Fig. 2

The comparison of Serum CRP, C3, C4 and ferritin among three different trimesters. Distribution of inflammatory factors including C-reactive protein (CRP), C3, C4 and ferritin across different trimesters (p < 0.01 for CRP, C3 and ferritin in term birth group at three different trimesters). The first trimester defined as gestational age less than 14 weeks, of which PTB group (n = 68), TB group (n = 136). In the first trimester, serum concentrations of CRP and C3 in PTB group were significantly higher than the TB group (group effect, p < 0.05). For C4 and ferritin, there was no significant difference between preterm and term group (group effect, p > 0.05). The second trimester gestational age ranged from 14 to 27 weeks, with the PTB group (n = 116) and the TB group (n = 232). The third trimester defined as the gestational age of 28 weeks or more, the PTB group (n = 22), the TB group (n = 44). In any stage of the second and third trimester, the inflammation indicators (i.e. ferritin, CRP, C3 and C4) were not significantly difference with PTB