Estimates of Gestational Age

James D. Knoke, PhD; Robert J. Sokol, MD
JAMA. 1989;261(16):2329. doi:10.1001/jama.1989.03420160053017.
Text Size: A A A
Published online

To the Editor. —  The article by Kramer et al1 reaffirms the poor quality of estimates of gestational age afforded by dating of the last normal menstrual period (LNMP). The authors express surprise that the magnitude of the bias toward the mean of such estimates increases the further the LNMP estimate differs from the mean of the estimates. This should not come as a surprise. In fact, it can be anticipated from probabilistic considerations without collecting any data.To illustrate why bias toward the mean increasing as distance from the mean increases could be anticipated, consider the following hypothetical simplification. Suppose that all gestational ages at delivery are 39 weeks, but that the LNMP estimate has a distribution ranging from 36 to 42 weeks. Then consider a plot, like the figure on page 3307 of the article by Kramer et al, of the difference between the LNMP estimate


Sign In to Access Full Content

Don't have Access?

Register and get free email Table of Contents alerts, saved searches, PowerPoint downloads, CME quizzes, and more

Subscribe for full-text access to content from 1998 forward and a host of useful features

Activate your current subscription (AMA members and current subscribers)

Purchase Online Access to this article for 24 hours




Meets CME requirements for:
Browse CME for all U.S. States
Accreditation Information
The American Medical Association is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. The AMA designates this journal-based CME activity for a maximum of 1 AMA PRA Category 1 CreditTM per course. Physicians should claim only the credit commensurate with the extent of their participation in the activity. Physicians who complete the CME course and score at least 80% correct on the quiz are eligible for AMA PRA Category 1 CreditTM.
Note: You must get at least of the answers correct to pass this quiz.
You have not filled in all the answers to complete this quiz
The following questions were not answered:
Sorry, you have unsuccessfully completed this CME quiz with a score of
The following questions were not answered correctly:
Commitment to Change (optional):
Indicate what change(s) you will implement in your practice, if any, based on this CME course.
Your quiz results:
The filled radio buttons indicate your responses. The preferred responses are highlighted
For CME Course: A Proposed Model for Initial Assessment and Management of Acute Heart Failure Syndromes
Indicate what changes(s) you will implement in your practice, if any, based on this CME course.
Citing articles are presented as examples only. In non-demo SCM6 implementation, integration with CrossRef’s "Cited By" API will populate this tab (http://www.crossref.org/citedby.html).


Some tools below are only available to our subscribers or users with an online account.

Sign In to Access Full Content

Related Content

Customize your page view by dragging & repositioning the boxes below.