Gizachew A Tessema1,2, M Luke Marinovich1, Siri E Håberg3, Mika Gissler4,5, Jonathan A Mayo6, Natasha Nassar7, Stephen Ball8, Ana Pilar Betrán9, Amanuel T Gebremedhin1, Nick de Klerk10, Maria C Magnus3,11,12, Cicely Marston13, Annette K Regan1,14, Gary M Shaw6, Amy M Padula15, Gavin Pereira1,3. 1. Curtin School of Population Health, Curtin University, Perth, Western Australia, Australia. 2. School of Public Health, University of Adelaide, Adelaide, South Australia, Australia. 3. Centre for Fertility and Health (CeFH), Norwegian Institute of Public Health, Oslo, Norway. 4. Information Services Department, Finnish Institute for Health and Welfare, Helsinki, Finland. 5. Department of Neurobiology, Care Sciences and Society, Karolinska Institute, Stockholm, Sweden. 6. Department of Pediatrics, March of Dimes Prematurity Research Center, Stanford University, Stanford, CA, United States of America. 7. Children's Hospital at Westmead Clinical School, Faculty of Medicine and Health, University of Sydney, New South Wales, Australia. 8. Curtin School of Nursing, Curtin University, Perth, Western Australia, Australia. 9. UNDP/UNFPA/UNICEF/WHO/World Bank Special Programme of Research, Development and Research Training in Human Reproduction, Department of Reproductive Health and Research, World Health Organization, Geneva, Switzerland. 10. Telethon Kids Institute, University of Western Australia, Subiaco, Western Australia, Australia. 11. MRC Integrative Epidemiology Unit at the University of Bristol, Bristol, United Kingdom. 12. Population Health Sciences, Bristol Medical School, Bristol, United Kingdom. 13. Faculty of Public Health and Policy, London School of Hygiene and Tropical Medicine, London, United Kingdom. 14. School of Public Health,Texas A&M University, College Station, Texas, United States of America. 15. Department of Obstetrics, Gynecology and Reproductive Sciences, University of California, San Francisco, CA, United States of America.
Abstract
BACKGROUND: Most evidence for interpregnancy interval (IPI) and adverse birth outcomes come from studies that are prone to incomplete control for confounders that vary between women. Comparing pregnancies to the same women can address this issue. METHODS: We conducted an international longitudinal cohort study of 5,521,211 births to 3,849,193 women from Australia (1980-2016), Finland (1987-2017), Norway (1980-2016) and the United States (California) (1991-2012). IPI was calculated based on the time difference between two dates-the date of birth of the first pregnancy and the date of conception of the next (index) pregnancy. We estimated associations between IPI and preterm birth (PTB), spontaneous PTB, and small-for-gestational age births (SGA) using logistic regression (between-women analyses). We also used conditional logistic regression comparing IPIs and birth outcomes in the same women (within-women analyses). Random effects meta-analysis was used to calculate pooled adjusted odds ratios (aOR). RESULTS: Compared to an IPI of 18-23 months, there was insufficient evidence for an association between IPI <6 months and overall PTB (aOR 1.08, 95% CI 0.99-1.18) and SGA (aOR 0.99, 95% CI 0.81-1.19), but increased odds of spontaneous PTB (aOR 1.38, 95% CI 1.21-1.57) in the within-women analysis. We observed elevated odds of all birth outcomes associated with IPI ≥60 months. In comparison, between-women analyses showed elevated odds of adverse birth outcomes for <12 month and >24 month IPIs. CONCLUSIONS: We found consistently elevated odds of adverse birth outcomes following long IPIs. IPI shorter than 6 months were associated with elevated risk of spontaneous PTB, but there was insufficient evidence for increased risk of other adverse birth outcomes. Current recommendations of waiting at least 24 months to conceive after a previous pregnancy, may be unnecessarily long in high-income countries.
BACKGROUND: Most evidence for interpregnancy interval (IPI) and adverse birth outcomes come from studies that are prone to incomplete control for confounders that vary between women. Comparing pregnancies to the same women can address this issue. METHODS: We conducted an international longitudinal cohort study of 5,521,211 births to 3,849,193 women from Australia (1980-2016), Finland (1987-2017), Norway (1980-2016) and the United States (California) (1991-2012). IPI was calculated based on the time difference between two dates-the date of birth of the first pregnancy and the date of conception of the next (index) pregnancy. We estimated associations between IPI and preterm birth (PTB), spontaneous PTB, and small-for-gestational age births (SGA) using logistic regression (between-women analyses). We also used conditional logistic regression comparing IPIs and birth outcomes in the same women (within-women analyses). Random effects meta-analysis was used to calculate pooled adjusted odds ratios (aOR). RESULTS: Compared to an IPI of 18-23 months, there was insufficient evidence for an association between IPI <6 months and overall PTB (aOR 1.08, 95% CI 0.99-1.18) and SGA (aOR 0.99, 95% CI 0.81-1.19), but increased odds of spontaneous PTB (aOR 1.38, 95% CI 1.21-1.57) in the within-women analysis. We observed elevated odds of all birth outcomes associated with IPI ≥60 months. In comparison, between-women analyses showed elevated odds of adverse birth outcomes for <12 month and >24 month IPIs. CONCLUSIONS: We found consistently elevated odds of adverse birth outcomes following long IPIs. IPI shorter than 6 months were associated with elevated risk of spontaneous PTB, but there was insufficient evidence for increased risk of other adverse birth outcomes. Current recommendations of waiting at least 24 months to conceive after a previous pregnancy, may be unnecessarily long in high-income countries.
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