During pregnancy, mothers-to-be should adapt their diet to meet increases in nutrient requirements. Pregnant women appear to be keener to adopt healthier diets, but not always successful. The objective of this study was to determine whether a guided, stepwise and tailored dietary counseling program, designed using an optimization algorithm, could improve the nutrient adequacy of the diet of pregnant women, beyond generic guidelines. 80 pregnant women who attended Notre-Dame-de-Bon-Secours Maternity Clinic were randomly allocated to the control or intervention arms. Dietary data were obtained twice from an online 3-day dietary record. The nutrient adequacy of the diet was calculated using the PANDiet score, a 100-point diet quality index adapted to the specific nutrient requirements for pregnancy. Women were supplied with generic dietary guidelines in a reference booklet. In the intervention arm, they also received nine sets of tailored dietary advice identified by an optimization algorithm as best improving their PANDiet score. 78 pregnant women completed the 12-week dietary follow-up. Initial PANDiet scores were similar in the control and intervention arms (60.4±7.3 vs 60.3±7.3, P=0.92). The PANDiet score increased in the intervention arm (+3.6±9.3, P=0.02) but not in the control arm (-0.3±7.3, P=0.77), and these changes differed between arms (P=0.04). In the intervention arm, there were improvements in the probabilities of adequacy for ALA, thiamin, folate and cholesterol intakes (P<0.05). Tailored dietary counseling using a computer-based algorithm is more effective than generic dietary counseling alone in improving the nutrient adequacy of the diet of French women in mid-pregnancy.