General Obstetrics and Gynecology Obstetrics
Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination,☆☆

https://doi.org/10.1067/mob.2002.127601Get rights and content

Abstract

Objective: The purpose of this study was to evaluate the accuracy of algorithms for the assignment of gestational age with the use of the last menstrual period and early ultrasound information. Study Design: Gestational age estimates that are based on last menstrual period, ultrasound scanning, or their combination were compared among women who attended prenatal care clinics in central North Carolina (n = 3655) by an evaluation of digit preference in the last menstrual period dates and a comparison of mean gestational age, preterm and postterm categories with the use of κ statistics, difference between actual and expected delivery date, and birth weight among subgroups with discrepant assignments. Results: Last menstrual period reports show digit preference, assign gestation 2.8 days longer on average than ultrasound scanning, yield substantially more postterm births (12.1% vs 3.4%), and predict delivery among term births less accurately. Misclassification of births as postterm was more common in younger women, those of nonoptimal prepregnancy body weight, cigarette smokers, and women who reported last menstrual period using preferred dates of the month. Conclusion: Last menstrual period estimates of the duration of gestation are subject to both random error and a systematic tendency to overstate the duration of gestation, most likely because of delayed ovulation. (Am J Obstet Gynecol 2002;187:1660-6.)

Section snippets

Material and methods

The Pregnancy, Infection, and Nutrition (PIN) study was conducted at prenatal care clinics at the University of North Carolina (UNC) Hospitals and at Wake County Human Services and Wake Area Health Education Center. As described in detail elsewhere,7 we recruited women for a prospective cohort study with enrollment at 24 to 29 weeks of gestation. Given the clinic locations, most patients resided in Raleigh, Durham, Chapel Hill, Burlington, and surrounding smaller communities in central North

Results

Evaluation of digit preference for LMP dates (Fig 1) showed a notable tendency to recall the 15th of the month, followed by peaks for the 1st, 5th, and 20th days of the month.

. Digit preference for pregnancy dating with the use of the LMP and the percent of deviation from expected by the day of the month (n = 4485 women).

Accounting for months with fewer than 31 days, there were deficits in reports of the 27th to 31st of the month and for odd numbers adjacent to multiples of 5, such as the 9th,

Comment

These results add to the growing literature that indicates LMP alone is fallible as a method for dating conception on the basis of comparisons to ultrasound scanning.5, 9, 10 The errors in recall and reporting are apparent in the pattern of digit preference, larger standard deviation, and greater variability among term births. There appear to be two distinct problems with LMP-based estimates. First, there is a problem of inaccurate recall, reflected most explicitly in digit preference as found

Acknowledgements

We thank the project manager, Jude F. Williams, and the clinic site coordinators, Barbara Eucker and Anne Carter; the obstetrics clinics and staff for their cooperation (particularly Dr Thad McDonald, Dr Peter Morris, Ida Dawson, Dr Cathi Weatherly-Jones, Dr Juan Granados, and Sara Caviness); and the many obstetric care providers in these clinics who assisted in the conduct of the study.

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Supported by grants No. HD28684 and DA09096 from the National Institutes of Health; cooperative agreements S455-16/17, S0807-18, and S1099-19/19 through the Association of Schools of Public Health/Centers for Disease Control and Prevention and U64/CCU412273 through the Centers for Disease Control and Prevention; and funds from the Wake Area Health Education Center in Raleigh, NC.

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Reprint requests: David A. Savitz, PhD, Department of Epidemiology, CB #7435, University of North Carolina School of Public Health, Chapel Hill, NC 27599-7435. E-mail: [email protected]

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