{"doi":"10.1093/ije/dyab168.176","title":"1273Confounding in the association between pregnancy complications and subsequent preterm birth","abstract":"<jats:title>Abstract</jats:title>\n               <jats:sec>\n                  <jats:title>Background</jats:title>\n                  <jats:p>Underlying causal mechanisms that persist from pregnancy to pregnancy have potential to explain recurrence of pregnancy complications. We aimed to estimate the degree of confounding necessary to explain these associations.</jats:p>\n               </jats:sec>\n               <jats:sec>\n                  <jats:title>Methods</jats:title>\n                  <jats:p>This was a retrospective cohort study of women (n = 124,936) giving birth to their first and second singleton children in Western Australia 1998-2015, identified from the Midwives’ Notifications System. The investigated pregnancy complications were preterm birth (&amp;lt;37 gestational weeks), pre-eclampsia, placental abruption, small-for-gestational-age and perinatal death. Adjusted relative risks (RR) and confidence intervals (CI) were reported. We simulated maternal obesity and derived E-values, a method to determine the magnitude of unmeasured confounding.</jats:p>\n               </jats:sec>\n               <jats:sec>\n                  <jats:title>Results</jats:title>\n                  <jats:p>Complications in first pregnancy were associated with higher risk of preterm birth in second pregnancy. RR’s were significantly higher when the complication was recurrent. For the association between pre-eclampsia at first term birth and subsequent preterm birth, the RR increased from 1.2 (95% CI 1.05-1.41) to 11.9 (95% CI 9.52-11.49) when the complication reoccurred. E-values were 1.73 and 23.22 respectfully. Relative risks did not change after adjustment for maternal obesity.</jats:p>\n               </jats:sec>\n               <jats:sec>\n                  <jats:title>Conclusions</jats:title>\n                  <jats:p>The strong associations between pregnancy complications and preterm birth support the assumption of shared underlying causes that persist from pregnancy to pregnancy. High E-values suggest that recurrent confounding is unlikely, as any such unmeasured confounder would have to be uncharacteristically large.</jats:p>\n               </jats:sec>\n               <jats:sec>\n                  <jats:title>Key messages</jats:title>\n                  <jats:p>Well-established single confounders cannot explain away the strong associations between complications in first pregnancy and a subsequent preterm birth.</jats:p>\n               </jats:sec>","journal":"International Journal of Epidemiology","year":2021,"id":628254,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":0,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":null,"is_data_producer":false,"deposit_databanks":null,"is_oa":false,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":null,"fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":61390,"name":"Gizachew Assefa Tessema","orcid":"0000-0002-4784-8151","position":1,"is_corresponding":false},{"id":400540,"name":"Gavin Pereira","orcid":"0000-0002-9271-9578","position":2,"is_corresponding":false},{"id":1626531,"name":"Jennifer Dunne","orcid":null,"position":0,"is_corresponding":false}],"reference_count":0,"raw_metadata":{"has_enrichment":true,"resolved":true,"title":"1273Confounding in the association between pregnancy complications and subsequent preterm birth","abstract":"<jats:title>Abstract</jats:title>\n               <jats:sec>\n                  <jats:title>Background</jats:title>\n                  <jats:p>Underlying causal mechanisms that persist from pregnancy to pregnancy have potential to explain recurrence of pregnancy complications. We aimed to estimate the degree of confounding necessary to explain these associations.</jats:p>\n               </jats:sec>\n               <jats:sec>\n                  <jats:title>Methods</jats:title>\n                  <jats:p>This was a retrospective cohort study of women (n = 124,936) giving birth to their first and second singleton children in Western Australia 1998-2015, identified from the Midwives’ Notifications System. The investigated pregnancy complications were preterm birth (&amp;lt;37 gestational weeks), pre-eclampsia, placental abruption, small-for-gestational-age and perinatal death. Adjusted relative risks (RR) and confidence intervals (CI) were reported. We simulated maternal obesity and derived E-values, a method to determine the magnitude of unmeasured confounding.</jats:p>\n               </jats:sec>\n               <jats:sec>\n                  <jats:title>Results</jats:title>\n                  <jats:p>Complications in first pregnancy were associated with higher risk of preterm birth in second pregnancy. RR’s were significantly higher when the complication was recurrent. For the association between pre-eclampsia at first term birth and subsequent preterm birth, the RR increased from 1.2 (95% CI 1.05-1.41) to 11.9 (95% CI 9.52-11.49) when the complication reoccurred. E-values were 1.73 and 23.22 respectfully. Relative risks did not change after adjustment for maternal obesity.</jats:p>\n               </jats:sec>\n               <jats:sec>\n                  <jats:title>Conclusions</jats:title>\n                  <jats:p>The strong associations between pregnancy complications and preterm birth support the assumption of shared underlying causes that persist from pregnancy to pregnancy. High E-values suggest that recurrent confounding is unlikely, as any such unmeasured confounder would have to be uncharacteristically large.</jats:p>\n               </jats:sec>\n               <jats:sec>\n                  <jats:title>Key messages</jats:title>\n                  <jats:p>Well-established single confounders cannot explain away the strong associations between complications in first pregnancy and a subsequent preterm birth.</jats:p>\n               </jats:sec>","is_dataset_classified":null,"base_score":0.0,"endowment":0.0,"datacite_reuse_total":0,"file_count":0,"downloads":0,"views":0,"has_version_chain":false,"is_dataset":false,"is_oa":false,"pmid":"19767382","pmcid":null,"openalex_id":"https://openalex.org/W3198036342","authors":[],"funders":[],"total_grants":0,"fwci":0.0,"citation_percentile":0.14784108,"influential_citations":0,"citation_trend":[],"oa_status":"bronze","license":"https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model","oa_locations":[{"url":"https://academic.oup.com/ije/article-pdf/50/Supplement_1/dyab168.176/40212209/dyab168.176.pdf","host_type":"journal"},{"url":"https://academic.oup.com/ije/article-pdf/50/Supplement_1/dyab168.176/40212209/dyab168.176.pdf","host_type":"publisher"},{"url":"http://academic.oup.com/ije/article-pdf/50/Supplement_1/dyab168.176/40212209/dyab168.176.pdf","host_type":"publisher"},{"url":"https://doi.org/10.1093/ije/dyab168.176","host_type":"journal"}],"fields_of_study":["Gestational Diabetes Research and Management","Cardiovascular Issues in Pregnancy","Pregnancy and preeclampsia studies"],"mesh_terms":[],"keywords":["Pregnancy","Medicine","Obstetrics","Confounding","Placental abruption","Gestational age","Relative risk","Eclampsia","Premature birth","Gestation","Cohort study","Low birth weight","Birth weight","Confidence interval","Internal medicine"],"sdg_mappings":[{"sdg_number":0,"sdg_label":"Good health and well-being"}],"linked_datasets":[],"clinical_trials":[],"software_tools":[],"database_accessions":[],"source":"live","citation_network_status":"fetched"},"created_at":"2026-08-05T12:26:17.827524Z","pmid":null,"pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}