Obesity in early pregnancy increases long-term risk of venous thromboembolism

By Dr. Priyom Bose, Ph.D.Sep 7 2023Reviewed by Lily Ramsey, LLM

A recent Scientific Reports study investigated the association between obesity in early pregnancy and long-term post-pregnancy risk of venous thromboembolism (VTE).

Study: Prepregnancy overweight and obesity and long-term risk of venous thromboembolism in women. Image Credit: FotoDuets/Shutterstock.com

Background

VTE is a medical condition when a blood clot forms in a vein. It is the third most common form of acute cardiovascular disease, after myocardial infarction and stroke.

There are two forms of VTE: pulmonary embolism (PE) and deep vein thrombosis (DVT).

Globally, around 10 million VTE cases are documented annually. The VTE prevalence rate is expected to significantly increase to 700 per 100,000 in individuals above 70 years of age due to the rise in life expectancy.  

In the last decade, the prevalence of obesity, being overweight, and severe obesity has significantly increased among youths. The World Health Organization (WHO) documented that the prevalence of obesity increased approximately three times between 1975 and 2016.

Although obesity has been identified as one of the prominent risk factors for VTE, this observation is based on a limited number of cases.

A prior study has indicated that obesity in men during early adulthood increases the risk of midlife VTE. However, this study failed to indicate whether there is a link between early-life obesity and the incidence of VTE in women.

About the study

The current study analyzed whether obesity during early pregnancy increases the long-term risk of VTE. All relevant data was obtained from the Swedish Medical Birth Registry (MBR), which has a high coverage.

Women between the ages of 18 and 45 years who gave birth to their first child between January 1, 1982, and December 31, 2014, were included.

All women included in this study were pregnant. The baseline weight indicated early pregnancy weight at weeks 8–12. During this period, only marginal weight is gained due to pregnancy.

One drawback of including only pregnant women in the cohort was that this group was relatively healthier than the average non-pregnant woman.

Study findings

This registry-based large-scale cohort study included 1,068,040 women as they fulfilled all eligibility criteria. The mean age of the study cohort was 27.5 years, and their mean BMI was 23.5 kg/m². The follow-up time of this study was 12.9 years.

A robust linear association between BMI and long-term post-pregnancy risk of VTE was observed in this study. During follow-up, 3,997 VTE cases were documented. The incidence rate of VTE per 100,000 person/year was estimated.

Out of 100,000 persons, 45.7 women with a BMI of 30–34.9 kg/m² and 61.1 women with a BMI of 35–59.9 kg/m² developed VTE.

In comparison, the incidence rate of VTE in women with low BMI, i.e., 20–22.4 kg/m², was significantly less, i.e., 22.1 in 100,000 women. Consistent with the findings of previous studies, this study indicates a significant long-term risk of VTE in the highly obese group. 

Interestingly, obesity was higher among young women at the time of VTE diagnosis than those with normal BMI. In contrast to the present study, a previous study with fewer participants and lower VTE prevalence indicated lower hazard ratios (HRs) linked to obesity.

Although the precise mechanism behind the increased risk of VTE in obese women is unclear, previous studies have hypothesized that it could be associated with physical factors, such as blood flow and adiposity.

Adipose tissue could be associated with the pro-thrombotic state found in obesity, which influences hemostasis, coagulation, and fibrinolysis. It must be noted that increased VTE risk due to obesity can be alleviated via proper weight management.

Conclusions

Since the inpatient registry was unavailable until 1987, some early VTE events may have missed the analysis. Another limitation of the study is that MBR only included women who gave birth to live babies and did not include pregnancy losses and stillborn children.

Therefore, the VTE risk in these groups was not analyzed. Taken together, this study might have underestimated the incidence of VTE. The lack of BMI data during follow-up was yet another limitation.

Furthermore, this study failed to determine the degree of weight loss that could reduce the risk of VTE incidence.

Despite the limitations, this study revealed that being overweight and obese increases the long-term risk of developing VTE compared to those with normal BMI.

Furthermore, young pregnant women with obesity are at a higher risk of developing VTE. Therefore, it is important to maintain a normal BMI throughout adulthood to reduce VTE risk and other unfavorable health outcomes.