Why is light-headedness and occasional dizziness a common symptom for women in their second trimester of pregnancy?
1) Maternal myoglobin production has increased and stores more oxygen in the mother's muscles to prepare for labor.
2) Pressure from the expanding uterus makes breathing difficult, thus limiting the amount of oxygen exchange with the blood supply.
3) The increased affinity for oxygen demonstrated by fetal hemoglobin removes too much oxygen from the maternal blood supply.
4) While the maternal circulatory system has expanded to accommodate the needs of the growing fetus, the production of blood itself needs to fill in the new capacity.
