An increase in the prevalence of constipation during pregnancy has been suggested to occur. We designed a prospective study to evaluate the prevalence of constipation during pregnancy and puerperium, to investigate possible associations with eating habits and lifestyle, and to evaluate the frequency of laxative use. A structured questionnaire was developed addressing demographics, obstetric characteristics, lifestyle, eating habits, variables required for the diagnosis of constipation, and laxative use to evaluate the prevalence of constipation during pregnancy and puerperium. The questionnaire was administered in the obstetric clinic in the first trimester of pregnancy, and by telephone in the second and third trimesters, and in the puerperal period. The prevalence of self-reported constipation in these time periods was 45.4, 37.1, 39.4, and 41.8%, respectively. Prevalence defined by the Rome II criteria for the same time periods was 29.6, 19, 21.8, and 24.7%. These values were similar to the data previously reported for the female population. Agreement between the self-reported and Rome II results was moderate. The self-reported criterion showed high sensitivity in all time periods, using the Rome II criterion as gold-standard. No factor was associated with variations in the prevalence of constipation during pregnancy, though an increase was recorded in the consumption of fruit, vegetables, fiber, and water. The prevalence of constipation during pregnancy and puerperium is similar to that recorded among the female population from the same geographic area.