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Babies' birth weights falling

January 25, 2010

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Newborn babies are getting smaller, even when they are full term, a Boston study finds, reversing a 50-year trend linked to mothers’ higher weight and lower smoking rates.

The surprising results, reported by Dr. Emily Oken and a team from Harvard, Harvard Pilgrim Health Care, and Boston University, come from an analysis of almost 37 million birth records in the United States from 1990 through 2005. Over the 16 years, birth weights for single babies born from 37 to 41 weeks’ gestation fell by almost 2 ounces. Weights fell almost 3 ounces among babies whose mothers were white, well educated, married, didn’t smoke, had prenatal care early in their pregnancies, and didn’t have cesarean sections - all factors correlated with healthy-weight babies.

The trend was not explained by mothers having labor induced or delivering by C-section, nor by the length of pregnancy, which has dropped by more than two days since 1990. Overall, the proportion of babies considered large for their gestational age declined slightly while the proportion considered small ticked upward. These changes were greater among low-risk mothers.

The reasons for the weight declines are unclear, but the researchers suggest that the modest change may represent a reversal of previous increases. Because very low birth weight can cause serious problems for babies at birth and throughout their lives, the researchers urged more study.

BOTTOM LINE: After decades of steady increases in birth weight, full-term babies weighed almost 2 ounces less in 2005 than in 1990.

CAUTIONS: The study relied on estimates of gestational age, which can be unreliable.

WHERE TO FIND IT: Obstetrics & Gynecology, February

New therapy shows promise against major cause of diarrhea

An experimental therapy to prevent recurrence of an increasingly troublesome bacterial infection that is the leading cause of hospital-acquired diarrhea worked significantly better than standard treatment, Massachusetts researchers report.

Infections caused by the bacterium Clostridium difficile recur in up to one-third of patients, mostly people over 50, after they are treated with antibiotics for the initial infection. Scientists suspect that antibiotics destroy normal organisms in the digestive system, making people more vulnerable to new C. difficile infections or resurgence of the bacteria that persist despite antibiotics.

A team from MassBiologics, which is part of University of Massachusetts Medical School, and the New Jersey biotech company Medarex used genetic engineering to create human antibodies that would fight C. difficile. In a clinical trial led by Dr. Donna Ambrosino, the researchers randomly assigned 200 patients receiving standard antibiotics for C. difficile infections to get either a single infusion of the monoclonal antibodies or a placebo. After 84 days, seven of the 101 patients in the antibodies group had a recurrence, compared with 25 of 99 patients in the placebo group.

BOTTOM LINE: A new therapy that attacks bacteria that can cause debilitating diarrhea reduced second episodes of infection by 72 percent compared with standard treatment.

CAUTIONS: In a small subgroup of patients infected with a virulent strain of the bacterium, the recurrence rates were not significantly different. Also, some of the researchers work for Medarex or have equity interests in Medarex or Merck, which has licensed the product. Ambrosino is one of its inventors, but said she does not stand to gain financially from it.

WHAT’S NEXT: Larger trials will be needed to validate the results.

WHERE TO FIND IT: New England Journal of Medicine, Jan. 21

ELIZABETH COONEY

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