The mean ± standard deviation (SD) serum concentrations of PCBs in fathers and mothers were 0.38 ± 0.21 and 0.28 ± 0.16 ng g−1 wet weights, respectively (Table 2). The mean concentrations of PCBs stratified by a number of deliveries in mothers are shown in Table 2. PCB concentrations in the fathers were higher than in the mothers, and among the mothers, serum PCB concentrations were lower as the number of deliveries was greater. PCB levels in this study are comparable or slightly lower than the serum levels of previous cohort studies in Japan, USA, and European countries (Table 3) (Govarts et al. 2012; Inoue et al. 2006; Patterson et al. 2009). Based on the stepwise forward selection results, consumption of fish and eggs was selected along with age and number of delivery for the model of mothers by WAIC (Tables 4 and 6). In mothers, age [β = 0.26, 95% CI (0.23, 0.29)] and fish [β = 0.055, 95% CI (0.029, 0.082)] and egg consumptions [β = 0.025, 95% CI (−0.00027, 0.052)] were positively and a number of deliveries [β = −0.18, 95% CI (−0.21, −0.16)] was negatively associated with PCB concentrations in mothers (Table 6). However, in our analysis, only age [β = 0.25, 95% CI (0.19, 0.32)] was selected for the fathers’ model (Tables 5 and 6).Table 2PCB concentrations (ng/g wet wt.) in serum from fathers and mothersMeanStandard deviationMin25%50%75%MaxFather (n = 219)0.380.210.050.230.320.491.2Mother (n = 1477)0.280.160.050.180.250.351.3Delivery status of mothersA number of deliveries: 0 (n = 550)0.320.170.050.210.280.391.3A number of deliveries: 1 (n = 644)0.260.140.050.170.240.331.3A number of deliveries: 2 (n = 234)0.230.140.050.140.210.290.79A number of deliveries: 3 (n = 37)0.220.150.050.120.190.250.71A number of deliveries: 4 (n = 10)0.150.0820.050.0680.160.220.26A number of deliveries: 5 (n = 2)<0.1 Table 3Comparison of serum concentrations of PCBs (pg g−1 wet wt.) in participants analyzed in this study with previous dataAgeMeanStandard deviationMin25%50%75%MaxReferencesFather (n = 219)32.9 ± 6.00.380.210.050.230.320.491.2This studyMother (n = 1477)31.0 ± 5.00.280.160.050.180.250.351.3This studyJapanese mother (n = 89)*20–29 years (50.6%)30–39 years (44.9%)40–49 years (5.5%)0.360.0620.210.300.451.3Inoue et al. 2006 Mothers from 12 European birth cohorts (n = 7762: CB153)>20% of mothers were <25 years of age at delivery and in two populations >20% were >35 years of age0.180.160.14Govarts et al. 2012 National Health and Nutrition Examination Survey (2003–2004): USA12–19 years (31.2%)20–39 years (24.5%)40–59 years (20.3%)+60 years (24.0%)Male (n = 928)0.835**0.8141.62Patterson et al. 2009 Female (n = 938)0.805**0.8241.65Patterson et al. 2009 *Adjusted by reported average serum lipid level (7.9 g/L) (Longnecker et al. 2003)**Geometric mean Table 4Selection of prediction model based on mothers’ dataset by WAICWAICPCB ~ age−1843.5PCB ~ age + a number of deliveries−2012.9PCB ~ age + a number of deliveries + BMI−2011.4PCB ~ age + a number of deliveries + cereals−2012.2PCB ~ age + a number of deliveries + potatoes and starches−2011.5PCB ~ age + a number of deliveries + vegetables−2013.3PCB ~ age + a number of deliveries + fruits−2011.4PCB ~ age + a number of deliveries + fish and shellfish−2028.5PCB ~ age + a number of deliveries + meats−2011.3PCB ~ age + a number of deliveries + eggs−2014.2PCB ~ age + a number of deliveries + milk−2011.6PCB ~ age + a number of deliveries + fats and oils−2011.5PCB ~ age + a number of deliveries + fish and shellfish + BMI−2027.5PCB ~ age + a number of deliveries + fish and shellfish + cereals−2027.0PCB ~ age + a number of deliveries + fish and shellfish + potatoes and starches−2027.8PCB ~ age + a number of deliveries + fish and shellfish + vegetables−2027.9PCB ~ age + a number of deliveries + fish and shellfish + fruits−2027.0PCB ~ age + a number of deliveries + fish and shellfish + meats−2026.4 PCB ~ age + a number of deliveries + fish and shellfish + eggs −2030.2 PCB ~ age + a number of deliveries + fish and shellfish + milk−2028.3PCB ~ age + a number of deliveries + fish and shellfish + fats and oils−2026.7PCB ~ age + a number of deliveries + fish and shellfish + eggs + BMI−2029.2PCB ~ age + a number of deliveries + fish and shellfish + eggs + cereals−2028.4PCB ~ age + a number of deliveries + fish and shellfish + eggs + potatoes and starches−2029.7PCB ~ age + a number of deliveries + fish and shellfish + eggs + vegetables−2029.4PCB ~ age + a number of deliveries + fish and shellfish + eggs + fruits−2029.1PCB ~ age + a number of deliveries + fish and shellfish + eggs + meats−2028.3PCB ~ age + a number of deliveries + fish and shellfish + eggs + milk−2030.0PCB ~ age + a number of deliveries + fish and shellfish + eggs + fats and oils−2028.4*Italicized model was selected with the smallest WAIC Table 5Selection of prediction model based on fathers’ dataset by WAICWAIC PCB ~ age −172.8 PCB ~ age + BMI−172.4PCB ~ age + cereals−171.0PCB ~ age + potatoes and starches−172.5PCB ~ age + vegetables−169.9PCB ~ age + fruits−171.9PCB ~ age + fish and shellfish−172.0PCB ~ age + meats−170.9PCB ~ age + eggs−171.4PCB ~ age + milks−171.7PCB ~ age + fats and oils−170.7PCB ~ age + potatoes and starches + BMI−172.2PCB ~ age + potatoes and starches + cereals−171.2PCB ~ age + potatoes and starches + vegetables−170.0PCB ~ age + potatoes and starches + fruits−171.0PCB ~ age + potatoes and starches + meats−171.1PCB ~ age + potatoes and starches + fish and shellfish−171.0PCB ~ age + potatoes and starches + eggs−171.3PCB ~ age + potatoes and starches + milk−171.4PCB ~ age + potatoes and starches + fats and oils−171.2*Italicized model was selected with the smallest WAIC Table 6Empirical mean (mean), standard deviation of the mean (SD), and quantiles for each variable in selected prediction model for mothers and fathersMothersFathersCoefficientStandard deviation95% lower95% upperCoefficientStandard deviation95% lower95% upperIntercept−1.320.013−1.34−1.29−1.00.032−1.1−0.93Age0.260.0140.230.290.250.0330.190.32A number of deliveries−0.180.013−0.21−0.16NAFish and shellfish0.0550.0130.0290.082OmittedEggs0.0250.013−0.000270.052Omitted“Omitted” indicates factors eliminated by stepwise procedures NA not analyzed