Table 2 details the mean hemoglobin level and cumulative incidence (risk) of AIP for each category of parity.
Parous women who had not breastfed had a higher risk than any category who did, and also within each category of parity.
We extracted study-specific estimates of RR (odds ratios, rate ratios, and risk ratios) and their 95% confidence intervals (CIs) for highest versus lowest category of parity, age at first birth, breastfeeding, and age at menarche.
The models for these analyses were stratified for categories of parity.
Over multiple categories of parity, the RRs either were unaffected or showed a slight increase in the risk of AIP over increasing parity units.
Over multiple categories of parity, taking < 10.5 g/dl as the cutoff value of the hemoglobin level produced a similar result pattern to that found with a cutoff value of 11.0 g/dl, although the RRs were higher.
In the present study, the results obtained with high cutoff values were shifted towards a null risk ratio because the misclassified outcome was non-differential over the categories of parity.
In the fully adjusted MLLR models that were restricted to incident cases, women with HP pregnancies had a higher risk of AIP compared to those who had had fewer pregnancies (Risk Ratio, RR = 2.92; 95% CI 2.02, 4.59); the AIP risk increased in a dose-response fashion over multiple categories of parity.
The differences in risk of ovarian cancer that we observed could be due to chance or due to differences in reproductive and hormonal factors beyond the simple categories of parity and oral contraceptive use for which we were able to adjust.
In multivariable models, controlling for age, race, marital status, income, education, height, alcohol use, clinic site, and smoking, we again observed no association with fasting glucose but a trend toward increased insulin and HOMA-IR with higher categories of parity (Ptrend = 0.01 for insulin and 0.02 for HOMA-IR).
The likely mechanism for such an effect is not clear, and the differences in the risk for ovarian cancer, which we observed, could be due to chance or due to differences in reproductive factors beyond the simple categories of parity and oral contraceptive use for which we were able to adjust.
