Background: As more women with congenital heart disease (CHD) are reaching childbearing age, it becomes more common for their symptoms to be evaluated during pregnancy. However, pregnancy-related symptoms are similar to those caused by heart disease. This study investigated the prevalence of factors associated with symptoms during pregnancy in women with CHD. Methods: The national birth register was searched for primiparous women with CHD who were registered in the national quality register for patients with CHD. Results: Symptoms during the third trimester were reported in 104 of 465 evaluated women. The most common symptom was palpitations followed by dyspnea. Factors associated with symptoms were tested in a univariable model; higher NYHA classification (>1) (OR 11.3, 95%CI 5.5-23.2), low physical activity (<= 3 h/week) (OR 2.1 95%CI 1.3-3.6) and educational level <= 12 years (OR 1.9 95%CI 1.2-3.0) were associated with having symptoms. In multivariable analysis, low physical activity level (OR 2.4 95%CI 1.2-5.0) and higher NYHA class (OR 11.3 95%CI 5.0-25.6) remained associated with symptoms during pregnancy. There were no cases with new onset of impaired systemic ventricular function during pregnancy. Conclusion: Symptoms during pregnancy are common in women with CHD but are often already present before pregnancy. Because ordinary symptoms during pregnancy often overlap with symptoms of heart disease, it is important to know if symptoms were present before pregnancy and if they became worse during pregnancy. These results should be included in pre-pregnancy counselling and considered in the monitoring during pregnancy.