A reader fisked the concluding statement in my previous post by email:
Although your post about infant mortality is spot on, there really isn’t much evidence that prenatal care has a major impact on preterm delivery, especially in black women. The only intervention that I’m aware of for which there’s RCT data is the use of progesterone in women with a history of prior preterm labor, and even that is a bit shaky (I’m actually working on a CEA of that right now, and when you drill down on the published data it’s not nearly as convincing). Prenatal care is undoubtedly a good thing, and there is evidence that it does improve some outcomes (although, especially in the US, we do too much of it), but, sadly, the one thing it doesn’t seem to do is prevent preterm delivery.
To which I replied: “Fair enough. You bring up good points, and I’m sure I let my emotions get the better of me there. But there has to be a reason for the preterm labor. Do you think it’s genetic? Or is it lifestyle choices – which I’d argue could be impacted and reduced by better care. No?”
His answer was very complete and chock full of evidence, so I’m posting it in its entirety (with his permission):
Personally, I think there is some genetic component–at every gestational age, black babies are smaller than babies of other ethnicities (the distribution is still normal, but it’s shifted to lower weights–that’s why any discussion of racial disparities in low birthweight needs to adjust for this), but, at any gestational age, their survival is better (a black baby born at 31 weeks has better survival than a white baby, but, because there are more 31 week deliveries, overall mortality is higher in blacks), and there are differences in the distribution of pelvic shapes (black women are more likely to have a narrower pelvic outlet. There’s been a lot of speculation about differences in responses to infection/inflammation, uterine physiology (black women are much more likely to get fibroids, for example), or generalized vascular reactivity. From an evolutionary perspective, there may have been some advantage to having smaller babies at earlier gestational ages. But I’m not aware of a lot of active research into this.
The disparity exists even when you control for other factors–for example, there’ve been a series of studies in active duty military women, who all have access to the same care, have similar incomes, etc, and the disparity is still there (e.g., http://www.ncbi.nlm.nih.gov/pubmed/16477258). There’s a lot of interest in looking at disparities in environmental exposures (http://www.ncbi.nlm.nih.gov/pubmed/18828412) and some discussion about the effects of racism/social deprivation on stress (although I’m somewhat skeptical about that). Black women tend to have shorter interpregnancy intervals, which are associated with preterm birth, but I’m not sure that’s causative. But all of these things are bigger social/public health issues and, by the time someone’s in prenatal care, it’s probably too late. Sure, smoking cessation probably helps (although, again, very little direct evidence of an effect on birth outcomes–we did an RCT of NRT here and found no difference in birth outcomes despite higher quit rates), but that doesn’t explain very much of the black/white disparity.
Here’s the Cochrane review on increased support for women at high risk for preterm birth: http://www.ncbi.nlm.nih.gov/pubmed/20556746 and here’s the one for number of prenatal visits http://www.ncbi.nlm.nih.gov/pubmed/20927721 (there is an impact on perinatal mortality, but it’s in settings with an already low number of visits, where perinatal mortality is common, and where the causes of perinatal mortality are less likely to be prematurity).
I admit it’s hugely frustrating, because that excess infant mortality is by far the biggest driver of disparities in life expectancy. Some of the other causes are potentially impacted by lifestyle choices that could be impacted by care and/or other strategies (for example, there’s a big difference in MVA-attributable infant mortality between blacks and whites, which is probably due to differences in car seat/seat belt use, and we have some preliminary data… which suggests that MVA-attributable stillbirth is more common in blacks, again because of less frequent seat belt use. We can address that, but it’s not nearly as big a contributor as prematurity). But it seems likely that a lot of it is due to some combination of genes and environment that can’t be easily dealt with at the health care “system” level, and until we find a better primary prevention strategy, we’re stuck with few options besides short term tocolysis and antepartum corticosteroids.
None of this lessens the fact that infant mortality in the US is still too high, compared to other countries. But my final assertion that better access to good prenatal care would solve this problem seems like an unsubstantiated claim. I still think it does a lot of good for many things, but this reader may be right that it won’t do much to prevent the deaths due to prematurity.
P.S. This reader’s comment and follow-up is a phenomenal example of how you should go about getting us to pay attention and change our minds.