Low birth weight (LBW; birth weight\<2500g) is an important predictor of mortality and morbidity in the neonatal period of early postnatal growth and growth during childhood. It is also associated with cognitive and behavioral development in the first years of life, health status during childhood, and adult health and human capital. As much as 16 % of all live births worldwide present a LBW, more than 90% being in low-income countries. Rates are particularly high in Asia and sub-Saharan countries. In Burkina Faso, it is estimated that 19 % of all live births in 1999-2005 were LBW.

In developing countries, most cases of LBW are attributed to intrauterine growth retardation (IUGR) rather than to preterm delivery. Factors interacting with fetal development are numerous. Among them maternal malnutrition, particularly energy and micronutrient deficiencies, and malaria during pregnancy are assumed to be major determinants of IUGR. Dietary surveys have consistently shown that multiple micronutrient deficiencies, rather than single deficiencies, are common. However, a number of randomized clinical trials in various countries have shown only a modest beneficial effect on fetal growth when providing multiple micronutrient supplements during pregnancy compared to folic acid and iron supplementation. It is expected that chronic energy deficiency during pregnancy could be hampering the full potential of the effect of multiple micronutrient supplementation. Therefore it is expected that incorporating multiple micronutrients in a food supplement (FS), that provides supplementary energy and protein, instead of multiple micronutrients (UNIMMAP), could have an effect of public health importance on fetal growth and its correlates. The UNIMMAP supplement composition, incorporated in the FS or given in the form of a tablet, was proposed by an expert committee organized by UNICEF, WHO and UNU for pregnancy and lactating women.

The study takes place in the health district of Houndé (south-west of Burkina Faso) in the surroundings of 2 health centers (12,000 inhabitants) from June 2003 to October 2006. Houndé is situated in a Sudano-Sahelian climate belt. The diet is essentially cereal-based. In 2004 and 2006, food consumption surveys estimated the average caloric intake during pregnancy at 8.6 MJ and 8.1 MJ during the postharvest and pre-harvest season respectively. Malaria transmission is permanent with seasonal variations. In 2002, the HIV prevalence among consulting pregnant women in the district was estimated at 2 %. The incidence of LBW in term infants was around 17% at the District Hospital in 2000-2001.

The recruitment of participants is community-based. During a preliminary census, houses in the study area are mapped and numbered and a unique identification code allocated to every woman of child-bearing age. Thirty locally trained home-visitors visit monthly every compound for early detection of pregnancy and referral to the health center for pregnancy test. Once the pregnancy is confirmed and after extensive explanation of the study purposes and procedures in Bwamu, Moré or Dioula, participants are asked to provide signed consent or thumbprints. There are no exclusion criteria other than planning to leave the area within the next 2 years.

This study is a randomized controlled trial, with directly observed supplement intake. Pregnant women are randomly assigned to receive daily either UNIMMAP tablet ( vitamin A 800µg, vitamin E 10 mg, vitamin D 5 µg, vitamin B1 1.4 mg, vitamin B2 1.4 mg, niacin 18 mg, vitamin B6 1.9 mg, vitamin B12 2.6 µg, folic acid 400 µg, vitamin C 70 mg, iron 30 mg, zinc 15 mg, copper 2 mg, selenium 65 µg, and iodine 150 µg) until delivery, or either a food supplement containing the UNIMMAP. The food supplement consists of 33% peanut butter, 32% heat-treated soy flour, 15% vegetable oil, 20% plain sugar and the UNIMMAP micronutrient cocktail in powdered form. Each participant allocated to the FS study group will receive 72g of FS daily which provides 1.56 MJ (372 kcal) of energy and 14.7g protein. The supplement is produced by a local women's association in collaboration with a food technologist, the micronutrients in the FS are dosed by a laboratory technician. UNIMMAP micronutrient tablets are manufactured by Scanpharm (Copenhagen, Denmark). A randomization scheme is generated by a computer program in permuted blocks of 4. Randomization numbers are sealed in opaque envelopes by administrative staff. At each inclusion, the consulting physician in the field opens the next sealed envelope and transmits the randomization number in case of MMN to a pharmacist managing for the packaging of drugs in individual plastic zip sachets containing 31 tablets. In case the randomization number shows allocation to the FS group, the responsible of the FS production site together with project staff, prepares a plastic bag containing 31 FS sachets.

Participants are also randomly assigned randomized to receive intermittent malaria prophylaxis by either two doses or more than two doses of combined sulfadoxine-pyrimethamine (a single dose represented 1500 mg sulfadoxine and 75mg pyrimethamine). The malaria component will be analysed separately.

In case of maternal illness, appropriate treatments are provided according to national guidelines. Severely anemic women (hemoglobin \< 70 g/L, without dyspnea) receive ferrous sulphate (200 mg) + folic acid (0.25 mg) twice daily, during 3 months whatever their allocation group. All participants also receive Albendazole 400 mg in the second and third trimester. In case of malaria episode despite the preventative treatment, quinine (300 mg, 3 times a day) is given during 5 days. Vitamin A (200.000 IU) is given to all women after delivery, in conformity with the national recommendations.