What are the effects of eating at maintenance calories during the 2nd trimester of pregnancy?

Eating at Maintenance Calories During the Second Trimester is Insufficient and Risks Maternal-Fetal Complications

You should consume an additional 300 kcal/day above your pre-pregnancy maintenance intake during the second trimester to support critical maternal and fetal physiological changes. Eating at maintenance calories during this period fails to provide adequate energy for the substantial metabolic demands of pregnancy and may compromise outcomes.

Why Additional Calories Are Essential in the Second Trimester

The second trimester marks a critical transition when energy demands increase substantially to support:

• Maternal blood volume expansion (increases by approximately 40-50% during pregnancy) 1, 2
• Placental growth and development (the placenta reaches functional maturity and increases nutrient transfer) 3
• Fetal growth acceleration (the fetus undergoes rapid tissue development and weight gain) 3, 1
• Uterine and breast tissue expansion (preparing for continued fetal growth and lactation) 3, 4
• Increased protein synthesis (protein synthesis increases by 15% in the second trimester) 3

The American College of Obstetricians and Gynecologists explicitly recommends 300 additional kcal/day during the second and third trimesters, not maintenance-level intake 1, 2, 4.

Consequences of Inadequate Energy Intake

Risk of Ketosis and Neurodevelopmental Harm

Eating at maintenance calories (or below energy needs) can trigger ketonemia and ketonuria, which have been directly associated with lower intelligence scores in offspring at ages 2-5 years 3, 1. This occurs because:

• Insufficient caloric intake forces the body to break down fat stores for energy 3
• Ketone bodies cross the placenta and accumulate in fetal tissues 3
• The developing fetal brain is particularly vulnerable to ketone exposure 1

The guidelines are unequivocal: hypocaloric diets below 1,200 calories/day should never be prescribed during pregnancy, and even modest caloric restriction can produce harmful ketosis 3, 1.

Inadequate Weight Gain and Poor Outcomes

Maintenance-level eating typically results in insufficient gestational weight gain, which is associated with:

• Increased risk of preterm birth 5
• Low birth weight infants 5, 6
• Impaired fetal growth and development 6, 7
• Compromised maternal physiologic adaptations (the body cannot make necessary adjustments for pregnancy) 6

Weight gain should be steady and progressive during the second trimester at 0.5-0.9 kg/week for normal-weight women 3, 1, 4.

Protein and Micronutrient Deficiencies

Energy intake below needs compromises protein utilization because:

• Protein synthesis is energy-dependent at every stage (absorption, transport, synthesis) 3
• Protein requirements increase to 1.2 g/kg/day in early pregnancy and 1.52 g/kg/day in late pregnancy 1, 2
• Without adequate calories, dietary protein gets diverted for energy rather than tissue building 3

Additionally, maintenance eating makes it nearly impossible to meet increased micronutrient needs for iron (30 mg/day), folate (400 µg/day), zinc (15 mg/day), and calcium 3, 1, 2.

The Correct Approach: Calculated Energy Addition

For Normal-Weight Women (BMI 18.5-24.9)

• Add exactly 300 kcal/day to your pre-pregnancy maintenance intake starting in the second trimester 1, 2, 4
• Monitor weight gain weekly to ensure 0.5-0.9 kg/week progression 3, 1
• Total target weight gain: 11.5-16.0 kg across entire pregnancy 4, 8

For Underweight Women (BMI <19.8)

• Add 200 kcal/day in the second trimester (more than normal-weight women) 8
• Target higher weight gain: up to 18 kg total pregnancy 3, 1, 4
• These women have depleted reserves and need additional energy 3, 4

For Overweight Women (BMI 25-29.9)

• Still add 300 kcal/day, but monitor closely 1
• Weight gain should be <50% of normal-weight rates 3
• Target: 6.8-11.3 kg total pregnancy 1, 8

For Obese Women (BMI ≥30)

• Add 450 kcal/day in the second trimester (paradoxically more than normal-weight women in some guidelines) 8
• Alternative recommendation: 100 kcal/day above pre-pregnancy intake has shown successful outcomes in some studies 3
• Target: 5.0-9.1 kg total pregnancy 1, 4, 8
• Never restrict below 1,600-1,800 kcal/day total to avoid ketosis 3

Critical Monitoring to Prevent Under-Eating

To ensure you're not eating at maintenance (which is insufficient), implement:

• Daily food records to track actual intake 3
• Weekly weight checks to verify appropriate gain trajectory 3, 1
• Urine ketone testing if weight gain is inadequate or if there's concern about under-eating 3, 1

The presence of ketones indicates insufficient energy intake and requires immediate dietary adjustment 3, 1.

Quality Over Quantity: Nutrient-Dense Food Choices

The additional 300 kcal/day should come from nutrient-dense sources, not empty calories:

• Emphasize whole foods: fruits, vegetables, legumes, whole grains, nuts, seeds, fish, lean protein 1, 2, 5
• Avoid highly processed foods that provide calories without essential nutrients 5
• Include adequate protein: 0.75 g/kg/day plus an additional 10 g/day minimum 3, 4
• Distribute intake: 3 small-to-moderate meals plus 2-4 snacks to maintain stable blood glucose and prevent ketosis 3

Common Pitfall: Intentional Restriction to Avoid Weight Gain

Some women eat at maintenance (or restrict further) to avoid gaining weight or needing medical interventions. This is dangerous and should be actively discouraged 3. The evidence shows:

• Restricting to maintenance calories compromises fetal brain development through ketosis 3, 1
• Insufficient weight gain predicts worse perinatal outcomes than excessive gain in many cases 5
• First-trimester and early second-trimester gain are the strongest predictors of healthy outcomes 5

The message should be "eat better, not more" only applies to women already eating above their needs—not to those at maintenance 5.

Special Consideration: Metabolic Adaptations Are Insufficient at Maintenance

During pregnancy, the body undergoes remarkable metabolic adaptations including decreased amino acid catabolism, reduced urea synthesis, and increased protein synthesis 3. However, these conservation mechanisms only function optimally when dietary substrate (calories and protein) is adequate 3.

At maintenance-level intake, these adaptations cannot fully compensate, particularly in:

• Adolescent pregnancy 3
• Women with low pre-pregnancy BMI 3
• Women with inadequate protein intake 3

This results in compromised maternal-fetal protein accretion and poor outcomes 3.