The damage starts before the pregnancy test turns positive
The neural tube, the embryonic structure that becomes the brain and spinal cord, closes between days 21 and 28 after conception. Most women do not confirm a pregnancy until week 5 or 6. That gap is the clinical problem with folate deficiency. By the time a woman books her first antenatal appointment, the window for neural tube formation has already closed, with or without adequate folate on board.
