RESULTS
The total number of fetal records from 2011 to 2014 in the JECS was 104,102. Of these, 1,994 and 3,278 records were excluded for multiple gestations and insufficient DII data, respectively. Then, 10,432 participants were excluded for having insufficient data. After applying our inclusion criteria, 88,398 participants were eligible for the present study and were then categorised into two groups based on the presence or absence of endometriosis (self-reported) (n=3,249, endometriosis group; n=85,149 without endometriosis group). Finally, both groups were divided into five categories according to quintiles of their DII score (Figure 1).
Table 1 summarises the basic characteristics of the participants according to the presence of endometriosis. The mean maternal age and maternal age categories were significantly different between the two groups (p<.001 and p<0.001, respectively). The mean DII was significantly higher in the non-endometriosis group (p<0.001). In the endometriosis group, the rate of uterine myoma, adenomyosis, and ART pregnancy were significantly higher than those in the non-endometriosis group. The categories of maternal education, household income, and BMI were significantly different between the two groups (p<0.001, p<0.001, and p=0.031, respectively).
Table 2 summarises the trend of obstetric outcomes for both groups according to the DII category. The prevalence of PTB <37 and <34 weeks, LBW <2500 g, and HDP were 4.5%, 0.9%, 7.9%, 0.5%, and 2.8%, respectively, for the non-endometriosis group, and 6.2%, 1.2%, 10.0%, 0.7%, and 3.2%, respectively, for the endometriosis group. Among women with endometriosis, the incidence of LBW <2500 g decreased in the DII group (p=0.008). Among women with endometriosis, the incidence of PTB <34 weeks and LBW <1500 g significantly decreased in the DII group (p=0.040 and p=0.003).
Table 3 summarises the aORs of obstetric complication according to DII category for both the endometriosis and non-endometriosis group, with Q1 (most pro-inflammatory category) as the reference. The multiple regression analysis shows decreased risk for PTB <34 weeks in Q3 (aOR 0.77, 95% CI 0.62–0.97), Q4 (aOR 0.77, 95% CI 0.61–0.96), and Q5 (aOR 0.80, 95% CI 0.64–0.998) for the endometriosis group. For the endometriosis group, Q5 groups had significantly decreased risk of PTB <34 weeks (aOR 0.35, 95% CI 0.12–0.99) and LBW <1500 g (aOR 0.13, 95% CI 0.03–0.61). For women with endometriosis without ART, Q5 still significantly decreased the risk of PTB <34 weeks (aOR 0.25, 95% CI 0.07–0.83) and LBW <1500 g (aOR 0.07, 95% CI 0.01–0.60).