2.3 Exposure assessment
The interview questionnaire contained items about physical exercise during pregnancy and each trimester, refers to the 1st trimester (0 to 12 weeks of gestation), the 2nd trimester (13 to 28 weeks of gestation), and the 3rd trimester (after 28 weeks of gestation). There were some questions about exercise on the questionnaire: 1) “Have you exercised during pregnancy? The exercise means any planned, organized, and repetitive physical activity.” 2) “What is your primary exercise patterns (walking, brisk walking, yoga/Pilates/maternity gymnastics, swimming, squat and others) during pregnancy?” For each trimester, take the 1st trimester as an example, 3) “How many times do you exercise per week during the 1st trimester?” 4) “How many hours do you exercise at a time?”.
Since Chinese pregnancy health guidelines do not involve exercise during pregnancy, the subjects’ activity was grouped according to the previous studies and existing guidelines[8-9,12]. Time spent on exercise were grouped as none and low (0-2.49h/week), moderate (2.5-7h/week), and high (>7h/week)[13]. One study defined “moderate exercise” as that requiring 4.5 METs (Metabolic Equivalent of Energy)[14]. So, energy expenditures were grouped as none and low (0-11.24 MET.h/week), moderate (11.25-31.5 MET.h/week), and high (>31.5 MET.h/week). The calculation of energy expenditure was based on the previous criterion[14].