Abstract： Objective:Chemiluminescence immunoassay was used to detect the levels of anticardiolipin antibody (aCL) -IgA/IgG/IgM and anti-β2-glycoprotein Ⅰ antibody (aβ2GPⅠ) -IgA/IgG/IgM in healthy non-pregnant and pregnant women to explore the changes of antiphospholipid antibody in different pregnancy periods.Methods:This prospective study was conducted in Shandong Provincial Maternal and Child Health Care Hospital Affiliated to Qingdao University, involving normal pregnant women who underwent prenatal examination and healthy non-pregnant women with no history of adverse pregnancy who underwent progestational eugenic health examination from April 2020 to August 2021. The levels of aCL-IgA/IgG/IgM and aβ2GPⅠ-IgA/IgG/IgM were detected using BIO-FLASH chemiluminescence immunoassay analyzer and P95 as well as P99 were calculated, respectively. The difference in the six data between non-pregnant and pregnant women was compared using Mann-Whitney U test. Kruskal-Wallis H test was used to compare the change of each antibody in different pregnancy periods and Spearman correlation was used to analyze the correlation between different trimester and the levels of aCL-IgA/IgG/IgM and aβ2GPⅠ-IgA/IgG/IgM. Results:A total of 454 cases met the inclusion criteria, and 435 cases were included in the analysis after excluding 19 cases, among them 110 were non-pregnant women and 325 were pregnant women, including 110 cases in the first trimester (≤13 +6 weeks), 110 cases in the second trimester(14 +0-27 +6 weeks), and 105 cases in the third trimester (≥28 weeks). P99 value of aCL-IgA/IgG/IgM and aβ2GPⅠ-IgA/IgG/IgM in the non-pregnant women were 7.31, 14.70, 7.92, 3.58, 13.60, and 4.95 CU, which in the pregnant women were 5.90, 12.78, 5.70, 1.60, 10.65, and 3.90 CU, and were all lower than the cut-off value of 20 CU that given by the analyzer manufacturer. The levels of aCL-IgA/IgG/IgM, and aβ2GPⅠ-IgG/IgM in the pregnant women were significantly decreased comparing with the non-pregnant women [aCL-IgA: 1.90 CU (1.40-2.70 CU) vs 2.90 CU (2.20-3.83 CU), Z=－7.14; aCL-IgG: 3.00 CU (2.20-4.50 CU) vs 6.10 CU (4.20-7.83 CU), Z=－10.26; aCL-IgM: 1.40 CU (1.10-2.30 CU) vs 2.65 CU (2.08-3.73 CU), Z=－8.87; aβ2GPⅠ-IgG: 3.50 CU (2.60-4.90 CU) vs 4.75 CU (3.60-5.93 CU), Z=－5.45; aβ2GPⅠ-IgM: 0.70 CU (0.50-1.20 CU) vs 1.00 CU (0.60-1.53 CU) , Z=－3.73; all P<0.001]. The aCL-IgA level in the third trimester was higher than those in the first and second trimester (both P<0.05). The levels of aCL-IgG/IgM in the second trimester and aβ2GPⅠ- IgG in the second and third trimesters were significantly decreased than those in the first trimester (all P<0.05). Spearman analysis showed that aCL-IgG/IgM, aβ2GPⅠ-IgA/IgM had no significant correlation with the pregnancy period (the first, second and the third trimester) (all P>0.05). However, a weak correlation between the aCL-IgA, aβ2GPⅠ- IgG and the pregnancy period was observed ( r=0.28 and－0.49, both P<0.001) Conclusions:P99 value of aCL-IgA/IgG/IgM and aβ2GPⅠ-IgA/IgG/IgM levels in normal pregnant women and non-pregnant women are lower than the cut-off value of 20 CU given by the analyzer manufacturer. The levels of aCL-IgA/IgG/IgM and aβ2GPⅠ-IgG/IgM during pregnancy are lower than those before pregnancy and fluctuate with the pregnancy period, but have no significant correlation with the pregnancy period. The clinical diagnosis of antiphospholipid syndrome should be made according to the cut-off values of aCL-IgA/IgG/IgM and aβ2GPⅠ-IgA/IgG/IgM determined by each laboratory.