In our study, from January 2013 to December 2017, 2300 couples in the cohort were selected from 34,034 visits to pre-pregnancy center based on a ratio of 15:1; However, 48 (2.09%) couples who were worried about disclosing their private information refused to participate in the investigation; 64 (2.78%) were lost to follow-up. Finally, 1839 couples with first child intention, 338 couples with second child intention included in this study (the recruitment flow chart is shown in Fig. 1).
Among all couples who plan to conceive (n=2177, the overall incidence of infertility was 16.95% (95% CI, 15.37%-18.53%; infertility=369, fertility=1803). The incidence of “infertility of first child intention” was 19.30% (95% CI, 17.50%-21.11%; infertility=355, fertility=1484). By contrast, the incidence of “infertility of second child intention” was 4.14% (95% CI, 2.01%-6.28%; infertility=14, fertility=324).
Table 1 shows the differences in the sociodemographic and socioeconomic characteristics of couples in this study. The mean (±standard deviation [SD]) age was 29.76 (±3.71) years for overall women and 31.36 (±4.39) years for overall men. Among couples with “first child intention”, the mean (±SD) age was 29.50 (±3.52) for women and 31.12 (±4.22) for men. Among couples with “second child intention”, the female and male mean (±SD) age was 31.11 (±4.36) and 32.53 (±4.97). Furthermore, the mean BMI (±SD) values for overall women and men were 21.08 (±2.69) kg/m2 and 23.67 (±2.82) kg/m2, respectively. Among couples with “first child intention”, the mean BMI (±SD) was 21.07 (±2.70) kg/m2 for women and 23.71 (±2.87) kg/m2 for men. Among couples with “second child intention”, the mean BMI (±SD) was 21.15 (±2.60) kg/m2 for women and 23.52 (±2.59) kg/m2 for men. Most women and men completed junior college or university or above. More than 90% of women were employed. And the largest percentage of households had annual incomes of more than 20,000 yuan.
In the “couples with first child intention” group, the proportions of both women and men with older age, higher BMI and lower incomes was significantly greater in the infertility group than in the fertility groups. Furthermore, women with low education were more likely to be infertility in this group. In the “couples with second child intention” group, the proportions of women with older age, low education and man with low education was significantly greater in the infertility group than in the fertility groups.
Figure 2 shows the crude unadjusted ORs and their 95% CIs for the association between infertility and female medical history in two groups. In the “couples with first child intention” group, compared with women who had normal menstruation, women with longer menstrual cycles, longer menstrual durations were more likely to be infertile. Regarding the medical history, the occurrence of infertility was associated with factors such as leiomyoma, ovarian cysts, endometrial polyps, endometriosis, polycystic ovarian syndrome (PCOS), history of lower genital tract infection (mycoplasma, chlamydia and condyloma acuminate). Moreover, among infertile couples, a high proportion of women had a history of surgery such as uterine myomectomy, salpingostomy, transcervical polyp resection, and hysteroscopic adhesiolysis, which were associated with a significantly higher risk of infertility. In terms of “couples with second child intention” group, the crude OR of infertility among women with later menarche and history of leiomyoma was significantly lower than that of women who did not.
Regarding the male history of disease (Table 2), prostatitis, lower genital tract infection (mycoplasma and chlamydia) were factors that could lead to infertility in the “first child intention” group. However, no significant differences were found in male history in “second child intention” group between infertility and fertility.
Multivariate Analysis Of Risk Factors For Infertility
Table 3 presents the results of the multivariate analysis of the risk of infertility. For couples intending to have first child, high BMI (≥24 kg/m2) and older age (>35 years) for women and low BMI (<18.5 kg/m2) for men were found to be risk factors for infertility. As for female menstrual history, the results indicated that women with longer menstrual durations (OR, 4.47; 95% CI, 2.25-8.88) were at a greater risk for infertility. Moreover, women with a history of endometrial polyps (OR, 2.52; 95% CI, 1.28-4.97), or PCOS (OR, 6.72; 95% CI, 1.79-7.39), or endometriosis (OR, 2.52; 95% CI, 1.27-4.97), or mycoplasma infection in the lower genital tract (OR, 1.54; 95% CI, 1.09-2.40) were more likely to experience infertility than women who did not. Correspondingly, previous salpingostomy (OR, 3.44; 95% CI, 1.68-7.07) was also associated with a higher risk of infertility.
Turning now to “second-child intention” group, the ORs were not significant among women with age range from 35-39; however, the ORs become significant when female age over 40 (OR, 7.36, 95% CI: 1.01–53.84). Surprisingly, female history of leiomyoma (OR, 5.60; 95% CI, 1.06-29.76) was significant risk factors of infertility in “couples with second child intention” group, while this factor is not significantly different in “couples with first child intention” group (OR, 1.38; 95% CI, 0.92-2.07). Furthermore, women who had experienced infertility were more likely to have history of endometriosis (OR, 38.68; 95% CI, 1.16-1286.82).