Preeclampsia across pregnancies and associated risk factors: findings from a high‐risk US birth cohort 

1. Obesity was associated with recurrent preeclampsia among pregnant women during their first and subsequent pregnancies.

2. Diabetes mellitus, chronic hypertension and being overweight were found to be risk factors for incident and recurrent preeclampsia.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Preeclampsia is a disorder that affects approximately 8% of pregnancies in the United States. This complication involves hypertension and organ damage, characterized by proteinuria after 20 weeks of gestation. Preeclampsia is a risk factor for future diagnoses of cardiovascular disease and chronic hypertension. Previous studies have been limited as they have only assessed the impacts of obesity on preeclampsia risk primarily with Caucasian cohorts, despite the disorder carrying higher incidence and mortality in persons of colour.

To address these discrepancies, this prospective cohort study used an intersectional lens by including a racially and ethnically diverse cohort of pregnant women. The goal of this prospective cohort study was to understand the association between cardiometabolic risk factors and preeclampsia. Data was analyzed from the Boston Birth cohort and included 618 racially and ethnically diverse US mothers, including Black and Hispanic women. The study, being longitudinal in nature, followed each participant for two pregnancies. The first pregnancy being the “index” and the second being labelled as the “subsequent”.  Preeclampsia diagnosed only in the subsequent pregnancy was defined as an incident, as opposed to recurrent preeclampsia which occurred in both the index and subsequent pregnancies.  In order to longitudinally assess the mothers, the study looked to identify cardiometabolic risk factors before the index pregnancy, during the index pregnancy, between pregnancies (interpregnancy), and in subsequent pregnancies. Specifically, the cardiometabolic conditions being assessed included chronic diabetes, chronic hypertension and obesity.

Overall, of the 618 women included in the cohort, 78 had preeclampsia at the time of their index pregnancy while 540 did not. When comparing the women who never got preeclampsia to the women with index preeclampsia, the latter had higher interpregnancy cardiometabolic risk factors. Women with cardiometabolic conditions were at higher risk of preeclampsia. Also, women with higher BMIs were also associated with higher rates of both index and recurrent preeclampsia.  Furthermore, women with recurrent preeclampsia had higher rates of obesity compared to those without recurrent preeclampsia (30% vs 13%).

The study boasts reliable internal validity with its longitudinal design, accounting for time intervals between pregnancies, interpregnancy weight changes, and maternal health prior to index and subsequent pregnancies. Previous studies have focused on fixed time periods whereas this study was able to offer a more comprehensive temporal analysis. For example, women with interpregnancy hypertension were at much higher risk of incident preeclampsia (RR 6.1 (95% CI, 2.9-13)). The study did not find a statistically significant association between interpregnancy weight fluctuations and recurrent preeclampsia. However, this data was limited and previous studies have highlighted the importance of healthy weight loss. Future research may be warranted to better understand the clinical relevance of this time frame. Overall, this study is clinically relevant for reproductive health, maternal, and fetal health. Prevention interventions are key to reducing cardiometabolic conditions, such as diabetes and hypertension. Targeting behavioural changes to encourage weight loss, physical activity, and wellness among women before, during and after pregnancy may be beneficial in reducing the risk of preeclampsia.

Click to read the study in JAHA

Relevant Reading: Recurrent Preeclampsia: The Effect of Weight Change Between Pregnancies

In-Depth [prospective cohort]: This study analyzed data from the Boston Birth Cohort. Specifically, 618 mothers with 2 live births (Index birth and subsequent birth) were included. Mothers were assessed for cardiometabolic conditions such as chronic diabetes mellitus, obesity, chronic hypertension. Relative Risk was calculated for the association between each of these cardiometabolic risk factors and risk of preeclampsia. Women with pre index pregnancy obesity had twice the risk of incident preeclampsia compared to normal pre index pregnancy BMI (RR, 2.2 (95% CI, 4.5)). Women with pre index pregnancy cardiometabolic conditions were significantly more at risk for incident preeclampsia compared to women without risk factors (RR, 7.9 (95% CI, 4.1-15.3)).

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