In addition, similar studies have reported a significant association of elevated C3a and C5a levels and decreased CD59 levels with various pregnancy complications, including gestational hypertension, preterm delivery, and intrauterine growth restrictions.[39,40] Our research adds important evidence that excessive complement activation in complicated pregnancies may be associated with many pre-existing conditions, which are triggered by IVF-ET treatment. This evidence concerns the gene C5 and preeclampsia.