Table 3. Saturation or threshold effect analysis of waist circumference on female infertility stratified by moderate recreational activities using a two-piecewise linear regression model.
| Outcome: | Recreational activities (OR (95%CI) P value) | ||
|---|---|---|---|
| Deficient | Moderate | Vigorous | |
| Fitting by standard linear model | 1.01 (0.99, 1.04) 0.3309 | 1.02 (0.98, 1.06) 0.3490 | 1.06 (1.01, 1.10) 0.0081 |
| Fitting by two-piecewise linear model | |||
| Inflection point (K, cm) | 103 | 113.5 | 101.7 |
| waist circumference < K | 0.99 (0.96, 1.02) 0.6420 | 1.04 (0.99, 1.08) 0.1014 | 1.08 (1.03, 1.13) 0.0016 |
| waist circumference > K | 1.03 (1.00, 1.06) 0.0458 | 0.97 (0.91, 1.03) 0.2574 | 1.03 (0.98, 1.08) 0.2686 |
| Log-likelihood ratio | 0.013 | 0.008 | 0.075 |
Note: Covariates listed in Table 1 were adjusted except for recreational activities.