Objective:To investigate the expression of Apo A Ⅳ during early pregnancy in mice and the expression of Apo A Ⅳ in the different stages of pregnant women;to analyze the role of Apo A Ⅳ during the process of embryo implantation and decidualization.Methods:Totally 84 mice were randomly divided into 2 groups:normal mated males and females rats were assigned into pregnant group(n=42);female rats mating with male rats after ligation were assigned into pseudopregnant group(n=42). All animals were purchased from the experimental animal center of Chongqing Medical University. ELISA was used to detect the expressions of serum Apo A Ⅳ and high density lipoprotein(HDL)in the pregnant and pseudopregnant rats which were pregnancy in d1 to d7days. A total of70 pregnant women were examined for serum levels of Apo A Ⅳ and HDL. Fifteen women in the first trimester(12 weeks)

15 women in the first trimester(13 weeks)and 40 women in the second trimester(15 to 18 weeks

10 cases per week)were enrolled from the Obstetrics and Gynecology Laboratory of the First Affiliated Hospital of Chongqing Medical University. Immunohistochemistry was performed to detect the ex pression of Apo A Ⅳ in pregnant mice uterus of d1

d5

d6 and d7. Results:Apo A Ⅳ and HDL were gradually increased with the number of days during early pregnancy in mice. There was a significant difference of the levels of Apo AⅣ and HDL between d2 to d7and d1(P<0.01). However

there was no significant difference in levels of Apo A Ⅳ and HDL in pseudopregnant group(P>0.05). In human specimens

the levels of Apo A Ⅳ and HDL were increased with the increase of gestation weeks. The expression levels of Apo A Ⅳ and HDL in serum of 12-week gestation were significantly lower than those in the later gestation weeks(P=0.000). Based on the results of immunohistochemistry

Apo A Ⅳ was slightly expressed in the glandular epithelium on d1

d5 and d6

it had a wide range of expression. On d7

it was strongly expressed in secondary decidual zone(P<0.05). Conclusion:The expression level of Apo A Ⅳ may be related to embryo development and endometrial stromal cells decidualization during early pregnancy.