Pre-pregnancy belly means big baby

Women who have large waistlines before pregnancy may be more likely to have a larger-than-normal newborn, a new study suggests.

The findings, reported online in BJOG, are in line with what experts know: women who are obese before pregnancy are more likely to have a baby with macrosomia.

Depending on how macrosomia is defined, it affects anywhere from 1% to 10% of pregnancies. By one definition, babies born weighing more than 4 kg are macrosomic. Another definition puts the threshold at 4.5 kg.

In the new study, UK researchers found that women with the biggest pre-pregnancy waistlines were more likely to have a macrosomic newborn, whatever the definition.

Of nearly 3,100 women who gave birth over one year, about 10% had a baby weighing more than 4 kg, while about 1% had a newborn that weighed more than 4.5 kg.

Body fat distribution important

Women who fell in the top 25% for pre-pregnancy waist-to-hip ratio were 57% more likely to have a baby weighing more than 4 kg than women in the bottom 25% for waist-to-hip ratio. They were also 2.6 times more likely to have a newborn weighing more than 4.5 kg, after adjustment for pre-pregnancy body mass index (BMI).

We know that total body fat is associated with pregnancy outcome, senior researcher Dr Gordon C.S. Smith told Reuters Health in an email. This study suggests that the distribution of the body fat may also be important.

That fits with what's known about visceral fat and other types of health problems, said Dr Smith, who heads obstetrics and gynaecology at Cambridge University.

Right now, experts use BMI as the basis for weight-gain recommendations to pregnant women. But if further studies point to the importance of waist size, Dr Smith said, weight-gain recommendations during pregnancy may need to become more sophisticated.

(Reuters Health, November 2011) 

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