C4A and preeclampsia: Nevertheless, despite inconsistencies in different circulating CS components, a systematic meta-analysis of selected 41 studies out of a total of 456 studies has retrieved results consistently reporting reduction of C4, C3, and factor H and increase of C4d, Bb, factor D, C3a, C5a, and MAC or C5b-9 in maternal circulation during preeclampsia than in women with normal pregnancies (395).