Pregnancy requires a steady supply of nutrients to support the mother’s metabolism and the developing fetus. When a pregnant person goes without food for a full 24-hour period—whether due to severe appetite loss, illness like hyperemesis gravidarum, or intentional fasting—the body is forced to rapidly adapt. This acute lack of caloric intake triggers responses that shift the body’s energy sourcing. These shifts can have immediate effects on the mother and potential consequences for the baby.
Immediate Maternal Physiological Changes
A complete absence of food for a full day causes the pregnant body to quickly deplete its primary energy source, which is circulating glucose. Pregnancy is already characterized by a state of accelerated starvation, meaning the body switches to alternative fuel sources faster than in a non-pregnant state. This rapid depletion can lead to maternal hypoglycemia, or low blood sugar, which manifests with symptoms like dizziness, shaking, sweating, and difficulty thinking clearly.
Once glucose stores are exhausted, the body initiates lipolysis, the breakdown of stored fat, to generate energy. This process produces molecules called ketones, resulting in a metabolic state known as ketosis.
Ketosis signals that the mother’s body is struggling to meet its energy demands. If the lack of food is due to severe vomiting, the inability to keep fluids down can lead to significant fluid and electrolyte imbalances. Dehydration can further intensify the physical symptoms, making the pregnant person feel extremely tired and weak.
Risks to Fetal Growth and Development
While the placenta acts as a protective barrier, the fetus depends on the mother’s nutritional state, and a 24-hour fast can alter the intrauterine environment. The fetus is generally protected from acute maternal hypoglycemia, but the shift to maternal ketosis introduces a new factor. Ketones, produced by the mother’s fat breakdown, can cross the placenta.
The main concern with elevated maternal ketones is their impact on fetal neurodevelopment, especially if the exposure is chronic or severe. Studies suggest a link between high maternal ketone levels and lower cognitive scores in childhood, though results are mixed and often linked to underlying conditions. For an acute 24-hour period of fasting, the risk is lower than for chronic malnutrition, but it still represents a suboptimal environment for fetal growth.
In the later stages of pregnancy, prolonged nutritional gaps can be associated with restricted fetal growth or a reduction in amniotic fluid volume. A long maternal fast before delivery has been associated with an increased risk of neonatal hypoglycemia, where the newborn’s blood sugar drops dangerously low shortly after birth. The timing of the deprivation matters, as risks differ between the first, second, and third trimesters.
When to Seek Medical Attention
While an isolated missed meal may not require medical intervention, a full 24-hour period without caloric or fluid intake warrants professional advice. A pregnant person should immediately contact their obstetrician or midwife if they experience persistent vomiting that prevents keeping down even small sips of water for more than 12 hours. Severe dehydration is a serious risk during pregnancy.
Immediate medical attention is necessary if the pregnant person shows signs of severe low blood sugar, such as profound confusion, extreme dizziness, or fainting spells. These symptoms indicate that the body’s compensatory mechanisms are failing and could signal a medical emergency.
If a pre-existing condition like diabetes is present, high ketone levels can rapidly escalate to diabetic ketoacidosis. This is a life-threatening complication that requires immediate hospital treatment.
If appetite loss or an inability to eat persists beyond a single day, or if there is evidence of weight loss, nutritional counseling and medical support are necessary. Supportive measures may include IV fluids or anti-nausea medication to ensure the safety of both the mother and the baby.