortality rates among Black women’s infants? The overwhelming issue is birthweight. If they had the same mortality rates at each birthweight, I calculate, the gap would close by 10%. But if they had the same birthweight distributions, the gap would close by 88%.

In previous posts, I reported that women who experienced childhood hardships are more likely to have low-birthweight babies. And I described the weathering hypothesis, which suggests delaying first births only improves outcomes for infants if their mothers’ health is not already deteriorating in their 20s, as it more often is with Black women. With this evidence, it is clear that the major problem driving the infant-mortality gap is not care of newborn infants itself, but rather the long-term health of Black women.

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