The Impact of Computing Interpregnancy Intervals Without Accounting for Intervening Pregnancy Events

Background Meta‐analyses of observational studies have shown that women with a shorter interpregnancy interval (the time from delivery to start of a subsequent pregnancy) are more likely to experience adverse pregnancy outcomes, such as preterm delivery or small for gestational age birth, than women who space their births further apart. However, the studies used to inform these estimates have methodological shortcomings. Methods In this commentary, we summarise the discussions of an expert workgroup describing good practices for the design, analysis, and interpretation of observational studies of interpregnancy interval and adverse perinatal health outcomes. Results We argue that inferences drawn from research in this field will be improved by careful attention to elements such as: (a) refining the research question to clarify whether the goal is to estimate a causal effect vs describe patterns of association; (b) using directed acyclic graphs to represent potential causal networks and guide the analytic plan of studies seeking to estimate causal effects; (c) assessing how miscarriages and pregnancy terminations may have influenced interpregnancy interval classifications; (d) specifying how key factors such as previous pregnancy loss, pregnancy intention, and maternal socio‐economic position will be considered; and (e) examining if the association between interpregnancy interval and perinatal outcome differs by factors such as maternal age. Conclusion This commentary outlines the discussions of this recent expert workgroup, and describes several suggested principles for study design and analysis that could mitigate many potential sources of bias.

Section: Assess How Miscarriages and Pregnancy Terminations May Havmentioning

confidence: 99%

Good practices for the design, analysis, and interpretation of observational studies on birth spacing and perinatal health outcomes

Hutcheon

Moskosky

Ananth

et al. 2018

“…Information on intervening pregnancy losses can be determined by the “Date of Last Other Pregnancy Outcome (spontaneous or induced losses or ectopic pregnancies)” on the birth certificate; however, this information has been shown to have a high amount of missing data and documented poor data quality . While these distinctions may impact prevalence, a recent study showed this may be less of a concern for researchers interested in the effects of IPI on subsequent livebirth outcomes (e.g, preterm birth), regardless of intervening losses …”

Section: Measurement Of Interpregnancy Interval On the Birth Certificatementioning

confidence: 99%

Examining interpregnancy intervals and maternal and perinatal health outcomes using U.S. vital records: Important considerations for analysis and interpretation

Thoma

Silva

MacDorman

2018

Background Numerous studies use birth certificate data to examine the association between interpregnancy interval (IPI) and maternal and perinatal health outcomes. Substantive changes from the latest birth certificate revision have implications for examining this relationship. Methods We provide an overview of the National Vital Statistics System and recent changes to the national birth certificate data file, which have implications for assessing IPI and perinatal health outcomes. We describe the calculation of IPI using birth certificate information and related measurement issues. Missing IPI values by maternal age, race and education using 2016 birth certificate data were also compared. Finally, we review and summarise data quality studies of select covariate and outcome variables (sociodemographic, maternal health and health behaviours, and infant health) conducted after the most recent 2003 birth certificate revision. Results Substantive changes to data collection, dissemination and quality have occurred since the 2003 revision. These changes impact IPI measurement, trends and associations with perinatal health outcomes. Missing values of IPI were highest for older ages, lower education and non‐Hispanic black women. Minimal differences were found when comparing IPI using different gestational age measures. Recent data quality studies pointed to substantial variation in data quality by item and across states. Conclusion Future studies examining the association of IPI with maternal and perinatal data using vital records should consider these aspects of the data in their research plan, sensitivity analyses and interpretation of findings.

“…For the purposes of this meeting, interpregnancy interval was defined as the time between delivery of a livebirth and either the start of the next pregnancy or the start of the next pregnancy leading to a livebirth, depending on the data source (see Table for definitions of terms related to timing between pregnancies for an individual woman). The meeting did not focus on other types of birth and pregnancy intervals, such as interbirth intervals, postpregnancy loss interpregnancy intervals, or postabortion interpregnancy intervals. While these intervals may also be related to adverse pregnancy outcomes, studies using these measures were either methodologically inferior (eg interbirth intervals, which include the gestational length of the subsequent pregnancy) or beyond the scope of the meeting (eg postpregnancy loss or postabortion interpregnancy intervals, which may have unique associations with adverse health outcomes).…”

Section: Expert Work Group Meeting Scopementioning

confidence: 99%

“…The meeting did not focus on other types of birth and pregnancy intervals, 45,46 such as interbirth intervals, postpregnancy loss interpregnancy intervals, or postabortion interpregnancy intervals.…”

Section: E Xpert Work G Roup Mee Ting Scopementioning

confidence: 99%

Report of the Office of Population Affairs’ expert work group meeting on short birth spacing and adverse pregnancy outcomes: Methodological quality of existing studies and future directions for research

Ahrens

Hutcheon

Ananth

et al. 2018

Background The World Health Organization ( WHO ) recommends that women wait at least 24 months after a livebirth before attempting a subsequent pregnancy to reduce the risk of adverse maternal, perinatal, and infant health outcomes. However, the applicability of the WHO recommendations for women in the United States is unclear, as breast feeding, nutrition, maternal age at first birth, and total fertility rate differs substantially between the United States and the low‐ and middle‐resource countries upon which most of the evidence is based. Methods To inform guideline development for birth spacing specific to women in the United States, the Office of Population Affairs ( OPA ) convened an expert work group meeting in Washington, DC , on 14‐15 September 2017 among reproductive, perinatal, paediatric, social, and public health epidemiologists; obstetrician‐gynaecologists; biostatisticians; and experts in evidence synthesis related to women's health. Results Presentations and discussion topics included the methodological quality of existing studies, evaluation of the evidence for causal effects of short interpregnancy intervals on adverse perinatal and maternal health outcomes, good practices for future research, and identification of research gaps and priorities for future work. Conclusions This report provides an overview of the presentations, discussions, and conclusions from the expert work group meeting.