Total alkaline phosphatase levels by gestational age in a large sample of pregnant women

Total alkaline phosphatase (tALP) levels rise physiologically in maternal serum during pregnancy, and excessively so in certain conditions. However, current reference values are dated, nonlinear, and based on small samples. Factors related to variation in tALP remain unexplained. Thus, our goals in this study were to establish a physiological development curve for tALP within low-risk pregnancies and to evaluate the factors influencing tALP values.This was a single-center, retrospective, observational study. All patients who delivered a live singleton infant at our center from January 1, 2011 to May 31, 2019, and had a tALP assay during pregnancy, were included regardless of the gestational age at which the assay was conducted.A total of 2415 pregnancies were included. Median tALP decreased during the first trimester, it increased slightly during the second trimester, and then increased sharply during the third trimester. Factors associated with a significant increase in tALP were chronic histiocytic intervillositis, cholestasis, multiple pregnancies, liver disease, preeclampsia, smoking, and low weight for gestational age. Conversely, gestational diabetes was associated with a discrete decrease in tALP.Our large sample allowed establishment of tALP reference curves based on gestational age. To interpret these results more thoroughly, factors that influence tALP rates should be further scrutinized.