the calculator was developed at the request of physicians and health care professionals who wanted a quick method to compute the range of dates when the 1st trimester NT and serum test should be obtained, as well as a 2nd trimester QUAD test. These dates are calculated by either entering the known gestational age, the LMP, or the crown-rump length. The calculator also provides how many days are left before each test can no longer be obtained. The entrance criteria is based upon the requirements of the California Genetic Disease Branch but can be adapted to other geographical areas of the world.