Sunday, 3 November 2013

Pregnancy complications expose future disease risk

by Gráinne Long (MRC Epidemiology Unit, Cambridge, UK)
Short-listed for Access to Understanding 2013

Cardiovascular disease (CVD) describes any disease that affects the heart or blood vessels, and is currently the leading cause of death in women world-wide. Now complications during pregnancy can be used as an early indicator to identify women at high risk of future cardiovascular disease. Pregnancy provides a window into early adult female health, which can flag women at high risk of future ill health and may allow treatments to be targeted early to those who need it most. In this way CVD could be delayed or even prevented, suggest researchers who have looked at the relationship between pregnancy complications and future disease.

Shutterstock Image ID: 158482958 Copyright: Coffeemill

Earlier studies support a link between common complications during pregnancy and increased risk of CVD in later life. Women with a history of pregnancy related diabetes or pregnancy hypertension, pre-term delivery (i.e. before 37 weeks), or those bearing a low or high birth weight child, are more likely to develop future CVD. But whether these four complications independently predict risk of future disease, or whether one or a combination of pregnancy complications are better predictors of future health is unclear. For example, are a mother’s chances of developing future heart disease best predicted by a history of a specific complication, say pregnancy diabetes, or by a combination of complications, such as pregnancy diabetes and hypertension? This is important to figure out in order to establish whether similar pathways to CVD exist, which may provide opportunities to treat and stop disease.

Paths to disease
Debbie Lawlor and colleagues at the University of Bristol and University of Glasgow got around these pitfalls by studying the effects of all four pregnancy complications together on a range of CVD risk factors. CVD risk factors are known indicators of future increased CVD risk and include high blood glucose, insulin and fatty materials. Lawlor’s team looked at the pregnancy history of a large population of 3,416 mothers who also had key CVD risk factors measured an average of 18 years after pregnancy. Using statistical tools, a range of factors, or confounders, that could be alternative explanations for the link between pregnancy complications and CVD risk were also taken into account by Lawlor’s team; namely smoking, a mother’s education level and body mass. For example, smoking during pregnancy can increase CVD risk and also lead to a low birth weight child. So, taking smoking and other important confounders into account, allows true associations to be separated from those that are false.

Of the four pregnancy complications examined, pregnancy diabetes and hypertension were the best independent predictors of future CVD risk. Mothers with a history of pregnancy diabetes, were more likely to have raised blood glucose and insulin compared to healthy mothers some 18 years after pregnancy. Women with a history of pregnancy hypertension had a higher chance of having increased insulin and unhealthy fat (cholesterol and triglycerides) later in life, compared to their healthy counterparts. These associations did not change when statistical tools took account of all pregnancy complications and important confounders together, suggesting both pregnancy diabetes and hypertension are independent risk factors for CVD. The fact that different CVD risk factors associated with pregnancy diabetes as against hypertension, also suggests that there are different disease pathways linking these two pregnancy complications to CVD.

Human heart inside human x-ray body isolated on white background
Shutterstock Image ID:154171697 Copyright: ingridat

What about the effect of pregnancy complications on future CVD, rather than simply CVD risk factor levels? As the actual rate of CVD in this population was low, reflecting the relatively young age of the women, a well known ‘scoring system’ was used to estimate future CVD risk based on all the measured CVD risk factors combined. Using this approach Lawlor’s team found that, compared to healthy women, those suffering from pregnancy diabetes or pregnancy hypertension are 23% and 27% more likely to have a CVD event in the next 10 years, respectively. These findings held even when all pregnancy complications and confounders were taken into account together, further supporting a role for both complications as important predictors of future CVD risk.

Pregnant promises
“The stress test of pregnancy provides a glimpse into the otherwise silent early adult years in which chronic disease trajectories are set”, says Ellen Seely1 who specialises in cardiovascular diseases in women at Harvard. She says further investigation into the contribution of pregnancy complications to CVD is needed to fully understand, and benefit from, the early warning system pregnancy provides for predicting future health. Opportunities to screen during pregnancy and intervene in high risk women early to slow or stop disease progression could be on the horizon.

1Rich-Edwards, J. W., McElrath, T., McElrath, T., Karumanchi, A. and Seely, E. W. Breathing life into the lifecourse approach:Pregnancy history and cardiovascular disease in women. Hypertension (2010) 56(3), 331–334

This entry describes research published in the following article, selected by the Medical Research Council:

Associations of pregnancy complications with calculated CVD risk and cardiovascular risk factors in middle age: The Avon Longitudinal Study of Parents and Children
Abigail Fraser, Scott M. Nelson, Corrie Macdonald-Wallis, Lynne Cherry, Elaine Butler, Naveed Sattar, and Debbie A. Lawlor
Circulation (2012) 125(11), 1367–1380

Access to Understanding entrants are asked to write a plain English summary of a research article. For Access to Understanding 2013 there were 9 articles to choose from, selected by the Europe PMC funders.

The articles are all available from Europe PMC, are free to read and download, and were supported by one or more of the Europe PMC funders.

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