2.5 Sample size calculation
To test the hypothesis that GCF-PLAP concentrations are significantly
higher during the first trimester in pregnancies that will subsequently
develop PE, the estimated sample size was calculated based on previously
published data41 and in our previous observations of
differences between GCF-PLAP concentrations in women with PE and
normotensive pregnant women (2044 ± 217 and 1880 ± 82 pg/ml; mean ±
standard deviation, respectively)99. To test the
hypothesis of mean differences in GCF-PLAP between patients affected by
PE and heathy controls, a minimum cohort size of 406 pregnant women was
calculated based on the following assumptions: a 6.4% prevalence of PE
in the entire cohort; a significance level of 5%; a power of 80%; a
two-sided test; and a loss-to-follow-up of 5%.