Introduction: Maternal nutrition is critical to the health of both mother and offspring. Intakes of micronutrients such as iodine, calcium, iron, folate and vitamin D play an important role in preventing adverse pregnancy and birth outcomes, however there is a paucity of data on the nutritional adequacy of diets during pregnancy. Objectives: Our objective was to identify to what extent pregnancy reduces the nutritional adequacy of the expecting mother’s diet and if this nutritional gap can be resolved by simple quantitative or qualitative changes in the diet. Method / Design: Using a comprehensive probabilistic approach, the PANDiet scoring system, we evaluated the observed nutritional adequacy of diets of French and American women of childbearing age (n=344 and n=563) participating in ENNS and NHANES and we simulated the changes in adequacy in all nutrients and the final overall PANDiet scores of women of childbearing age who would remain on their diet during pregnancy. Then, by either increasing the quantity of consumed foods or using snacks recommended during pregnancy, we simulated the effect of a 150-kcal increase in the energy intake of French women of childbearing age. Results: Simulation of pregnancy in women of childbearing age lowered the probabilities of adequacy for the intake of some nutrients (8 out of 34 in France including folate, vitamin D and iodine, and 9 out of 30 in the US including folate), resulting in a decrease in the overall PANDiet score, which was similar in both countries. Simulated 150-kcal increases in energy intake, with an increase in the quantity of food consumed or using recommended snacks only partially corrected this decrease. Indeed, those snacks failed to address the decrease in adequacy related to some of critical micronutrients during pregnancy. Conclusions: Pregnancy induces an important nutritional gap, which is not efficiently addressed with simple generic dietary advice.