Mothers with preterm delivery appear to be more likely in their future to develop a stroke, both haemorrhagic and ischemic. The research, recently presented in the journal Circulation, showed that this increased risk for stroke was independent of other confounding factors and remained substantially elevated throughout life for at least 40 years.
Stroke in women
Stroke is the second leading cause in terms of years of life lost to disability worldwide, and the prevalence of stroke in women is expected to surge rapidly, due to the increase in the average age of the global female population.
Moreover, strokes that occur in women usually tend to be more severe and more frequently have a fatal outcome. The influence of certain stroke risk factors, including diabetes mellitus and atrial fibrillation, is stronger in women.
Ischemic or hemorrhagic stroke can be devastating complications during pregnancy and the puerperium. This event is estimated to occur in approximately 30 out of 100,000 pregnancies, but in high-risk women, such as those with preeclampsia, the incidence of both stroke subtypes, combined, is up to 6 times higher than in women with pregnancy without this disorder. A risk that is maintained even for decades after pregnancy.
However, until now it had never been clearly highlighted what the risk of stroke is in the woman with preterm birth. Considering that preterm birth occurs in about 10% of pregnancies, it seems to be clear how relevant a possible link between this event and the risk of developing stroke can be.
Over two million Swedish women
In this new study, the researchers evaluated more than two million Swedish women on the Swedish Medical Birth Register, a national health registry that has collected prenatal and birth information from nearly all births since 1973.
The women were then divided into 6 groups, based on the number of weeks of pregnancy completed: extremely preterm (22-27 weeks), very preterm (28-33 weeks), late preterm (34-36 weeks), early term (37 -38 weeks), term (39-41 weeks) and post-term (≥42 weeks). Women included in the term group were represented controls.
The primary endpoint was stroke of any type, while the secondary endpoint was the separate assessment of ischemic and hemorrhagic strokes. Their diagnosis was taken from the Swedish Hospital Register. Analyzes were corrected for the most common genetic or environmental confounders.
The risk of stroke in women with preterm delivery
The results of the study showed that women with premature delivery had more frequently: less than 20 years of age, a low level of education, a smoking habit, a high prenatal body mass index, a preeclampsia and diabetes.
During the follow-up, a stroke occurred in 1.7% of the women evaluated. The median age at first delivery was 27 years, while the mean age at stroke diagnosis was 55 years.
Considering the entire duration of follow-up, which lasted up to 43 years after the first delivery, the risk indices for stroke in the groups of women with preterm, extremely preterm or early birth were 1.42, 1.77 e 1.16 respectively. If the pregnancy was prolonged by an extra week, this corresponded to an average risk reduction of 5%.
Looking at the first 10 years after delivery, the risk index for stroke came to 2.81 for preterm delivery, 2.07 for extremely preterm delivery, 2.07 for very preterm delivery, and 1. 38 for the late preterm.
Looking at the evolution over time of the risk of stroke, it is clearly showed that in the first two follow-up periods (less than 10 years, between 10 and 20 years) the group of women at the highest risk are those whose delivery is between the twenty-second and twenty-seventh week of pregnancy. These are followed by women with a “very preterm” birth (week 28-33). In these groups, the risk of having a stroke varies from about double to almost three times that of women who give term delivery.
In the subsequent follow-up periods, ranging from over 20 years up to 43 years, the risk is reduced and becomes similar in all groups of women considered in the study, but remains substantial, hovering around maximum values of 1.5- 1.6.
The highest risk of stroke for women with preterm delivery concerned both hemorrhagic and ischemic ones but was more strongly associated with the latter (up to 43 years: 1.31 versus 1.54).
A risk that persists for many years
This new research reveals a considerable risk of stroke in women with preterm delivery, a risk that remains high for many years. Considering that an early termination of the pregnancy period is not so infrequent, it can be understood how strong the impact of these data is on the clinical management of the female population of childbearing age.
It is striking how high the risk is in the first twenty years after childbirth, when it is almost three times higher than in women who have had a full-term birth. However, the persistence of this high risk over time is also striking, even if it is progressively decreasing. Preterm delivery appears to be an event that marks the risk of cerebrovascular events for life.
The authors try to explain the results of their study with different hypotheses. First, they note that preeclampsia and other hypertensive disorders during pregnancy are common causes of preterm delivery and are associated with the subsequent development of stable hypertension over time. Hypertension in turn is a known risk factor for stroke.
The other aspect considered is the alteration of inflammatory processes in case of preterm delivery. In fact, in this occurrence, proinflammatory substances are secreted, such as interleukin-1 and interleukin-6. Factors that play a key role in the development of alterations in the vessel walls, favoring the development and progression of atherosclerosis, another known risk factor for stroke.
Preterm delivery in the evaluation of cardiovascular risk
Whatever the mechanism responsible for the increased risk of stroke in the case of preterm birth, it is certain that its occurrence must be considered as an important alarm in terms of cardiovascular prevention. So much that the authors suggest including habitually reproductive history, and in particular the occurrence of preterm delivery, in the screening for cardiovascular risk in women.
Considering the findings of the study, a question inevitably arises: can preterm delivery also represent a risk factor for myocardial infarction? Considered the close link between stroke and myocardial infarction, in terms of predisposing factors and pathophysiological mechanisms it cannot be excluded. It is also clear that new research will be needed to demonstrate this link, which will explore more extensively the effects of alterations induced by preterm birth on cardiovascular system.
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