Bigger mothers = bigger newborns

Increasing body-mass index (BMI) of mothers accounts for most of the rising incidence of macrosomia in newborns, researchers from China report in an issue of BJOG.

The incidence of large-for-gestational-age or macrosomia (birthweight of 4000 g or more) infants has been rising in most developed countries over the past 2 decades, and several studies have examined the risk factors responsible for the increase.

Dr Yashuang Zhao and colleagues from Harbin Medical University, Harbin, Heilongjiang Province, examined trends in the incidence of foetal macrosomia in Harbin, China between 2001 and 2005 and sought to identify factors responsible for the trends.

Among a total of 13,711 births, 1373 newborns (10.01%) had macrosomia and 207 (1.51%) had birth weights of at least 4500 g.

The incidence of macrosomia increased from 8.31% in 2001 to 10.50% in 2005, whereas the incidence of birth weight of at least 4500 g increased from 1.38% in 2001 to 1.89% in 2005.

Concerns raised

These increases raise concerns, the investigators say, because "macrosomia is associated with increased risks of shoulder dystocia, brachial plexus injury, skeletal injuries, and perinatal mortality. Adverse long-term effects of foetal macrosomia may include the subsequent development of obesity and possibly malignancies."

In a multivariate model, prepartal BMI of at least 30 kg/meter squared, prepartal BMI between 25 and 29.9 kg/meter squared, maternal height of at least 165 cm, gestational age between 40 and 41.9 weeks, maternal age of 30 years or older, and measured hypertension were significantly associated with an increased risk of macrosomia.

These trends were all significantly associated with the rising trend in macrosomia.

Obesity biggest contributor

"The factor with the greatest contribution to this increase was the increase in obesity, as measured using BMI," the authors say.

"The significant increase with time in the incidence of macrosomia is consistent with earlier reports for Chinese immigrants in Australia and Yantai, and for the general population in Germany," the researchers add, but the results contrast with those of a recent study reporting decreases in birth weight and in the incidence of large-for-gestational-age births for term, singleton neonates in the USA from 1999 to 2005.

"Our findings underline the importance of the maintenance of normal weight in women of childbearing age, the appropriate weight gain in pregnant women, and, more generally, health education," they conclude.

(Reuters Health, December 2010)

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