Because of accidental pregnancies, there are some treatments denied to all fertile women regardless of choice. Ussually they are those that cause horrible birth defects (limb reductions etc) or make pregnancy deadly to the mother. Given the links between oxygen and injuries like FAS, this hemoglobin treatment may be one of that group.
Example: Acutane was once used to treat acne in teenagers. Many/most doctors didnt give it to teenage girls regardless of whether they were sexually active or on the pill. Mistakes happen. That drug would do horrible things to a fetus.