If venous thromboembolism, or VTE, goes unnoticed, it can be lethal. In fact, it's the leading cause of death for new mothers in developing nations. The condition starts as a blood clot in a deep vein (usually in the lower legs and thighs) but then it breaks off and travels through the blood to arteries in the lungs.

Now, VTE is a concern for women who have experienced a still birth or are either living with heart disease, varicose veins or inflammatory bowel disease, IBD, because they are likely to develop hazardous blood clots after giving birth, a new study claims.

"Preventative measures for VTE, such as a daily dose of heparin, may not be cost effective or safe and are therefore only recommended for women who are considered high risk," said Matthew Grainge, epidemiologist at the School of Community Health Sciences at The University of Nottingham. "However, there is currently inconsistency and disagreement over the factors which put women in that high-risk category and we hope that this research will provide clinicians with valuable new information."

The study is prompting change in how health care providers categorize and treat at-risk women during pregnancy, according to lead researchers. The study found that women who are obese, experiencing bleeding during pregnancy or labor in addition to having a premature birth or caesarian section are increasing their risk of a VTE.

The study gathered information using an online survey called GP Patient, on nearly 400,000 pregnancies for women between 14 and 44-years-old. GP Patient collects data on everything from patient records to hospital discharge forms to prescriptions.

The researchers considered risk factors in women such as varicose veins, high body mass index, or BMI, IBD and heart disease, among others, and compared how often these risk factors occurred between women who developed and those who did not develop VTE.

In the final data analysis, they determined new mothers who had a BMI over 30 had four times as great a chance of getting a VTE compared to those with a healthier BMI. In addition, women who experienced bleeding during pregnancy, had a premature birth, or a C-section doubled their chance of developing blood clots.

The chances were six times higher for women who had suffered still births.

"Our results may have important implications for the way that preventative measures for VTE are delivered in healthcare settings in developed countries," Grainge said. "We believe the strong association between stillbirths and premature births and VTE in particular is a finding of real importance which has received only limited attention to date. They are not currently incorporated in the guidelines for risk assessment for VTE and, if they were, then many cases associated with those risk factors could potentially be prevented."

Researchers at The University of Nottingham revealed their complete findings in the journal Blood.