Heart attack in pregnancy

“Pregnant women 'four times as likely to have heart attack'”, reads the headline in The Daily Telegraph . As women are having children later in life, they “could potentially be increasing the risk of suffering heart problems”, the newspaper says.

The review on which the newspaper story is based did not look at the increase in risk of heart attack in women who are pregnant compared with those who are not, or whether the increasing age at which women are becoming pregnant is substantially affecting their risk of heart attack. Therefore, it is not possible to draw conclusions about these questions from this review.

Pregnant women should bear in mind that although heart attacks during or just after pregnancy are possible, their risk if they are otherwise healthy is very low, and they should not worry themselves unduly. Women can reduce their risk of heart attack by not smoking and by reducing the amount of saturated fat in their diet, and they should aim to do this regardless of whether they are pregnant or not.

Where did the story come from?

Drs Arie Roth and Uri Elkayam from university hospitals in Tel Aviv and Los Angeles wrote this paper. There were no specific sources of funding reported for this study. It was published in the peer-reviewed medical journal: the Journal of the American College of Cardiology .

What kind of scientific study was this?

This was a “state-of-the-art” paper, which aimed to review recent evidence about acute myocardial infarction (AMI, or heart attack) in pregnancy, and make suggestions about its diagnosis and treatment. This paper updated an earlier review by the authors, which they wrote over 10 years previously.

The researchers searched a database of scientific literature for articles about AMI during or after pregnancy, which had been published since their earlier review. They obtained these papers and translated any relevant non-English ones. They only included studies where a diagnosis of AMI was recorded based on chest pain, standard ECG (electrocardiograph) criteria, typical changes of certain markers (enzymes) in the blood or changes to heart tissue seen in women who died.

The authors identified 95 cases of AMI published between 1995 and December 2005. They also included another eight cases that they had treated or consulted on themselves. They compared the characteristics of women who had AMI just before birth (more than 24 hours before labour), during or just around birth (within 24 hours on either side of the delivery) or after the delivery (between 24 hours and three weeks after). They also compared the women in this review with the women they identified in their previous review. They then made recommendations about diagnosis and treatment of women with AMI based on their findings.

What were the results of the study?

The authors found that heart attacks can occur at any point during pregnancy. The women who had heart attacks ranged in age from 19 to 44. Most of them were over 30. About two thirds of the heart attacks during pregnancy occurred in women who had one or more previous pregnancies. One paper found that there was one case of heart attack for every 35,700 deliveries in California between 1991 and 2000, while another study found one case of heart attack for every 16,129 deliveries between 2000 and 2002 in the US.

The authors found that many of the women who had AMI had known risk factors, such as smoking (45%), unfavourable levels of cholesterol in the blood (24%), family history of AMI (22%), high blood pressure (15%) and diabetes (11%). These risk factors were more common in this group of women than in the women with AMI identified in the authors’ earlier review. This may have been because of a true increase in risk factors such as smoking, and because of better reporting of these risk factors.

Of the 103 women with heart attack, nine women died during the heart attack and two died during or after heart surgery. This death rate (11%) was lower than in their previous review (21%). Women who had heart attacks during the 24 hours before and after delivery were twice as likely to die (18%) compared with women who had a heart attack either before or after this period (9%). In 68 cases that occurred before delivery, the foetus died in six cases (9%) and in most cases this was associated with the death of the mother. The authors go on to discuss their findings about the diagnosis and treatment of heart attacks in pregnancy.

What interpretations did the researchers draw from these results?

The authors suggest that the apparent increase in the number of cases of heart attack in pregnancy may be due to improved methods of diagnosing heart attacks, or it may be a true increase in the number of cases. They also make some recommendations about diagnosis and management of heart attack in pregnancy, which take into account normal changes seen during pregnancy and the need to protect the safety of the foetus.

What does the NHS Knowledge Service make of this study? 

There a few points to consider when interpreting this study:

• The authors acknowledge that they will not have been able to identify all cases of AMI in pregnancy, as some of these will never have been reported in a medical journal. As such, the cases that were reported may not be representative of all cases of AMI in pregnancy.
• Although the authors have given the criteria they used for defining someone as having AMI, it is not clear whether these cases would be classified as AMIs according to current diagnostic criteria. For example, it is unclear from the report whether all of the criteria of “chest pain, standard electrocardiograph criteria, typical enzymatic changes” had to be fulfilled, or just some of them. It is also unclear which precise changes or definitions these were and whether they were clearly reported in the original case reports. There are other coronary syndromes similar to a classical heart attack and with similar prognostic indications. The occurrence of these events has not been covered by this research.  
• Taking both of the above points together, the number of cases of heart attack in pregnancy may not be accurate.
• The figures on the incidence of heart attack were from the US; it is not clear whether these figures are representative of what is seen in the UK or other countries.
• This review did not assess the increase in risk of heart attack in women who are pregnant compared with those who are not. The review also did not assess whether the increasing age at which women are becoming pregnant is substantially affecting their risk of heart attack. Therefore, it is not possible to draw conclusions about these questions from this article.
• The authors report that other studies have shown an increase in risk of three to four times the normal risk. Despite this possible increase, the risk of having a heart attack during pregnancy for an otherwise healthy woman of childbearing age is very low and should not concern pregnant women unduly. That pregnant woman do have slightly increased risk of cardiovascular diseases such as high blood pressure, blood clots and heart problems than similar non-pregnant women is a fact well-recognised by the medical profession.

Women can reduce their risk of heart attack by not smoking and by reducing the amount of saturated fat in their diet and they should aim to do this regardless of whether they are pregnant or not.