After receiving a full explanation on the purpose of the study, the women were given a self-administered structured questionnaire to ascertain their individual baseline characteristics. The table of food intake recommended for pregnant women published in an antenatal care handbook provided by the Ministry of Public Health, Thailand was used for guidance of food items required. The six food groups including rice, vegetable,meat, fruit, fat and milk were listed. The units for measuring the amount of each food was recorded as ladles for rice and vegetables, portions for fruit, tablespoons for meat, tea-spoons for fat and glasses for milk. Photographs of the types and amounts of foods were shown to the women to improve estimation of portion size.
The subjects were requested to recall their average daily intake for breakfast, lunch, dinner and supper over the previous two weeks for all food groups and the amount eaten using the standard units mentioned above. If the consumed food was not in the list, then that kind of
food was converted into an equivalent amount of the same food type. For example, noodles were converted into rice equivalent. Total food intake regarding types, amount and frequency were calculated into weight of macronutrient and micronutrient using the modified Food Nutrient Conversion Table endorsed by the Nutrition Division of the Ministry of Public Health, Thailand [17].