News
Old lessons, growing relevance
More than 3 decades ago, the late British physician Dr. David Barker got us thinking about how a challenging life in the womb can set us up for downstream ill health. He studied births from 1910 to 1945 and found that the cardiovascular mortality of individuals born during that time was inversely related to birthweight. Smaller babies, he found, could have cardiovascular mortality risks that were double or even quadruple the risks of larger babies.
Dr. Barker theorized that, when faced with undernutrition, the fetus adapts by sending more blood to the brain and sacrificing blood flow to less essential tissues. His theory about how growth and nutrition before birth may affect the heart became known as the "Barker Hypothesis." It was initially controversial, but it led to an explosion of research – especially since 2000 – on various downstream effects of the intrauterine environment.
Investigators have learned that it is not only cardiovascular mortality that is affected by low birthweight, but also the risk of developing diabetes and being overweight. This is because the fetus makes less essential systems insulin resistant. Insulin resistance persists in the womb and after birth as well, predisposing individuals to insulin resistance and obesity, both of which are closely linked to the risk of metabolic syndrome – a group of risk factors that raises the likelihood of developing heart disease, stroke, and diabetes.
In fact, further research on cohorts of Barker children – individuals who had low birthweights – has shown that not only have they had higher rates of cardiovascular disease, but they have had higher blood sugars and higher rates of insulin resistance as well.
Today, we appreciate a fuller picture of the Barker data, one that shows a reversal of this trend when birthweights reach 4,000-4,500 grams. At this point, what was a progressively downward slope of cardiovascular mortality rates with increasing birthweight suddenly shoots upward again when birthweight exceeds 4,000 g.
It is this end of the curve that is most relevant – and most concerning – for ob.gyns. today. Our problem in the United States is not so much one of starving or growth-restricted newborns, as these babies account for 5% or less of all births. It is one of overweight and obese newborns who now represent as many as 1 in 7 births. Just like the Barker babies who were growth restricted, these newborns have high insulin levels and increased risk of cardiovascular disease as adults.