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U.S. babies getting smaller?

By Mary Renee Reuter

Babies have often been considered a bundle of joy, but that bundle may be getting smaller in the United States.

Babies have often been considered a bundle of joy, but that bundle may be getting smaller in the United States.

A recent Harvard study found that the average birth weight of U.S. babies declined in the last 15 years after steadily increasing since 1950. All the infants in the study were full-term and non-multiples.

While the 2-ounce decline was small, a continuation of this trend could be troubling. Small-for-gestational-age infants often require longer hospital stays in order to put on more weight. Very small babies have difficulty regulating their body temperature and may experience respiratory distress syndrome. As a result, such infants are placed in incubators to control the temperature and oxygen levels in their environment.

University of Hawai`i Professor Lynn Yamashita, who specializes in infant development, notes that the change is not significant enough to pose an immediate health threat to the majority of infants, but the study is surprising.

“This study is a big puzzle,” Yamashita said. “The [results] go against what you would think, people are getting heavier and yet, the infants are smaller.”
Yamashita stressed that the lower birth weights indicated in the study are not the same as low birth weight or preterm infants with a high risk for health problems.

“It might actually be that women with gestational diabetes are getting better prenatal care and are able to manage their diet better, and that’s a good thing,” Yamashita suggested. The Harvard study indicated a decrease in the birth weight of large-for-gestational-age infants. Infants over 10 pounds can also be a health risk to both the mother and the infant.

The researchers behind the study, published in the February edition of Obstetrics and Gynecology, did not explain the cause behind the decline. However, several factors are known to lead to lower birth weights, including absent or inadequate prenatal care, poor nutrition, stress, smoking, anemia, diabetes, short intervals between pregnancies, and poor weight gain.

According to Robert S. Feldman’s “Development Across the Life Span,” the rate of low birth weight infants differs among racial groups. Feldman says this is not due to the actual race of the mother, but due to the fact that members of racial minorities have disproportionately lower incomes, which can affect the mother’s stress, her access to medical care, and adequate nutrition. The percentage of low-birth weight infants born to African American mothers is double that of Caucasian American mothers.

However, in this particular study, the decline in birth weight could not be attributed to racial disparities or many of the common known causes. In fact, the decline was even more dramatic among the demographic subgroup with the lowest risk for low birth weight infants. There was a 79-gram decline in infant birth weights among married non-smoking Caucasian mothers with access to education and prenatal care versus a 52-gram decline among the over all population.

Officials with the Women, Infants & Children nutrition program, also known as WIC, hope to help decrease the number of low birth weight and premature infants by offering nutritional services including education and supplying free approved foods to pregnant and breast feeding mothers, as well as children under five.
Lyn C.N. Salamanca, M.S. R.D., is the Nutrition Services and Support Coordination with Hawaii’s Department of Health’s WIC branch. She suggests another reason for birth weight decline.

“Women who are overweight or obese prior to their pregnancy do not necessarily have heavier babies,” Salamanca said. “A woman who is already obese prior to pregnancy might have poorer nutrition, diabetes, hyperglycemia or other health issues.” Such medical conditions can make it necessary to induce labor earlier, which can lead to a lower birth weight for the infant.

Salamanca’s explanation could suit the Harvard study, especially after researchers exhausted any of the expected explanations.
Yamashita added, “I think with this latest study what really stands out is that researchers are saying there is something here going on that we haven’t yet started to question.”