Placental transfer

The placenta selectively excludes various substances from crossing from the maternal to the fetal circulation. There is also selective transfer of material from fetus to mother. Examples are outlined below:

• immunoglobulins - IgA and IgM are excluded from crossing the placenta. Thus IgM antibodies in the newborn indicate a response to intrauterine infection. IgG is selectively transferred across the placenta.
• conjugated bilirubin only crosses the placenta slowly from fetus to mother. This is in contrast to transfer of unconjugated bilirubin which is rapidly transferred from fetus to mother via active transport.
• warfarin will pass from the maternal to the fetal circulation. This is in contrast to heparin, that will not cross the placenta.
• maternal Grave's disease can cause transient neonatal thyrotoxicosis because thyroid stimulating immunoglobulin is of IgG class.