Comparison of gestational dating methods and implications for exposure-outcome associations: An example with PM2.5 and preterm birth

Kristen M. Rappazzo, Danelle T. Lobdell, Lynne C. Messer, Charles Poole, Julie L. Daniels

Research output: Contribution to journalArticle

Abstract

Objectives: Estimating gestational age is usually based on date of last menstrual period (LMP) or clinical estimation (CE); both approaches introduce potential bias. Differences in methods of estimation may lead to misclassification and inconsistencies in risk estimates, particularly if exposure assignment is also gestation-dependent. This paper examines a 'what-if' scenario in which alternative methods are used and attempts to elucidate how method choice affects observed results. Methods We constructed two 20-week gestational age cohorts of pregnancies between 2000 and 2005 (New Jersey, Pennsylvania, Ohio, USA) using live birth certificates: one defined preterm birth (PTB) status using CE and one using LMP. Within these, we estimated risk for 4 categories of preterm birth (PTBs per 106 pregnancies) and risk differences (RD (95% CIs)) associated with exposure to particulate matter (PM2.5). Results More births were classified preterm using LMP (16%) compared with CE (8%). RD divergences increased between cohorts as exposure period approached delivery. Among births between 28 and 31 weeks, week 7 PM2.5 exposure conveyed RDs of 44 (21 to 67) for CE and 50 (18 to 82) for LMP populations, while week 24 exposure conveyed RDs of 33 (11 to 56) and -20 (-50 to 10), respectively. Conclusions Different results from analyses restricted to births with both CE and LMP are most likely due to differences in dating methods rather than selection issues. Results are sensitive to choice of gestational age estimation, though degree of sensitivity can vary by exposure timing. When both outcome and exposure depend on estimate of gestational age, awareness of nuances in the method used for estimation is critical.

LanguageEnglish (US)
Pages138-143
Number of pages6
JournalOccupational and Environmental Medicine
Volume74
Issue number2
DOIs
StatePublished - Feb 1 2017

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Premature Birth
Gestational Age
Parturition
Pregnancy
Birth Certificates
Particulate Matter
Live Birth
Population

ASJC Scopus subject areas

  • Public Health, Environmental and Occupational Health

Cite this

Comparison of gestational dating methods and implications for exposure-outcome associations : An example with PM2.5 and preterm birth. / Rappazzo, Kristen M.; Lobdell, Danelle T.; Messer, Lynne C.; Poole, Charles; Daniels, Julie L.

In: Occupational and Environmental Medicine, Vol. 74, No. 2, 01.02.2017, p. 138-143.

Research output: Contribution to journalArticle

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