Child Tax Credit for Pregnant Moms Act of 2018 This bill amends the Internal Revenue Code, with respect to the child tax credit, to allow the credit to be used for an unborn child if the child is born and issued a Social Security number before the due date for the tax return (without regard to extensions) for the taxable year. The bill defines an "unborn child" as a member of the species homo sapiens, at any stage of development, who is carried in the womb. If a child is not taken into account for the credit for the year immediately preceding the year of the child's birth, the bill doubles the amount of the credit allowed for the year of the birth.