He YD, Xu BN, Song D, et al. - Since a key role of the complement system in normal placentation is known, and successful pregnancy essentially requires delicate regulation of complement system activation, therefore, researchers defined the normal range of complement components in circulation during various stages of pregnancy in this prospective investigation. They used an immunoturbidimetric assay to measure plasma levels of complement factor B (CFB), C1q, complement factor H (CFH), C3, C3c, and C4. They used ELISA to ascertain levels of mannan-binding lectin (MBL), C3a, C5a, and soluble C5b-9 (sC5b-9) at different time points of pregnancy. They analyzed 733 and 65 plasma samples from 362 women with a normal pregnancy and from nonpregnant women, respectively. For CFB, CFH, MBL, C3c, C4, and C3a levels in the first trimester of pregnancy, the values were 414.5±85.9 mg/L, 381.0±89.0 mg/L, 4274.5±2752 ng/mL, 1346.9±419.8 mg/L, 357.4±101.8 mg/L, and 182.5±150.0 ng/ml, respectively. During pregnancy, a gradual rise in C3 and C4 levels was noted. Compared with non-pregnant women, the observed C1q, C5a and sC5b-9 levels in the first and second trimesters were almost the same. Based on the findings, experts concluded that plasma levels of complement system components may be affected by pregnancy itself.