OC26.06: First trimester maternal serum level of pregnancy associated plasma protein A is an independent factor of fetal maxillary bone length

Abstract

To derive a normogram of fetal maxillary bone length for a Chinese population and to study whether first trimester maternal serum levels of pregnancy associated plasma protein A (PAPP-A) is an independent factor of fetal maxillary bone length. This was a prospective study of 607 Chinese women with a singleton pregnancy who attended our first trimester screening for Down syndrome programme. The subjects had the fetal crown-rump length (CRL), nuchal translucency, maxillary bone length, maternal serum PAPP-A and free beta-hCG (fβ-hCG) levels measured. A normogram of maxillary bone length was derived using normal pregnancies without date problem. The correlations between maxillary length, CRL, PAPP-A and fβ-hCG levels were studied, after correction for gestational dependency using z-score transformation for the ultrasound markers (z-MAX and z-CRL), and logarithmic transformation of multiple of medians (MoM) for the biochemical markers. Positive correlations were further analysed with multiple regression. The mean gestational age at screening was 124 weeks (SD: 4 days). Curve estimation analysis showed that a linear relationship fit best between maxillary bone length and CRL (r = 0.826; p < 0.001), and between maxillary length and gestational age (r = 0.754; SD = 0.71; p < 0.001). There were significant positive correlations between z-MAX and z-CRL (r = 0.627; p = < 0.001), z-MAX and log10PAPP-Amom (r = 0.239; p = < 0.001). Multiple regression analysis showed that both z-CRL (p = < 0.001) and log10PAPP-A < STARTSUBmom (p = 0.048) were independent factors for z-MAX. Both CRL and maternal levels of PAPP-A are independent factors for the fetal maxillary length measured during the first trimester. The positive correlation between PAPP-A levels and fetal maxillary length is consistent with the known biological function of PAPP-A on bone growth. This association must be adjusted for when both PAPP-A and maxillary length are combined for screening of Down syndrome.