Relationship between placentation and maternal serum alpha-fetoprotein in twin pregnancies

Maternal serum alpha-fetoprotein (MSAFP) concentration is raised in twin pregnancies during the second trimester. The approximate doubling of seAFP level in uncomplicated twin pregnancies seems logical, considering the doubled fetal source of AFP, even though the seAFP level is not always increased in twin pregnancies. What factors can influence this phenomenon? With this in mind, we have examined the seAFP concentration in 90 successive twin pregnancies with known outcome. The relationship between seAFP level and the type of placentation is demonstrated.