Risk factors for preeclampsia in multiparous women: Primipaternity versus the birth interval hypothesis

Introduction. To determine whether the risk of preeclampsia in multiparous women with a previous normal pregnancy is related to changing paternity or to prolonged birth interval, a retrospective study was conducted at the Lyell McEwin Health Service ( University of Adelaide). Methods. The study included all multiparous women known to the hospital because of their preceding 1st delivery in the same hospital followed by their 2nd and/ or 3rd ongoing pregnancy resulting in a delivery in the period 2001 - 2003. Case records were analyzed for birth interval, pregnancy interval, paternity and recognized risk factors such as booking weight and smoking. For the analysis both the International Society for the Study of Hypertension in Pregnancy (ISSHP) definition and the more recently introduced classification by the Australian Society for the Study of Hypertension in Pregnancy (ASSHP) were used. Results. In the 656 women in this study cohort, 148 ( 26.2%) women had a different partner in their 2nd and/ or 3rd ongoing pregnancy. Using the ISSHP definition for preeclampsia, changing partners had an odds ratio (OR) of 1.304 (95% CI 0.43 - 3.99); using ASSHP criteria an OR of 1.556 (95% CI 0.6506 - 3721); and looking at the combined group of pregnancy-induced hypertensive disorders an OR of 1.99 (95% CI 1.01 - 3.89). A longer birth interval if anything was associated with a lower risk of preeclampsia (non-significant), whatever definition was used. Also the inter-pregnancy interval did not show a consistent relation with the risk for developing a hypertensive complication. Conclusions. The results of this study on risk factors for preeclampsia in multiparous women appear to be in line with the primipaternity hypothesis, but are in direct contrast with the so-called birth interval hypothesis.