2.2. Household wealth index
We repeatedly assessed household wealth at enrollment of parent trial (<28 gestational weeks), mid-childhood and early adolescence, which was derived from principal component analysis for household assets and dwelling characteristics. The following items were included at pregnancy: (i) goods, bicycle, motor, orchard, radio, TV/VCD, refrigerator, washer, poultry, goat/sheep/pig, cattle/cow and car/tractor; (ii) characteristics of the house, house types (soil cave-dwelling, brick-cave dwelling, soil wall, brick/concrete wall, and apartment), materials for the floor, and availability of electricity, running water and household toilet. In addition to these, phone, computer, air conditioner and automatic water heater were included at mid-childhood and early adolescence. Briefly, household assets and dwelling characteristics were classified into Having/Yes and Not having/No. The household wealth index was priorly constructed and locally validated (