Human placental lactogen, estradiol-17beta, and progesterone levels in the third trimester and their respective values for detecting twin pregnancy.

Plasma levels of HPL, P, and E2 was serially measured between weeks 30 to 36 in simplex and duplex pregnancies. Levels of both HPL and P were significantly higher in duplex than in simplex pregnancies. However, this was not the case for E2. There was a significant correlation between HPL and P levels. It is indicated that measurement of plasma P levels, as those of HPL levels, but not E2 levels is of value for detecting twin pregnancy.