Objective To investigate fertility treatment, twin births, and unplanned pregnancies in pregnant women with eating disorders in a population-based sample. Design A longitudinal population-based birth cohort (Generation R). Setting Rotterdam, the Netherlands. Sample Women from the Generation R study who reported a history of (recent or past) anorexia nervosa (n = 160), bulimia nervosa (n = 265), or both (n = 130), and a history of psychiatric disorders other than eating disorders (n = 1396) were compared with women without psychiatric disorders (n = 4367). Methods Women were compared on the studied outcomes using logistic regression. We performed crude and adjusted analyses (adjusting for relevant confounding factors). Main outcome measures Fertility treatment, twin births, unplanned pregnancies, and women's feelings towards unplanned pregnancies. Results Relative to women without psychiatric disorders, women with bulimia nervosa had increased odds (odds ratio, OR, 2.3; 95% confidence interval, 95% CI, 1.1–5.2) of having undergone fertility treatment. Women with all eating disorders had increased odds of twin births (anorexia nervosa, OR 2.7, 95% CI 1.0–7.7; bulimia nervosa, OR 2.7, 95% CI 1.1–6.6; anorexia and bulimia nervosa, OR 3.795% CI 1.3–10.7). Anorexia nervosa was associated with increased odds of unplanned pregnancies (OR 1.8, 95% CI 1.2–2.6) and mixed feelings about these pregnancies (adjusted OR 5.0, 95% CI 1.7–14.4). Pre-pregnancy body mass index did not explain the observed associations. Conclusions Eating disorders are associated with increased odds of receiving fertility treatment and twin births. Women with anorexia nervosa were more likely to have an unplanned pregnancy and have mixed feelings about the unplanned pregnancy. Fertility treatment specialists should be aware that both active and past eating disorders (both anorexia nervosa and bulimia nervosa) might underlie fertility problems.