Dietary Assessment in Pregnancy
All pregnant women should undergo individualized dietary assessment focusing on pre-pregnancy BMI, current eating patterns, weight gain trajectory, and specific micronutrient intake, with particular attention to folic acid, iron, and vitamin D status, followed by targeted supplementation and counseling based on identified deficiencies. 1, 2
Essential Components of Dietary Assessment
Pre-Pregnancy and Current Nutritional Status
Assess pre-pregnancy BMI to establish appropriate weight gain targets: underweight women (BMI <19.8) should gain up to 18 kg total, normal-weight women should gain 1.4-2.3 kg in the first trimester and 0.5-0.9 kg/week thereafter, overweight women should gain at less than 50% of normal-weight rates, and obese women (BMI >30) should limit total gain to 5.0-9.1 kg. 2, 3
Evaluate current dietary patterns using food frequency questionnaires or 24-hour dietary recalls to identify intake of nutrient-dense whole foods (fruits, vegetables, legumes, whole grains, nuts, seeds, fish, lean protein) versus highly processed foods. 4
Screen for dietary restrictions that may compromise nutritional adequacy, particularly ketogenic diets (lacking carbohydrates), Paleo diets (restricting dairy), or diets with excess saturated fats, all of which should be avoided during pregnancy. 4
Micronutrient Intake Assessment
Critical deficiencies to screen for:
Folic acid status: All women require 400 µg/day from fortified foods and/or supplements starting before conception through at least the first trimester; women with obesity or diabetes require 5 mg/day. 1, 2, 5
Iron intake: Average dietary intake often falls short of requirements; assess for risk factors requiring 30 mg/day supplementation during second and third trimesters. 6, 2
Vitamin D status: This is commonly deficient and requires specific assessment, as dietary intake alone rarely meets requirements. 7
Zinc intake: Average intake is 11 mg/day while RDA is 15 mg/day; assess particularly in women with low pre-pregnancy weight and low plasma zinc levels, as supplementation leads to higher infant birth weight. 6, 2
Calcium adequacy: Generally supplied by balanced diet, but assess intake patterns to identify specific needs. 1
Macronutrient and Energy Assessment
Energy requirements by trimester:
- First trimester: No additional calories needed unless woman begins pregnancy with depleted body reserves. 1, 2, 3
- Second and third trimesters: Additional 300 kcal/day required to support maternal blood volume expansion, breast and uterine growth, placental development, fetal growth, and amniotic fluid. 6, 2, 3
Protein requirements:
- Standard recommendation: 0.75 g/kg/day plus an additional 10 g/day during pregnancy. 6, 2, 3
- Updated evidence: More recent data suggest 1.2 g/kg/day during early pregnancy (
16 weeks) and 1.52 g/kg/day during late pregnancy (36 weeks). 2
Monitoring Tools and Red Flags
Implement systematic monitoring:
- Daily food records to track actual intake patterns and identify under-eating. 6
- Weekly weight checks to ensure appropriate weight gain trajectory by trimester. 6, 2
- Ketone testing to detect inadequate caloric intake, as ketonemia has been associated with lower intelligence scores in offspring at ages 2-5 years. 6, 2
Critical pitfall: Never allow or recommend hypocaloric diets below 1,200 calories/day, as they result in ketonemia and ketonuria with documented adverse neurodevelopmental outcomes in offspring. 6, 2
Dietary Restrictions to Assess and Counsel
Absolute avoidances:
- Alcohol: Complete avoidance required, as no amount is considered safe during pregnancy. 1, 2, 3
- Vitamin A in retinol form: Avoid during first 12 weeks due to teratogenic risk; beta-carotene form is safe and preferred. 1, 3
- Raw animal products and soft cheeses: Avoid to prevent foodborne illness. 2
- Caffeine: Limit to no more than 200 mg per day. 2, 3
Nonnutritive sweeteners: FDA-approved sweeteners (saccharin, aspartame, acesulfame-K, sucralose) appear safe for use during pregnancy in moderation. 6, 2
Special Population Considerations
Women post-bariatric surgery:
- Require nutritional screening every trimester including ferritin, folate, vitamin B12, calcium, vitamin D, and vitamin A levels. 1, 2
- Vitamin B12 levels should be monitored every trimester with supplementation adjusted to maintain normal serum concentrations. 1, 2
Women with diabetes:
- Require higher folic acid dose (5 mg/day). 1, 3
- Benefit from carbohydrate distribution throughout the day into three small-to-moderate meals and 2-4 snacks, with an evening snack usually necessary to decrease overnight hypoglycemia and fasting ketosis. 2
- May benefit from modest energy reduction (33% calorie restriction or 1,600-1,800 kcal/day) if obese, which reduces mean blood glucose without elevations in plasma free fatty acids or ketonuria, whereas more severe restriction (50% calorie restriction) increases ketonuria. 6
Practical Assessment Algorithm
First trimester visit:
- Document pre-pregnancy BMI and establish weight gain targets. 2, 3
- Initiate or verify folic acid supplementation (400 µg/day standard, 5 mg/day if obese or diabetic). 1, 3
- Assess dietary pattern quality and counsel on nutrient-dense whole foods. 4
- Screen for dietary restrictions and avoidances. 1, 3
Second and third trimester visits:
- Monitor weight gain trajectory weekly. 6, 2
- Initiate iron supplementation (30 mg/day). 2, 3
- Reassess dietary intake if weight gain is inadequate or excessive. 2
- Consider zinc supplementation if indicated by low pre-pregnancy weight or low plasma zinc. 2
- Perform ketone testing if under-eating is suspected. 6, 2
Throughout pregnancy:
- Emphasize that most patients can absorb oral folic acid even with malabsorption of food folates. 5
- Recognize that food is the optimal vehicle for nutrient intake, but prenatal vitamin and mineral supplements are often prescribed due to uncertainty of nutritional status and intake. 6
- Adjust supplementation based on individual assessment rather than universal protocols. 1, 2