The data of the monitoring of the birth defects of the neural tube for 1985-2007 years from Crimean Republic Medical Genetic Center has been analyzed. The group of comparison: 127 cases of the neural tube defects The control group: 127 cases of birth of healthy children closest by the time and place of birth (for each case from comparison group). By the method of superposed epochs the weekly values of the heliogeophysical indices (Ap index of geomagnetic activity, Wolf Numbers--index of Solar activity, interplanetary magnetic field polarity) during the gametogenesis and embryo period of prenatal development The statistical significance of the values of heliogeophysical indices in the comparison and control groups was calculated using the statistical Wilcoxon criterion for the independent groups. It was founded that during 12-18 days of embryogenesis embryos with neural tube defects the increased geomagnetic activity is probable, comparing with the control group. Since the forming of the major part of the neural tube defects takes place during 2-3 weeks of embryo growth, the increase of geomagnetic activity during or before this stage may be one of the ecological risk factors for this pathology.