PHILADELPHIA -- Fertility treatments can increase multiple births and, in doing so, impose long-range costs in schooling and income on the resulting children, according to researchers at the University of Pennsylvania.
On average, twins weigh 28 ounces less at birth than children born singly, and, according to Penn researchers, this translates into a 12 percent reduction in lifetime earnings for twins compared to singletons.
Penn economics professors Jere Behrman and Mark Rosenzweig are the first researchers to document the causal link between birth weights and lifetime earnings. Their report, "The Returns to Increasing Body Weight," concludes that there are "real payoffs" to interventions that help pregnant women increase their babies' weight at birth.
In 1994 and 1995, the researchers collected data on female twins from the Minnesota Twins Registry, the largest birth-certificate-based twins registry in the U.S. It contains birth records of all twins born in Minnesota between 1936 and 1955. Their empirical research focused on 404 pairs of genetically identical female twins, studying their birth weight, schooling attainment, adult height and adult earnings.
Behrman and Rosenzweig found that twins have considerably lower average birth weight (5 pounds, 10 ounces) compared to the general population (7 pounds, 6 ounces). Also, almost half of twins are low birth weight by the standard definition of low birth weight (below 5 pounds and 8 ounces.)
According to Behrman, when potential parents undergo fertility treatments that could result in multiple births, they undertake a double risk. "Not only do they take the chance of having more children than they bargained for but of having children with less satisfactory education and economic prospects than would result from a singleton birth," Behrman said.
Increasing birth weight increases adult schooling attainment, adult height and adult earnings. Augmenting a chi
Contact: Jacquie Posey
University of Pennsylvania