Neural Tube Defects (NTDs) are one of the most severe congenital malformations. A study was conducted to determine whether supplementation with folic acid or a mixture of seven other vitamins (A, D, B1, B2, B6, C, and nicotinamide) around the time of conception could prevent neural tube defects. A total of 1817 women at high risk of having a pregnancy with a neural tube defect (because of a previous affected pregnancy) were allocated at random to one of four groups: 1) folic acid; 2) other vitamins; 3) both; 4) neither. 1195 had a completed pregnancy; 27 of these had a known neural tube defect, 6 in the folic acid groups and 21 in the two other groups. This resulted in a risk ratio= 0.28. What type of study design is this? a) Case-control b) Randomized controlled trial c) Prospective cohort d) Retrospective cohort

Neural Tube Defects (NTDs) are one of the most severe congenital malformations. A study was conducted to determine whether supplementation with folic acid or a mixture of seven other vitamins (A, D, B1, B2, B6, C, and nicotinamide) around the time of conception could prevent neural tube defects. A total of 1817 women at high risk of having a pregnancy with a neural tube defect (because of a previous affected pregnancy) were allocated at random to one of four groups: 1) folic acid; 2) other vitamins; 3) both; 4) neither. 1195 had a completed pregnancy; 27 of these had a known neural tube defect, 6 in the folic acid groups and 21 in the two other groups. This resulted in a risk ratio= 0.28. What type of study design is this? a) Case-control b) Randomized controlled trial c) Prospective cohort d) Retrospective cohort