Anorexia nervosa is characterised by refusal to maintain a healthy body weight, and an obsessive fear of gaining weight due to a distorted self image. The results may be driven by a mistaken belief among women with anorexia that they can't get pregnant because they either don't have menstrual periods or have irregular periods, the journal Obstetrics & Gynaecology quoted Cynthia M. Bulik, who led the study, as saying.

"Anorexia is not a good contraceptive," said Bulik, director of University of North Carolina's eating disorders programme in the US. "Just because you're not menstruating, or because you're menstruating irregularly, doesn't mean you're not at risk for becoming pregnant," he added, according to a university statement.

Bulik and study co-authors analysed data collected from 62,060 women as part of the Norwegian Mother and Child Cohort Study. There were 62 women in this sample who reported having anorexia nervosa.

The differences between women with anorexia and those with no eating disorder were striking.  The average age of the mothers at delivery was 26.2 years in women with anorexia, compared with 29.9 years in the group of women without eating disorders.

Fifty percent of women with anorexia reported unplanned pregnancies, compared with 18.9 percent of the others, while 24.2 percent of women with anorexia reported having induced abortions in the past, compared to 14.6 percent of the others.