Copeptin is not a useful biomarker for small-for-gestational-age: a case control study

Objective. To investigate copeptin as a biomarker for small-for-gestational-age. Methods. We conducted a nested case-control study on maternal copeptin levels measured in gestational week 12 and 19 and risk of small-for-gestational age. Cases were defined as pregnant women who delivered a small-for-gestational-age infant. Small-for-gestational age was defined as a birth weight -22% or less than expected according to gestational age (n = 39). Controls were pregnant women who delivered a normal-weight infant (n = 119). The copeptin ultrasensitive Kryptor kit (BRAHMS) was used to determine copeptin in maternal serum. We established reference ranges for copeptin by 95% prediction intervals with 90% confidence intervals. Paired and unpaired t-tests were performed to test the null-hypothesis of no difference in copeptin levels within and between the groups. Results. The reference intervals for copeptin in normal pregnancies were 1.24-5.51 pmol/L (90% confidence intervals on upper and lower limit were 1.13-1.37 and 5.00-6.08 pmol/L) at gestational week 12, and 1.30-5.09 pmol/L (90% confidence intervals were 1.19-1.42 and 4.65-5.57 pmol/L) at gestational week 19. Copeptin levels decreased from week 12-19 in cases (p = 0.02), whereas no change was observed in controls (p = 0.61). We found no difference in copeptin levels in cases compared to controls in gestational week 12 (p = 0.10) and week 19 (p = 0.81). Conclusion. The present study could not demonstrate copeptin as a novel biomarker for small-for-gestational-age.