Thank you for your question. To clarify-the unbound fraction of the drug is the pharmacologically active portion. Since the maternal plasma albumin decreases during pregnancy, this allows more unbound drug circulating (for drugs that are protein bound, such as digoxin). The fetal albumin progressively increases over gestation, so more of the drug (since more is unbound and thus available to cross the placenta) can get to the fetus, where the higher albumin allows it to reach higher concentrations in the fetus. Hope that helps. Thanks for reading the article so carefully!!

Deb McCarter-Spaulding, RN