Is fasting safe during pregnancy?

Fasting During Pregnancy: Safety and Recommendations

Fasting during pregnancy is generally not recommended, particularly for women with diabetes, as it carries potential risks to both maternal and fetal health, though evidence for healthy pregnant women without diabetes shows minimal adverse effects on most birth outcomes.

Key Considerations by Clinical Context

For Pregnant Women with Diabetes

Women with pre-existing diabetes (type 1, type 2) or gestational diabetes who insist on fasting constitute a high-risk group requiring intensive care. 1

• Fasting during pregnancy would be expected to carry a high risk of morbidity and mortality to both fetus and mother in diabetic women 1
• Elevated blood glucose and A1C levels in pregnancy are associated with increased risk for major congenital malformations 1
• Pregnant Muslim women are religiously exempt from fasting during Ramadan, yet some with known diabetes still insist on fasting 1

Critical metabolic concerns:

• Pregnancy is a state of increased insulin resistance with lower fasting glucose but substantially higher postprandial glucose and insulin levels 1
• Women with gestational diabetes may be at higher risk for ketosis even with moderately elevated blood glucose levels 2
• Hypocaloric diets (<1,200 calories per day) in obese women with gestational diabetes result in ketonemia and ketonuria 1

For Healthy Pregnant Women Without Diabetes

Current evidence suggests minimal clinically significant effects on most pregnancy outcomes, though data quality is limited.

Birth weight and gestational age:

• Little to no clinically significant effect on neonatal birthweight or preterm delivery has been found 3
• Systematic reviews show pooled odds ratios of 0.93-0.99 (95% CI 0.60-1.44 to 0.72-1.37) for preterm birth 4
• Pooled odds ratios of 1.05-1.37 (95% CI 0.87-1.26 to 0.74-2.53) for low birth weight 4
• One study found relative risk of low birth weight was 1.5 times higher in mothers fasting during first trimester compared to non-fasting mothers 5

Maternal effects:

• Fasting is mainly associated with signs and symptoms of maternal fatigue and dehydration, with minimal decrease in weight gain 3
• Weight gain during pregnancy in fasting women was approximately 0.4 kg less than non-fasting women 6
• Insufficient evidence exists regarding effects on maternal hypertension 3

Gestational diabetes:

• Conflicting data exist, with one study showing fasting during second trimester decreased risk of gestational diabetes (2.6% vs 8.3%, OR 1.51,95% CI 0.06-0.74) 6
• However, insufficient data overall on this association 3

Nutritional Requirements During Pregnancy

Adequate nutrition is essential to prevent ketosis and support fetal development.

• An evening snack is usually necessary to decrease potential for overnight hypoglycemia and fasting ketosis 1
• To prevent ketosis, adequate energy intake and appropriate distribution of meals and snacks is important 1
• An additional 300 kcal/day are suggested during second and third trimester 1
• Adequate protein intake (0.75 g/kg plus additional 10 g/day) is needed 1
• 400 µg/day of folic acid from fortified foods and/or supplements is recommended for prevention of neural tube defects 1

Diets that severely restrict macronutrients should be avoided:

• The ketogenic diet that lacks carbohydrates should be avoided 1
• Nutrient-dense whole foods including fruits, vegetables, legumes, whole grains, and healthy fats are recommended 1

Clinical Recommendations for Counseling

Obstetricians should engage patients in shared decision-making while demonstrating cultural and religious awareness. 3

For women with diabetes:

• Strongly advise against fasting due to high risk of maternal and fetal complications 1
• If patients insist on fasting, provide intensive monitoring and management 1

For healthy women without diabetes:

• Discuss the nuances in existing data, acknowledging that evidence shows minimal effects on most birth outcomes but with significant study limitations 3, 4
• Note that most studies suffer from methodologic limitations and significant heterogeneity 4
• Explain that earlier gestational age during Ramadan and husband's opinion influence adherence to fasting 7

If patients choose to fast:

• Offer medical recommendations, closer observation, and support to reduce harm and hardship 3
• Monitor for signs of dehydration and maternal fatigue 3
• Ensure adequate fluid intake when not fasting 1
• Consider more frequent antenatal testing, as fasting may affect nonstress tests, amniotic fluid levels, and biophysical profile scores 3

Important Caveats

• Current literature on long-term effects of fasting on offspring suggests possible adverse effects, but more data are required 3
• Quality of evidence is negatively impacted by variation in defining "fasting during Ramadan" in pregnancy, study size and design, and potential confounders 3, 4
• No evidence-based guideline currently exists for Muslim women regarding Ramadan fasting during pregnancy 4
• High-quality primary research studies collecting data on multiple confounders are needed 4