Pre-eclampsia rates in the United States, 1980-2010: age-period-cohort analysis

Abstract

Objective: To estimate the contributions of biological aging, historical trends, and birth cohort effects on trends in pre-eclampsia in the United States.

Design: Population based retrospective study.

Setting: National hospital discharge survey datasets, 1980-2010, United States.

Participants: 120 million women admitted to hospital for delivery.

Main outcome measures: Temporal changes in rates of mild and severe pre-eclampsia in relation to maternal age, year of delivery, and birth cohorts. Poisson regression as well as multilevel age-period-cohort models with adjustment for obesity and smoking were incorporated.

Results: The rate of pre-eclampsia was 3.4%. The age-period-cohort analysis showed a strong age effect, with women at the extremes of maternal age having the greatest risk of pre-eclampsia. In comparison with women delivering in 1980, those delivering in 2003 were at 6.7-fold (95% confidence interval 5.6-fold to 8.0-fold) increased risk of severe pre-eclampsia. Period effects declined after 2003. Trends for severe pre-eclampsia also showed a modest birth cohort effect, with women born in the 1970s at increased risk. Compared with women born in 1955, the risk ratio for women born in 1970 was 1.2 (95% confidence interval 1.1 to 1.3). Similar patterns were also evident for mild pre-eclampsia, although attenuated. Changes in the population prevalence of obesity and smoking were associated with period and cohort trends in pre-eclampsia but did not explain the trends.

Conclusions: Rates of severe pre-eclampsia have been increasing in the United States and age-period-cohort effects all contribute to these trends. Although smoking and obesity have driven these trends, changes in the diagnostic criteria may have also contributed to the age-period-cohort effects. Health consequences of rising obesity rates in the United States underscore that efforts to reduce obesity may be beneficial to maternal and perinatal health.

Fig 1 Temporal changes in prevalence of pre-eclampsia: United States, 1980 to 2010

Fig 2 Age-period-cohort influences on trends in mild pre-eclampsia: United States, 1980 to 2010. Open circles refer to reference group for birth cohort and period. Adjusted risk ratio (red dot) for 1970 birth cohort (relative to reference cohort 1955) is 1.2 (95% confidence interval 1.1 to 1.2). Similarly, risk ratio (blue dot) for 2003 birth period (relative to reference period 1980) is 1.7 (95% confidence interval 1.6 to 1.8). Small hash marks on bottom x-axis pertain to knot locations for birth cohort, and hash marks on top axis refer to knot locations for period. Estimates for period effect are second order derivatives, indicating that slope of period effect for mild pre-eclampsia has been decelerating since 2003

Fig 3 Age-period-cohort influences on trends in severe pre-eclampsia: United States, 1980 to 2010. Open circles refer to reference group for birth cohort and period. Adjusted risk ratio (red dot) for 1970 birth cohort (relative to reference cohort 1955) is 1.2 (95% confidence interval 1.1 to 1.3). Similarly, risk ratio (blue dot) for 2003 birth period (relative to reference period 1980) is 6.7 (95% confidence interval 5.6 to 8.0). Small hash marks on bottom x axis pertain to knot locations for birth cohort, and hash marks on top axis refer to knot locations for period. Estimates for period effect are second order derivatives, indicating that slope of period effect for severe pre-eclampsia has been decelerating since 2003