The study of more than 11,000 UK mums also found those with a history of eating disorders, like anorexia and bulimia, are more than twice as likely to need fertility treatment to help them conceive.
The study by King's College London and University College London found pregnancy rates after six months were lower in the women who suffered from eating disorders, but after a year they were in line with the general population.
Over thirty nine per cent of women with a history of bulimia or anorexia took longer than six months to conceive, but surprisingly, these women had more unplanned pregnancies than those who have never suffered an eating disorder.
'This research highlights that there are risks to fertility associated with eating disorders,' said Lead researcher Dr Abigail Easter.
'However, the high rates of unplanned pregnancies in women with a history of anorexia suggest that women may be underestimating their chances of conceiving.
'Women planning a pregnancy should ideally seek treatment for their eating disorder symptoms prior to conception, and health professionals should be aware of eating disorders when assessing fertility and providing treatment for this.'