Study finds increased risk of cardiovascular disease for mothers of twins

The risk of being admitted to the hospital with heart disease is twice as high the year after birth for mothers of twins compared to singleton births, according to research published in the European Heart Journal today (Monday). The risk is even higher in mothers of twins who had a high blood pressure condition during pregnancy.

The research was led by Professor Cande Ananth from the Department of obstetrics, gynecology, and reproductive sciences at Rutgers Robert Wood Johnson Medical School, New Jersey, USA.

The rate of twin pregnancies worldwide has risen in recent decades, driven by fertility treatments and older maternal ages. Previous studies have shown no long-term increased risk of cardiovascular disease when following people with twin pregnancies for decades after delivery. However, this is counterintuitive to what we observe clinically when caring for patients with twin pregnancies.

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.”

 Professor Cande Ananth, Department of obstetrics, gynecology, and reproductive sciences, Rutgers Robert Wood Johnson Medical School

The researchers studied data on 36 million hospital deliveries taken from the US Nationwide Readmissions Database of US hospitals from 2010 to 2020. They divided pregnant patients into four groups: those who had twins but normal blood pressure during pregnancy, those who had twins and hypertensive disease of pregnancy (high blood pressure conditions), those who had singleton pregnancies with normal blood pressure, and those who had singleton pregnancies with hypertensive disease of pregnancy.

Hypertensive disease of pregnancy includes gestational hypertension, pre-eclampsia, eclampsia, and superimposed pre-eclampsia.

For each group, researchers calculated the proportion of patients who were readmitted to the hospital within a year of childbirth with any type of cardiovascular disease, including heart attack, heart failure, or stroke.

Researchers found that the proportion of readmissions for cardiovascular disease within a year of giving birth was higher overall for those with twins (1,105.4 per 100,000 deliveries) than singleton pregnancies (734.1 per 100,000 deliveries).

Compared to singleton pregnancies with normal blood pressure, people with twins with normal blood pressure were around twice as likely to be hospitalised with cardiovascular disease. For those with twins with high blood pressure during pregnancy, the risk is more than eight times higher.

However, one year after birth, deaths from any cause, including heart disease, were higher among patients with singleton pregnancies who had high blood pressure conditions compared to patients with twins with high blood pressure conditions. This suggests that the risk to mothers of twins decreases in the longer term, while the mothers of singletons may have other pre-existing cardiovascular risk factors.

The researchers were not able to examine essential risk factors for cardiovascular disease, such as race/ethnicity, smoking, obesity, and drug use, because these were not consistently recorded in the database.

Dr Ruby Lin, a maternal-foetal medicine fellow at Rutgers Robert Wood Johnson Medical School and the study’s lead author, said: “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.

“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 having fertility treatments, especially for those with other cardiovascular risk factors, such as older age, obesity, diabetes, high blood pressure or heart disease, patients should be advised that twin pregnancies may increase cardiovascular disease complications in the short term.

“Given these higher risks, healthcare providers and health insurance companies should continue to provide follow-up for up to a year after birth for high-risk pregnancies such as twin pregnancies.”

In an accompanying editorial [2] Dr Katherine Economy from Brigham and Women’s Hospital, Boston, USA, and colleagues said: “Greater understanding of risk factors for cardiovascular disease (CVD) during pregnancy are of substantial interest in light of current maternal morbidity rates in the USA and data revealing that ∼33% of pregnancy-related deaths are attributable to cardiovascular events. 

“A particular knowledge gap in pregnancy and CVD centres around twin pregnancies. Twin pregnancies comprise 31 per 1000 births (3.1%) and roughly two-thirds are spontaneously conceived while the remaining third are conceived with assisted reproductive technologies (ART) such as in vitro fertilization (IVF) or ovulation induction therapies. 

“To address this gap in knowledge, in the current issue of the European Heart Journal, Lin et al. present new data from the Nationwide Readmissions Database (NRD) that highlight differences in 1 year risk of CVD hospitalizations and mortality between singleton and twin pregnancies with and without hypertensive diseases of pregnancy (HDP). 

“Remarkably, the authors observed significantly higher readmission rates for CVD events after a twin pregnancy compared with singletons, with an adjusted hazard ratio (HR) of 8.21 (95% confidence interval [CI] 7.48–9.01) and 1.95 (95% CI 1.75–2.17) among women with and without HDP, respectively. 

“We must embrace the fourth trimester (12 weeks after delivery) as a critical time period to make impactful changes that will influence long-term cardiovascular health. Collaboration among obstetricians, cardiologists, and other medical specialists is essential to address the crisis of maternal mortality and to reduce post-partum complications, including improving the accessibility and quality of post-partum care.”