Circulating levels of pregnancy-specific beta1-glycoprotein and human placental lactogen in the third trimester of pregnancy: their relationship to parity, birth weight, and placental weight.

Circulating levels of pregnancy-specific beta1-glycoprotein (SP1) and human placental lactogen (HPL) were measured in 153 normal subjects during the third trimester of pregnancy. The levels of SP1 and HPL showed a skewed distribution and rose progressively to reach a plateau by the 36th week. The normal range was calculated by ranking the data and division into centiles as well as by logarithmic transformation of the values. A low but significant correlation was observed between SP1 and HPL levels, SP1 and birth weight. There was also a correlation between HPL levels and placental weight.