Objective To assess trends in levels of biochemical markers, uterine artery (UtA) pulsatility index (PI) and maternal blood pressure changes over time and study their relationships in uncomplicated first-trimester pregnancies. Methods The study population comprised 86 women with singleton pregnancies. In each woman, a blood sample was collected at 6-7, 8-9, 10-11 and 12-13 weeks' gestation. At the same visit blood pressure was measured and ultrasound examination was performed to measure the crown-rump length and Doppler flow velocity waveform patterns of both UtAs. Serum concentrations of pregnancy-associated plasma protein-A (PAPP-A), free β-human chorionic gonadotropin (β-hCG), A disintegrin and metalloprotease domain-containing protein-12 (ADAM-12), placental protein-13 (PP-13) and placental growth factor (PlGF) levels were measured in thawed specimens using an automated time-resolved fluorescence assay. Summary curves were created to describe normal ranges and trends over time. The data were analyzed with a linear mixed model with the log-transformed marker values as dependent variables. This allowed for flexible modeling of patterns over time. Results Sixty-eight pregnancies had an uneventful outcome, with the birth of an appropriate-for-gestational-age (AGA) infant. In these pregnancies serum PAPP-A, ADAM-12, PP-13 and PlGF levels increased with gestational age. The UtA-PI decreased and the mean arterial blood pressure remained constant. There were no significant correlations between maternal age, birth-weight percentile, gender and blood pressure and any of the biochemical markers. The serum markers were highly correlated with each other except for β-hCG. A negative correlation was found between most biomarkers and UtA-PI, especially from 10 weeks onwards. Serum concentrations of ADAM-12 and PP-13 were lower in a small-for-gestational-age (SGA) subgroup born at term (n = 6), the former statistically significantly (P = 0.031), the latter non-significantly (P = 0.054), whereas UtA-PI was significantly higher (P = 0.02). Biomarker concentrations in 12 women delivering a large-for-gestational age infant did not differ from those delivering AGA neonates. Conclusion There is a relationship between biochemical markers of early placentation and downstream resistance to flow in the UtAs in low-risk uncomplicated pregnancies, indicating differences in placentation. In a small series of SGA infants born at term we could demonstrate differences as compared to normal pregnancies, with potential value for screening. © 2011 ISUOG. Published by John Wiley & Sons, Ltd.