by Colette Bouchez
Girls who weigh very little when born appear to catch up to their peers later in life. Boys, however, do not.
That's the finding of experts who followed 195 very low birth weight, premature babies from their first year of life through age 20.
"We always knew that very low birth weight babies were smaller in the first year of their life, but no one ever followed them for an extended time period to see if they caught up -- or when they caught up -- and in this study we were able to do that by following them to age 20," says study author Dr. Maureen Hack, a pediatrician at Rainbow Babies and Children's Hospital in Cleveland. The report, from researchers there and at Case Western Reserve University, appears in the July issue of Pediatrics.
A baby is considered premature if born before the 37th week of pregnancy. A baby is considered at low birth weight if the infant weights less than 2,500 grams, or 5.5 pounds. Very low birth weight babies weigh 1,500 grams to about 3 pounds, sometimes less.
The fact that the girls grew faster in the first year of life was not a surprise, Hack says, because premature girls generally are healthier and stronger after birth than premature boys.
However, something of a surprise came 20 years later.
"Male babies born prematurely with very low birth weight have more severe disease and more problems during the first year of life so growth was always slower than girls -- but we assumed that at least some would catch up," Hack says. "But none did."
The researchers also discovered most of the girls' "catch-up" growth came between ages 8 and 20 -- a spurt, says Hack, that could result in health problems later in life.
"There is some research to show that accelerated growth during childhood can be a predictor of type 2 diabetes and cardiovascular disease later in life, so there is some concern for these girls," she says.
For pediatrician Dr. David Horwitz, the study offers interesting statistical data, but he says it's not enough information to predict future health risks.
"From a purely epidemiological point of view, it's extremely fascinating information -- and it's very important to have this data for the future," says Horwitz, a clinical associate professor of pediatrics at the New York University School of Medicine.
However, he says, it will be 30, 40 or more years before doctors know the clinical significance of what the study found.
"It's not until this group of children is well into their 50s and 60s and we see the rate of disease that we will know if their low birth weight or their rapid growth periods did, in fact, put them at any greater risk for disease," Horwitz says.
To suggest this connection now, he says, is a leap of faith.
The study followed 195 premature babies -- 103 boys and 92 girls -- born between 1977 and 1979. Each baby reached an average gestational age of 29.8 weeks and weighed an average of 1,189 grams (less than 2 pounds) at birth.
At the same time, researchers put together a database of 208 babies of normal birth weight born during the same time period -- 101 boys and 107 girls -- to serve as the control group.
Weight and height measurements were taken on all the children at birth, 40 weeks, 8 months and 20 months, and then again at 8 years and 20 years of age. In addition, body mass index (BMI), a measurement of body fat, also was taken at ages 8 and 20.
Researchers then compared the height, weight and BMI statistics of the boys to the girls, as well as the very low birth weight group to the normal birth weight children.
The result: Among the babies born with very low birth weight, the girls outpaced the boys in growth rate during the first year, but still remained small for their size compared with the normal birth weight babies. However, between ages 8 and 20, all the very low birth weight girls caught up to their peers, even to the point of sharing similar rates of obesity.
The boys, however, remained small in height and weight and never caught up to their peers in the normal birth weight group.