Despite modern obstetric and cardiac care, pregnancy in women with heart disease can be associated with significant complications to the health of the mother and child. Current risk estimates are primarily based on retrospective studies, a particular type of heart disease or examined cases at a specific hospital. This is the first large-scale study taking a prospective look at the frequency and predictors of pregnancy-related complications for a broad range of heart conditions.
"It is relatively uncommon for women who are pregnant to have heart disease. In most past studies looking at these conditions, heart disease in pregnant women usually comprises no more than 1 percent or 2 percent of the total pregnant population," says study author Samuel C. Siu, M.D., a cardiologist and associate professor at University of Toronto, Ontario. "Because it is so uncommon, the problem is more vulnerable to misinformation and sometimes lack of information."
This study developed a method of categorizing pregnant patients with heart disease into broad categories of risk - including low, medium and high - which will allow the appropriate care of these patients or the appropriate referral to specialized care centers, he says.
Siu and his colleagues studied 562 pregnant women with heart disease in 13 Canadian cardiac and obstetric teaching hospitals and recorded the outcomes of 599 pregnancies. (Some of the women were pregnant more than once during the five-year study.) Eighty-six percent of the women were between 18 and 35 years of age. Most of the women had a form of congenital heart disease (74 percent) - meaning she's had the condition since birth. Others had acquired heart disease (22 percent) or irregular heart rhythms called arrhythmias (4 percent).
The "good news" to come from the study, according to Siu, was that researchers found that the majority of women fared well through pregnancy. In 13 percent of the pregnancies, women experienced serious heart-related complications including fluid in the lungs, arrhythmia, stroke or death. Three women (1 percent) died from their heart complications.
Using this information, the researchers created a risk index to help physicians predict a woman's risk of having cardiac events or neonatal complications.
Researchers identified four maternal risk factors, or clusters of maternal characteristics, that could increase a woman's risk for heart complications. One is a prior cardiac event (including stroke, transient ischemic attack - which is known as a "mini-stroke" - or arrhythmia). The second factor is reduced oxygen level or cyanosis, which is characterized by tiredness, palpitations, difficulty breathing or chest pain brought on by ordinary physical activity. The third, left heart obstruction, is the presence of narrowing of the blood flow across the mitral and aortic valves. The fourth factor is systemic ventricular dysfunction which is a decreased pumping ability of the heart.
Each pregnancy was assigned one point for each predictor present. No pregnancy received more than three points. Researchers found that the estimated risk of a cardiac event in pregnant women with 0 points was 5 percent. The risk was 27 percent for one point and 75 percent for more than one point.
All three deaths occurred in pregnancies with more than one point.
The researchers conclude that the index can be used to accurately predict risk. In women at high risk (more than one point) for cardiac events, Siu suggests cardiac interventions should be considered before conception. These women should also be referred to a specialized hospital for ongoing care, he says. Those at low cardiac risk (0 points) should be able to safely deliver in a non-specialized hospital if there are no other risk factors specific to their underlying heart condition.
Complications with newborns, such as premature births and low-birth weights, occurred in 20 percent of the pregnancies. Seven newborns died and eight fetal deaths occurred. Characteristics that researchers determined would increase the risk of complications to the children were in part the same as their mother's, including low oxygen level and narrowed blood flow across the aortic and mitral valves. The researchers also found well-established risk factors for neonatal complications, including having multiple gestations (twins or triplets), smoking during pregnancy and use of blood thinners.
Other authors include Mathew Sermer, M.D.; Jack M. Colman, M.D.; A. Nanette Alvarez, M.D.; Lise-Andree Mercier, M.D.; Brian C. Morton, M.D.; Catherine M. Kells, M.D.; M. Lynn Bergin, M.D.; Marla C. Kiess, M.D.; Francois Marcotte, M.D.; Dylan A. Taylor, M.D.; Elaine P. Gordon, M.D.; John C. Spears, M.D.; James W. Tam, M.D.; Kofi S. Amankwah, M.D.; Jeffrey F. Smallhorn, M.D.; Dan Farine, M.D.; and Sheryll Sorensen, R.N; on behalf of the Cardiac Disease in Pregnancy (CARPREG) Investigators.
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