{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,16]],"date-time":"2026-10-16T02:55:12Z","timestamp":1792119312988,"version":"4.4.0"},"reference-count":54,"publisher":"Wiley","issue":"4","license":[{"start":{"date-parts":[[2020,12,3]],"date-time":"2020-12-03T00:00:00Z","timestamp":1606953600000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":["onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Paediatric Perinatal Epid"],"published-print":{"date-parts":[[2021,7]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:sec><jats:title>Background<\/jats:title><jats:p>Estimation of causal effects of short interpregnancy interval on pregnancy outcomes may be confounded by time\u2010varying factors. These confounders should be ascertained at or before delivery of the first (\u201cindex\u201d) pregnancy, but are often only measured at the subsequent pregnancy.<\/jats:p><\/jats:sec><jats:sec><jats:title>Objectives<\/jats:title><jats:p>To quantify bias induced by adjusting for time\u2010varying confounders ascertained at the subsequent (rather than the index) pregnancy in estimated effects of short interpregnancy interval on pregnancy outcomes.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods<\/jats:title><jats:p>We analysed linked records for births in British Columbia, Canada, 2004\u20102014, to women with \u22652 singleton pregnancies (n\u00a0=\u00a0121\u00a0151). We used log binomial regression to compare short (&lt;6, 6\u201011, 12\u201017\u00a0months) to 18\u201023\u2010month reference intervals for 5 outcomes: perinatal mortality (stillbirth and neonatal death); small for gestational age (SGA) birth and preterm delivery (all, early, spontaneous). We calculated per cent differences between adjusted risk ratios (aRR) from two models with maternal age, low socio\u2010economic status, body mass index, and smoking ascertained in the index pregnancy and the subsequent pregnancy. We considered relative per cent differences &lt;5% minimal, 5%\u20109% modest, and \u226510% substantial.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>Adjustment for confounders measured at the subsequent pregnancy introduced modest bias towards the null for perinatal mortality aRRs for &lt;6\u2010month interpregnancy intervals [\u22129.7%, 95% confidence interval [CI] \u221215.3, \u22126.2). SGA aRRs were minimally biased towards the null (\u22121.1%, 95% CI \u22122.6, 0.8) for &lt;6\u2010month intervals. While early preterm delivery aRRs were substantially biased towards the null (\u221210.4%, 95% CI \u221214.0, \u22126.6) for &lt;6\u2010month interpregnancy intervals, bias was minimal for &lt;6\u2010month intervals for all preterm deliveries (\u22120.6%, 95% CI \u22122.0, 0.8) and spontaneous preterm deliveries (\u22121.3%, 95% CI \u22123.1, 0.1). For all outcomes, bias was attenuated and minimal for 6\u201011\u2010month and 12\u201017\u2010month interpregnancy intervals.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusion<\/jats:title><jats:p>These findings suggest that maternally linked pregnancy data may not be needed for appropriate confounder adjustment when studying the effects of short interpregnancy interval on pregnancy outcomes.<\/jats:p><\/jats:sec>","DOI":"10.1111\/ppe.12716","type":"journal-article","created":{"date-parts":[[2020,12,3]],"date-time":"2020-12-03T17:32:58Z","timestamp":1607016778000},"page":"428-437","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":10,"title":["Short interpregnancy interval and pregnancy outcomes: How important is the timing of confounding variable ascertainment?"],"prefix":"10.1111","volume":"35","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-3536-0498","authenticated-orcid":false,"given":"Laura","family":"Schummers","sequence":"first","affiliation":[{"name":"Department of Family Practice University of British Columbia Vancouver BC Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6618-6018","authenticated-orcid":false,"given":"Jennifer A.","family":"Hutcheon","sequence":"additional","affiliation":[{"name":"Department of Obstetrics and Gynaecology University of British Columbia Vancouver BC Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4340-7882","authenticated-orcid":false,"given":"Wendy V.","family":"Norman","sequence":"additional","affiliation":[{"name":"Department of Family Practice University of British Columbia Vancouver BC Canada"},{"name":"Faculty of Public Health &amp; Policy London School of Hygiene &amp; Tropical Medicine London UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1573-5574","authenticated-orcid":false,"given":"Jessica","family":"Liauw","sequence":"additional","affiliation":[{"name":"Department of Obstetrics and Gynaecology University of British Columbia Vancouver BC Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4000-8715","authenticated-orcid":false,"given":"Talshyn","family":"Bolatova","sequence":"additional","affiliation":[{"name":"Department of Family Practice University of British Columbia Vancouver BC Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5139-9208","authenticated-orcid":false,"given":"Katherine A.","family":"Ahrens","sequence":"additional","affiliation":[{"name":"Muskie School of Public Policy University of Southern Maine Portland ME USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2020,12,3]]},"reference":[{"key":"e_1_2_8_2_1","doi-asserted-by":"publisher","DOI":"10.1111\/ppe.12503"},{"key":"e_1_2_8_3_1","doi-asserted-by":"publisher","DOI":"10.1001\/jama.295.15.1809"},{"key":"e_1_2_8_4_1","doi-asserted-by":"publisher","DOI":"10.1097\/AOG.0000000000001913"},{"key":"e_1_2_8_5_1","doi-asserted-by":"publisher","DOI":"10.1111\/ppe.12504"},{"key":"e_1_2_8_6_1","doi-asserted-by":"publisher","DOI":"10.1111\/ppe.12512"},{"key":"e_1_2_8_7_1","doi-asserted-by":"publisher","DOI":"10.1363\/47e2615"},{"key":"e_1_2_8_8_1","doi-asserted-by":"publisher","DOI":"10.1097\/AOG.0b013e3182955e58"},{"key":"e_1_2_8_9_1","doi-asserted-by":"publisher","DOI":"10.1097\/EDE.0000000000000818"},{"key":"e_1_2_8_10_1","doi-asserted-by":"publisher","DOI":"10.1371\/journal.pone.0186287"},{"key":"e_1_2_8_11_1","doi-asserted-by":"publisher","DOI":"10.1016\/S1701-2163(15)30865-3"},{"key":"e_1_2_8_12_1","doi-asserted-by":"publisher","DOI":"10.1097\/AOG.0000000000000591"},{"key":"e_1_2_8_13_1","doi-asserted-by":"publisher","DOI":"10.1097\/AOG.0000000000000565"},{"issue":"6","key":"e_1_2_8_14_1","doi-asserted-by":"crossref","first-page":"532","DOI":"10.1034\/j.1600-0412.2001.080006532.x","article-title":"Choice and chance: determinants of short interpregnancy intervals in Denmark","volume":"80","author":"Kaharuza FM","year":"2001","journal-title":"Acta Obstet Gynecol Scand"},{"key":"e_1_2_8_15_1","doi-asserted-by":"publisher","DOI":"10.1177\/1933719114556486"},{"issue":"239","key":"e_1_2_8_16_1","first-page":"1","article-title":"Maternal smoking and the risk of still birth: systematic review and meta\u2010analysis","volume":"15","author":"Marufu TC","year":"2015","journal-title":"BMC Public Health"},{"key":"e_1_2_8_17_1","doi-asserted-by":"publisher","DOI":"10.1046\/j.1365-3016.2000.00266.x"},{"key":"e_1_2_8_18_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.whi.2017.02.011"},{"key":"e_1_2_8_19_1","doi-asserted-by":"publisher","DOI":"10.1007\/s10995-012-0948-4"},{"key":"e_1_2_8_20_1","doi-asserted-by":"publisher","DOI":"10.1089\/jwh.2010.2397"},{"key":"e_1_2_8_21_1","doi-asserted-by":"publisher","DOI":"10.1111\/ppe.12560"},{"key":"e_1_2_8_22_1","doi-asserted-by":"publisher","DOI":"10.1097\/EDE.0b013e3181a819a1"},{"key":"e_1_2_8_23_1","doi-asserted-by":"publisher","DOI":"10.1093\/ije\/dyp334"},{"key":"e_1_2_8_24_1","first-page":"183","volume-title":"Modern Epidemiology","author":"Glymour M","year":"2008"},{"key":"e_1_2_8_25_1","doi-asserted-by":"publisher","DOI":"10.1111\/ppe.12587"},{"key":"e_1_2_8_26_1","doi-asserted-by":"publisher","DOI":"10.1186\/s12884-015-0563-7"},{"key":"e_1_2_8_27_1","volume-title":"British Columbia Perinatal Data Registry","author":"Perinatal Services BC [creator]","year":"2016"},{"key":"e_1_2_8_28_1","unstructured":"Population Data BC. 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