The method was developed immediately following World War II by Willard F.
If urinary pregnancy test is negative similar findings may suggest submucosal fibroid or retained products of conception.
The earlier in pregnancy a scan is performed, the more accurate the age assignment from crown rump length.
The amount of the isotope in the object is compared to the amount of the isotope's decay products.
The object's approximate age can then be figured out using the known rate of decay of the isotope.
Each sample type has specific problems associated with its use for dating purposes, including contamination and special environmental effects.