Weight adjustment of serum markers in early first-trimester prenatal screening for Down syndrome

Objective To assess whether existing weight correction formulas for PAPP‐A and free‐beta‐hCG developed for weeks 11 to 14 can be applied to pregnancies in weeks 8 to 10. Methods Development of formulas based on limited data sets of 8‐ to 10‐week pregnancies and comparison with existing formulas. Calculation of median MoMs adjusted with different formulas for weight correction. Results Weight correction formulas for the gestational age of 11 to 14 weeks were not appropriate in the 8‐ to 10‐week gestational age interval for PAPP‐A, whereas existing weight correction formulas could be applied to free‐beta‐hCG, independent of gestational age interval. Conclusion If PAPP‐A is used in different gestational age intervals, weight corrections should be developed for the interval. Copyright © 2005 John Wiley & Sons, Ltd.