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Second- and third-trimester serum levels of placental proteins in preeclampsia and small-for-gestational age pregnancies



Background:  Poor placentation may perpetuate preeclampsia, but the presence of a major placental pathology has been questioned in cases of preeclampsia where the newborn has an appropriate birthweight for gestational age. On the other hand, poor placentation is also observed in the absence of preeclampsia, in pregnancies with small-for-gestational-age (SGA) fetuses. In late gestation, maternal serum levels of placental protein hormones are changed in both preeclampsia and SGA, but no longitudinal preonset studies are available for pregnancy-associated plasma protein A (PAPP-A), pregnancy-specific β1-glycoprotein (SP1) or human placental lactogen (HPL).

Methods:  In a nested case-control study we compared maternal serum levels of PAPP-A, SP1, HPL and placenta growth factor (PLGF) at 17, 25 and 33 weeks in pregnancies developing preeclampsia without fetal growth restriction (n = 28), or characterized by a growth-retarded fetus (n = 25), with gestation-matched controls (n = 65). The proteins were quantified using microplate enzyme immunometric assays and the serum levels at 17, 25 and 33 weeks compared between the three groups by nonparametric statistical tests.

Results:  In pregnancies with subsequent preeclampsia PAPP-A, SP1, HPL and PLGF were reduced at 17 weeks of gestation whereas at 25 and 33 weeks only PLGF remained below the controls. In growth-restricted pregnancies PAPP-A, SP1 and HPL were reduced at 17 weeks, and only HPL continued to be strongly affected thereafter.

Conclusion:  The reduced serum levels of the placental proteins PAPP-A, SP1 and HPL in the early second trimester (17 weeks) in pregnancies with subsequent preeclampsia or with fetal growth restriction involve an underlying role for the placenta in either pathology independent from the other.