A new study published in the European Heart Journal has revealed that the risk of being admitted to the hospital with cardiovascular disease (CVD) is significantly higher in the year following childbirth for mothers of twins compared to those who have singletons. The findings suggest that twin pregnancies, especially those complicated by high blood pressure during pregnancy, pose a heightened risk for mothers in the postpartum period.
Led by Professor Cande Ananth, from the Department of Obstetrics, Gynecology, and Reproductive Sciences at Rutgers Robert Wood Johnson Medical School, this research highlights critical insights into the maternal risks that have often been overlooked in previous studies.
The Growing Trend of Twin Pregnancies
Over the past few decades, the incidence of twin pregnancies has risen globally, driven largely by the rise in fertility treatments and an increase in the average age of mothers. However, although previous studies have shown no long-term increase in cardiovascular risks for mothers of twins, these findings run counter to what clinicians frequently observe when caring for mothers in the postpartum period. As Professor Ananth notes, the rising twin pregnancy rate globally necessitates a closer look at how these pregnancies impact maternal health, particularly in the first year after birth when cardiovascular issues can be life-threatening.
“Given the unacceptably high rate of maternal mortality in the first year after birth due to cardiovascular disease, we wanted to examine whether twin pregnancies increase this risk,” said Ananth, acknowledging the potential urgency of the study.
Study Overview and Methodology
To investigate the relationship between twin pregnancies and cardiovascular risk, the researchers turned to a rich dataset from the US Nationwide Readmissions Database (NRD), which includes data from over 36 million hospital deliveries between 2010 and 2020. They divided the patients into four distinct groups based on the type of pregnancy (twin or singleton) and whether they had hypertensive diseases of pregnancy (HDP), such as gestational hypertension, pre-eclampsia, or eclampsia.
The four groups were:
- Mothers with twins and normal blood pressure during pregnancy
- Mothers with twins and hypertensive diseases of pregnancy
- Mothers with singletons and normal blood pressure
- Mothers with singletons and hypertensive diseases of pregnancy
For each group, the researchers calculated the rate of hospital readmissions due to cardiovascular diseases, including heart attack, heart failure, and stroke, within one year of childbirth. The results revealed some eye-opening findings.
Key Findings: Elevated Risks for Mothers of Twins
One of the most striking findings was that the rate of cardiovascular disease readmissions was significantly higher for mothers who had twin pregnancies than for those who had singleton pregnancies. Specifically, the readmission rate for cardiovascular events in mothers of twins was 1,105.4 per 100,000 deliveries, compared to 734.1 per 100,000 deliveries for those with singleton pregnancies.
For mothers with twins and normal blood pressure, the risk of hospitalization with cardiovascular disease was approximately twice as high compared to those with singleton pregnancies and normal blood pressure. For those who had twins and experienced high blood pressure during pregnancy, the risk was found to be more than eight times higher than for mothers with singleton pregnancies without hypertensive conditions.
These findings underscore a worrying trend: twin pregnancies, even in the absence of high blood pressure, pose a significant short-term cardiovascular risk.
The Role of Hypertension in Twin Pregnancies
However, when examining the impact of hypertensive diseases of pregnancy (HDP), the research found that mothers of twins with HDP faced an even more pronounced risk of cardiovascular complications. Hypertensive diseases of pregnancy include conditions such as pre-eclampsia, which is marked by high blood pressure and signs of organ damage, and eclampsia, a severe form of pre-eclampsia that can lead to seizures.
For those with HDP during a twin pregnancy, the risk of hospitalization for cardiovascular disease within the first year was dramatically elevated—by more than eight times—compared to mothers of singletons who did not experience high blood pressure.
Singleton Pregnancies with High Blood Pressure: A Longer-Term Risk
Interestingly, the study also revealed that while the short-term cardiovascular risks for mothers of twins were higher in the first year after childbirth, the long-term mortality risk seemed to be higher for mothers of singletons with high blood pressure conditions. This suggests that while mothers of twins may face an acute risk of cardiovascular complications in the immediate postpartum period, mothers with singleton pregnancies who have hypertensive conditions may be at greater risk over the long term, potentially due to pre-existing cardiovascular risk factors such as diabetes, obesity, or smoking.
The researchers, however, could not examine the role of other significant risk factors such as ethnicity, lifestyle choices, or pre-existing health conditions like obesity or smoking, which may have played a role in influencing cardiovascular outcomes. These variables were not consistently recorded in the data, making it difficult to fully account for their impact on the findings.
The Heart’s Strain During Twin Pregnancies
One of the lead authors of the study, Dr. Ruby Lin, a maternal-fetal medicine fellow at Rutgers Robert Wood Johnson Medical School, explained that the maternal heart is under significant strain during a twin pregnancy. “The maternal heart works harder for twin pregnancies than for singleton pregnancies, and it takes weeks for the maternal heart to return to its pre-pregnancy state,” she said.
This increased cardiovascular workload during pregnancy may be a key factor behind the elevated risk of cardiovascular events seen in the first year postpartum. Even mothers who do not experience high blood pressure during pregnancy may find themselves at increased risk due to the physiological demands placed on the heart by carrying multiples.
Implications for Care and Prevention
Given these findings, Dr. Lin emphasizes the need for heightened awareness among both patients and healthcare providers. “People with twin pregnancies should be aware of the short-term increase in cardiovascular disease complications in the first year after birth, even if they had a pregnancy that was not complicated by high blood pressure conditions, such as pre-eclampsia.”
For patients undergoing fertility treatments, particularly those who may be older or have other cardiovascular risk factors such as diabetes, obesity, or high blood pressure, it is essential that they are informed of the heightened risks associated with twin pregnancies. Health insurance companies and healthcare providers should also ensure that these mothers receive proper follow-up care up to one year after childbirth, as early intervention and monitoring could potentially mitigate these risks.
A Call for Postpartum Care and Collaboration
In an accompanying editorial, Dr. Katherine Economy from Brigham and Women’s Hospital, along with her colleagues, emphasized the critical importance of the fourth trimester, the period of 12 weeks after delivery, in shaping a mother’s long-term cardiovascular health. Given the high rate of maternal morbidity in the U.S., particularly related to cardiovascular events, Dr. Economy highlighted the urgent need for collaboration between obstetricians, cardiologists, and other specialists to address the crisis of maternal mortality.
“Greater understanding of risk factors for cardiovascular disease during pregnancy is of substantial interest, especially in light of current maternal morbidity rates in the U.S.,” Dr. Economy said. She further stressed the importance of improving postpartum care accessibility and quality, which could significantly reduce maternal complications and mortality rates.
Conclusion: A New Perspective on Twin Pregnancies
This study highlights an often-overlooked aspect of twin pregnancies—the short-term cardiovascular risks faced by mothers after childbirth. The findings call for a more nuanced approach to maternal care, with a focus on early detection, intervention, and follow-up care, particularly for mothers who have experienced twin pregnancies.
Given the increasing prevalence of twin pregnancies, especially those facilitated by fertility treatments, it is crucial for healthcare providers to be proactive in addressing the cardiovascular health of these mothers. By extending the period of postpartum monitoring and ensuring that mothers receive proper care in the year following childbirth, healthcare systems can better protect these mothers and ultimately improve maternal health outcomes.
As research continues to unravel the complexities of pregnancy-related cardiovascular risks, collaboration across medical specialties will be key to providing comprehensive care that supports both the immediate and long-term health of mothers.
Reference: Cande V. Ananth et al, Hospitalization for cardiovascular disease in the year after delivery of twin pregnancies, European Heart Journal (2025). DOI: 10.1093/eurheartj/ehaf003