Which vitamin is essential in early pregnancy to prevent nervous system defects such as spina bifida, which is characterized in the fetus by incomplete closing of the backbone and membranes around the spinal cord mastering biology?

The right answer is Vitamin B9 (folic acid).

Before and during pregnancy, supplementation with folic acid (or folate, or vitamin B9) is recommended. A deficiency in this vitamin can indeed be at the origin of serious malformations of the nervous system of the fetus such as spina bifida. The ideal is to start supplementation at the earliest because the nervous system develops in the first weeks of pregnancy.