This study sorts common variables used in dating pregnancy and ranks them according to their level of accuracy. The more accurate predictors, eg, LMP, should need no further corroboration during the course of pregnancy as long as the clinical course remains congruent with gestational length. Less accurate variables, eg, first fetal heart tones or fundal height need further confirmation in the absence of a useful menstrual history.
New research is presented on uterine height correlation with gestational age, within the context of related research. Since discrepant uterine size is the most commonly cited reason for ordering ultrasound during pregnancy, this variable was examined in terms of its correlation to gestational age in an effort to define the discrepancy so often cited. Results lead to the conclusion that there is a lack of research data justifying the practice of equating weeks of gestation and centimeters of fundal height. In fact, the data indicate a healthy range of variation and a general tendency for the uterine height to be less than weeks of gestation.
The length of the average term pregnancy is examined, with discussion of clinical implications. A management tool is offered to aid the clinician in deciding when further information is needed for a reliable data base. The usefulness of a singular EDD derived by any formula is discussed and the age old Naegele's rule is critically examined and compared to modern studies.