A pound of flesh may be worth a lot more than you think.
Low birth weight can cause a number of health risks during infancy and beyond, said New York University Sociology Professor Dalton Conley, who presented his research on the subject Friday at the Colonial Penn Center.
Conley pointed out a high correlation between low birth weight and infant mortality. Babies weighing more than 2,500 grams -- approximately 5.5 pounds -- have a 0.35 percent mortality rate in their first year, he said, while the rate for those weighing between 1,500 and 2,500 grams at birth is 2.2 percent. Thirty percent of infants born weighing less than 1,500 grams die before reaching the age of 1.
Low birth weight babies who survive also have other risks later in life. As proof of this, Conley discussed studies showing that children with low birth weight are 50 percent less likely to graduate high school in a timely fashion than their siblings who were heavier at birth.
But, he added, it is necessary to examine whether increased mortality rates for babies with low birth weight are actually caused by weight and not by some other factor. According to Conley, low birth weight can be accompanied by other risk factors such as low parental income, poor maternal health during pregnancy or genetic problems.
As a result, it can be difficult to extract the true causes of these infant deaths.
To tackle this problem, Conley looked at the effects of birth weight on infant mortality rates in twins. By studying fraternal twins with different birth weights, he hoped to factor out the effects of many other possible causes. Both twins would be exposed to the same environment in terms of maternal health and parental socioeconomic status.
Conley found that an infant with low birth weight was more likely to die before age 1 than his fraternal twin weighing more than 5.5 pounds. But since fraternal twins do not share the exact same genes -- they are only as genetically similar as two non-twin siblings -- Conley felt that the difference he observed could still be attributed to genetic problems in the twin with low birth weight.
To rule out this possibility, Conley also studied identical twins. If the higher mortality rates are caused by genetics and not birth weight itself, the identical twins of low birth weight babies should also be at higher risk.
But even in identical twins, Conley found that a birth weight of less than 5.5 pounds was correlated with a higher incidence of infant death, despite the fact that both babies share the exact same genes.
Thus, Conley concluded that low birth weight, not just genetics or environmental factors, can lead to a higher chance of infant mortality.
"Fetal growth does matter," he said.
