“…We used the following variables as covariates for mothers: maternal age (<25, 25–<30, 30–<35 or ≥35 years), pre-pregnancy body mass index asked during the first trimester (<18.5, 18.5–<25 or ≥25 kg/m 2 ), parity (primipara or multipara), history of allergy measured during the first trimester (yes or no), Kessler Psychological Distress Scale (K6) score (<5, 5–12, ≥13) [ 20 , 21 , 22 ], smoking status (never, former, or current), alcohol intake (never, former, or current), number of hours spent outdoors (<1, 1–<2, 2–<3 or ≥3 h), physical activity corresponding to over 10 min of walking a day (yes or no), quintile of folic acid intake measured using food frequency questionnaire (≤153, 154–203, 204–257, 258–337 or ≥338 µg) [ 23 , 24 ], marital status assessed during the first trimester (married, single, divorced, or widowed), highest educational level (≤12, >12–<16 or ≥16 years), employment status (yes or no), and annual household income (<4, 4–<6 or ≥6 million Japanese Yen). As covariates for dwelling environment, we used type of residence (wooden detached house, steel-frame detached house, wooden multiple dwelling house/apartment, steel-frame multiple dwelling house/apartment, or other), number of rooms in the house or apartment (≤2, 3, 4, 5 or ≥6), living room flooring material ( tatami [Japanese straw floor covering], carpet on tatami, wooden flooring/tiles, carpet on wooden flooring/tiles, or other), having a pet (yes or no) [ 18 ], usage of air purifiers (yes or no) [ 17 ], age of house or apartment building (<1, 1–<3, 3–<5, 5–<10, 10–<20 or ≥20 years, or unknown), house renovation or interior completion after conception (yes or no), and number of years living in the current place of residence (<1, 1–<3, 3–<5, 5–<10, 10–<20 or ≥20 years). These covariates comprise the general and socio-economic status and dwelling environment as well as variables that have potential impact on exposure and outcome.…”