Measurement time intervals and outcome measures
diarrhoea, nausea and vomiting
Because the appearance of certain morbidity symptoms is related to the duration of the pregnancy (e.g., nausea and vomiting often appear and peak during the first trimester, and disappear by the end of the second trimester (Lacasse & Bérard, For each measurement interval, we created two variables for each morbidity symptom. First, to calculate the period prevalence of each symptom, we created a binary variable with a value of 1 (if the woman reported the symptom for ≥1 day during the period in question) or 0 (if the woman never reported the symptom during the period in question). For example, for diarrhoea during the second trimester of pregnancy, the binary variable created had a value of 1 if the sum of the days the woman reported diarrhoea during the period was ≥1, and 0 if the sum was 0.Second, we calculated the percentage of days with each symptom during the period in question, based on the number of days of monitoring for each woman. For example, for diarrhoea during the second trimester of pregnancy, we summed the number of days the woman reported diarrhoea during the period, divided the sum by the number of days for which morbidity was monitored for the woman during that period, and multiplied the result by 100.