These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Annual and sub-annual rhythms in human conception rates. I. Effective correction and use of public record LMP dates.
    Author: Boklage CE, Kirby CF, Zincone LH.
    Journal: Int J Fertil; 1992; 37(2):74-81. PubMed ID: 1349594.
    Abstract:
    Most studies of rhythms in human conception rates have used monthly total births back-dated 9 months. Such data are of little use for studying any pattern less than a few months in length. Even at that level, they are poor material for studying the possibility of altered conception rhythms in anomalous births. The high frequency of premature delivery in such births makes a simple 9-month offset simplistic and misleading. Dates of last normal menses (LMP) provide appropriate detail, but have generally been dismissed as unreliable. In a large public birth record dataset, we have identified a clear artifact of poor LMP recall, highly correlated with passage of time between conception and onset of prenatal care. The majority of the variation in daily LMP counts due to this recall artifact can be corrected statistically to yield population data suitable to more detailed analyses. All data on last menstrual period (LMP) for all births beyond 18-20 weeks' gestation between 1979-85 in North Carolina were summarized to demonstrate that most variation associated with inaccuracy of LMP dates in public datasets has a clear pattern which enables it to be corrected statistically to generate datasets acceptable to more detailed analyses. Total conceptions exhibited a clear annual rhythm with an autumnal rise followed by a sharp midwinter fall and an annual low in midsummer. The high and low rates varied by almost 20%. Single-day spikes recurred on the 1st, 5th, 10th, 15th, 20th, 25th, and the 28th days of the month throughout the 7 year average daily LMP counts. In fact, the 15th recurred the most often (Z score=almost 250 vs. 125 for day 1 [the next highest reported day]). The proportion of all LMP dates on these spike days increased as the length of pregnancy increased without prenatal care (p.0001). This explained 90% of the total variance in raw daily LMP counts and demonstrated that recall diminished with time. This correlation was used to reconstruct the data to more accurately reflect correct recall using ratios of expected/observed values for each day of the month by month prenatal care began group over the total dataset. The raw data in each day of the month by month prenatal care began group was multiplied by the corresponding ratio to construct the corrected dataset. The correction left artifactual excess LMP counts on and near major holidays and on the Nth day of the Nth month which were relatively insignificant compared with the major recall artifact variance. These reconstructions can be used to conduct additional analyses of rhythms with annual and subannual periods.
    [Abstract] [Full Text] [Related] [New Search]