Assessing number‐specific error in the recall of onset of last menstrual period

Abstract

The goal of this investigation was to determine whether women who did not report preferred numbers for their last menstrual period (LMP) may be a group of women who are particularly careful in keeping track of their menstrual cycles and therefore have more accurate LMP dating--based on a comparison with ultrasound examinations. We also sought to estimate the frequency with which preferred numbers are reported in different sources of data and for different subgroups of women. First, we examined the 1987 California birth certificates in which LMP was collected at the time of birth (n = 504853). We also examined the records of 43880 women participating in the California Alpha-fetoprotein (AFP) Screening Program between 1986 and 1987, for whom gestational ages based on both early ultrasound examination and LMP were collected before 20 weeks of gestation. In the 1987 California birth certificates, seven numbers--1, 5, 10, 15, 20, 25 and 28--were recorded more frequently than expected. An estimated 12.9% of these records had preferred numbers. The most frequently recorded number was 15, occurring 2.5 times more often than expected (P < 0.01). In the data of the AFP Screening Program, the same seven numbers were preferred, and approximately 7.9% of records were affected by number preference. Comparisons with measurements of gestational age based on ultrasound demonstrated that LMP-based gestational ages in which non-preferred numbers are reported for the LMP are slightly more accurate than those in which preferred numbers are reported (P < 0.01). In most cases, number preference appears to introduce small errors into measurements of gestational age, probably as a result of rounding. Thus, the effect of number preference may be primarily of interest to research studies in which small errors in the measurement of gestational age will have a significant impact on findings.

Methods of gestational age assessment influence the observed association between antiretroviral therapy exposure, preterm delivery, and small-for-gestational age infants: a prospective study in Cape Town, South Africa

“…This includes high level of injectable contraception use, 30 long-term use of which affects return to menses and fertility, limiting LMP reliability. 31 Additionally younger, primigravid women and women with lower educational levels are more likely to misreport LMP. 12,28 Since HIV-uninfected women were more likely to be younger and primigravid it is possible they misreported their LMP more than HIV-infected women, which could explain why the expected association by HIV status was not observed with LMP-GA.…”

Are anesthesia start and end times randomly distributed? The influence of electronic records

“…A review of reported last menstrual periods collected in California in the 1980s suggested that the numbers 1, 5, 10, 15, 20, 25, and 28 were the most “preferred” recorded times, each occurring more frequently than would otherwise be expected due to chance. Furthermore, when compared with ultrasound estimates of gestational ages, last menstrual periods recorded as a nonpreferred value lead to more accurate gestational age estimates than those last menstrual periods estimated using “preferred” times [16]. Similar to our trend of increasing clustering across time, the proportion of birth weights with zero recorded for the end digit increased as the birth weight itself increased [17].…”

Determinação da idade gestacional com base em informações do estudo Nascer no Brasil

“…The proper entry of many numbers and recall biases from the women 9,10 , in a setting of many unplanned pregnancies certainly aid to that. This pattern was seen in both types of birthcare payment (public and private); the latest composed of women with higher socioeconomic level.…”

“…LMP-based gestational age is fallible in many cases, such as individual variation of the duration of the menstrual cycle, implantation bleeding, and, particularly, recall biases 9,10 . In Brazil, a high proportion of the population has low schooling -a feature associated to worse quality of information about LMP 5,6 .…”