Mixed

Prenatal exposure to severe famine during the third trimester of gestation causes a significant reduction in birth weight, whereas exposure during the first trimester is associated with an increase in birth weight.

This historical natural experiment demonstrates that the timing of nutritional deprivation during pregnancy has distinct, opposing effects on fetal growth. Third-trimester starvation reduces birth weight, while first-trimester starvation is associated with increased birth weight, likely due to adaptive placental mechanisms. This highlights that 'malnutrition' is not a monolithic concept; its impact depends entirely on the developmental stage of the fetus.