Prenatal arsenic exposure and infant development and ultrasonogram, they were enrolled (n = 4,436). The women were randomized to two different prenatal interventions: They were first randomized to food consisting of a mix- ture of rice, lentils, molasses, and oil (two groups: early start or usual start) and then to three groups of micronutrient supplements from week 14 of gestation until delivery. The micronutrient groups received 60 mg iron + 400 µg folate, 30 mg iron + 400 µg folate, or 15 different vitamins and minerals containing iron and folate as well as iodine, zinc, sele- nium, copper, vitamins A, B1, B2, B3, B6, B12, C, D, and E. Further details of the dose have been published elsewhere (Tofail et al. 2008). Anthropometric measures of the women were taken on enrollment, and the infants’ weight, length, and head circumference were mea- sured within 72 hr of birth. Study subjects. There were 3,267 live births from the MINIMat study, and we selected a subsample (n = 2,853) comprising all pregnant women who delivered live-born singleton infants between May 2002 and December 2003 for developmental assess- ments at the age of 7 months. This provided sufficient power to allow examination of interactions among treatments with at least 1 complete year of births to cover seasonal variation. We assessed 74% (2,116) of chil- dren. Of the 737 children not tested, 298 (40%) were away from home at the time, 197 (27%) refused to be tested (probably because of fear of venipuncture), 121 (16%) had died, 59 (8%) had moved residence, and 62 (9%) were sick at the time of testing. Of the 2,116 tested infants, 1,799 had information on their mothers’ urinary arsenic in pregnancy and complete socioeconomic data collected in the MINIMat study and HDSS. Measurements. Biochemical measures. We based exposure assessment on arsenic in urine, which reflects total exposure to inor- ganic arsenic from all sources. Spot urine sam- ples were collected from the mothers at home at the time of pregnancy testing (gestational week 8, on average) and again at the clinic during the 30th gestational week. Urine was collected in cups and transferred to 24-mL acid-washed polyethylene containers. The urine samples were kept cold and transported to the hospital and deep-frozen to –70°C at the end of the day at the latest. They were subsequently transported (deep-frozen) to the Karolinska Institutet in Sweden for analysis of the total concentration of metabolites of inorganic arsenic, using the hydride genera- tion atomic absorption spectroscopy method (Vahter et al. 2006). We adjusted the arsenic concentrations for variation in urine dilu- tion by specific gravity, which we have found is less dependent on nutritional status and arsenic exposure than is creatinine adjustment (Nermell et al. 2008). Socioeconomic status. On enrollment, information about family structure, paren- tal characteristics, and socioeconomic con- ditions was collected by interview at home. The information included number of family assets (number owned from a list of posses- sions, e.g., television, radio, domestic animals, chairs, tables, beds, bicycle, rickshaw), deficits between income and expenditure (occasional or constant deficit in the previous month, yes/ no), number of children, and housing quality (floor, walls and/or roof made of mud, yes/no). Anthropometry. On enrollment, moth- ers’ weights were measured with SECA electronic scales (Seca GmbH, Hamburg, Germany), which are accurate to 100 g, and their heights were measured to the nearest 0.1 cm using a locally manufactured height stick. We calculated mothers’ body mass index (BMI; weight in kilograms/height in square meters). Infants’ birth weight was measured using beam balance scales that were precise to 10 g, and their lengths were measured with locally made length boards. Head circumfer- ence was measured to the nearest 1 mm using nonstretchable tape. At 7 months, the children were weighed and their lengths were measured at home. Research assistants were trained to carry out the anthropometric measurements according to standard procedures (WHO 1983). We converted the children’s heights and weights to standard scores using the WHO reference (WHO 2006). Cognitive and motor function. The Bayley Scales of Infant Development–II (BSID-II) (Bayley 1993) has two scales: the Psychomotor Development Index (PDI) and the Mental Development Index (MDI). It is the most commonly used infant test and has been used previously in Bangladesh (Black et al. 2004; Hamadani et al. 2002; Tofail et al. 2006) and showed good interobserver and test–retest reliabilities. We assessed the chil- dren’s motor development with the motor scale. In the first 2 years of age, the motor scale tends to be more sensitive to biologic dif- ferences such as the effects of iron supplemen- tation in iron-deficient infants (e.g., Lind et al. 2004; Moffatt et al. 1994) and protein energy supplementation in undernourished popula- tions (Pollitt and Oh 1994) than is the mental scale. In the present study, it was sensitive to differences between children whose mothers received either multiple micronutrient supple- mentation or iron and folate only in pregnancy (Tofail et al. 2008). It was also related to the child’s gestational age and current nutritional status and mothers’ nutritional status. We used two one-step means–end prob- lem-solving tests (PSTs), Support and Cover, to assess the infants’ cognitive development. The original procedures of the PSTs were described by Piaget (1955), but the conduct Environmental Health Perspectives • volume 117 | number 2 | February 2009 and scoring of the tests were designed by Willatts (1984, 1999). In these tests, infants manipulate an intermediary to retrieve a goal (a toy). The Support test involves placing a long cloth on a table in front of the child and then placing a toy out of the child’s reach at the farthest end of the cloth. The infant has to pull the cloth to retrieve the toy. In the Cover test, a toy is covered with a cloth while the infant is watching. The infant is then required to remove the cloth to retrieve the toy. We videotaped these procedures and scored them later. We gave four trials in both PSTs. We scored three behaviors in each trial: cloth behavior (the way the child handled the cloth), fixation behavior (the way the child fixed his or her vision on the toy), and toy behavior (the way the child grasped the toy). We scored each behavior on a three-point scale: 0 for no evidence of intention, 1 for possible/ambiguous intention, and 2 for clear evidence of intention. We summed the scores for each behavior over the four trials to give a total score ranging from 0 to 24. We chose the PSTs rather than the Bayley MDI, which is a global measure of develop- ment, because at this age the MDI does not correlate well with intelligence test scores in later childhood (Colombo 1993; Slater 1995). The PSTs measure specific cognitive func- tions, and early problem solving is related to IQ in later childhood (Slater 1995; Willatts 1997). The PSTs are sensitive to biologic and psychosocial differences in the first year of life, including birth weight in babies born at term (Meeks Gardner et al. 2003), supplementation with long-chain polyunsaturated fatty acids (Willatts et al. 1998a, 1998b), and the effects of 2 months of psychosocial intervention (Meeks Gardner et al. 2003). In the present sample, the test scores were sensitive to dif- ferences between infants whose mothers were supplemented with food early or later in preg- nancy, and we achieved good test–retest and interobserver reliabilities (Tofail et al. 2008). The tests are relatively easy to perform and can be readily scored from videotape, which facili- tates ongoing quality control in a large study. Therefore, if arsenic exposure in utero affects problem solving in infancy, we considered it likely that the effects would be detected. Behavior. We also used a modified ver- sion of Wolke’s behavior ratings (Wolke et al. 1990) to assess infant’s behavior dur- ing the assessments. This instrument has five ratings with nine-point scales: activity level (very still = 1 to overactive = 9), emotional tone (unhappy = 1 to radiates happiness = 9), response to examiner in first 5 min (avoiding = 1 to friendly and inviting = 9), cooperation with the test procedure (resists all suggestions = 1 to always complies = 9), and the amount of vocalization (very quiet = 1 to constant vocalization = 9) of infants. These ratings 289