Table 4.
Threshold effect analysis of WWI, BMI, WC and ABSI on infertility using a two-piecewise linear regression model.
| WWI | BMI | WC | ABSI | |
|---|---|---|---|---|
| Fitting by standard linear model | ||||
| OR1 (95%CI2) P-value |
1.42 (1.22, 1.65) <0.001 | 1.03 (1.02, 1.05) <0.001 |
1.02 (1.01, 1.02) <0.001 | 1. 04 (1.02, 1.07) 0.002 |
| Fitting by two-piecewise linear model | ||||
| Breakpoint (K) | 12.34 | 19.40 | 71.60 | 79.58 |
| OR1 (<K) | 1.53 (1.29, 1.82) <0.001 | 0.66 (0.46, 0.96) 0.03 |
0.93 (0.78, 1.10) 0.37 | 1.02 (0.96, 1.08) 0.5417 |
| OR2 (>K) | 0.56 (0.19, 1.67) 0.2962 | 1.04 (1.02, 1.05) <0.001 |
1.02 (1.01, 1.02) <0. 001 | 1.06 (1.02, 1.11) 0.0089 |
| OR2/OR1 | 0.37 (0.11, 1.16) 0.088 | 1.56 (1.07, 2.27) 0.019 |
1.10 (0.93, 1.31) 0.288 | 1.04 (0.96, 1.14) 0.3204 |
| Logarithmic likelihood ratio test P-value | 0.073 | 0.034 | 0.313 | 0.324 |
Adjusted for age, ratio of family income to poverty, race, education level, marital status, smoked at least 100 cigarettes, had at least 12 alcohol drinks/1 year, age when first menstrual period occurred, ever treated for a pelvic infection/PID, ever taken birth control pills, had regular periods in past 12 months.