By the time the test reads positive, the deadline has often passed
The embryo's neural tube, the structure folic acid protects, is most vulnerable in the fourth week. About 121 million pregnancies a year are unintended.
What the study found
The neural tube closes in week four, often before a positive test
By the time a pregnancy test reads positive, the structure folic acid protects has usually already formed: the embryo's neural tube is most vulnerable in the fourth week. About 121 million pregnancies a year are unintended, which is how often that deadline passes unnoticed.
The caveat · 121 million is a model, not a count
The 121 million figure is a model, not a count, built from country surveys of uneven quality and published with an 80% uncertainty range of 112.8 to 131.5 million. It also says nothing about who was or was not taking folic acid. The week-four timing comes from a clinical reference chapter that gives no study for it.