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Temporal trends in stillbirth in the U nited S tates, 1992–2004: a population‐based cohort study
Author(s) -
Zhang X,
Kramer MS
Publication year - 2014
Publication title -
bjog: an international journal of obstetrics and gynaecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.157
H-Index - 164
eISSN - 1471-0528
pISSN - 1470-0328
DOI - 10.1111/1471-0528.12883
Subject(s) - medicine , hazard ratio , demography , obstetrics , population , singleton , proportional hazards model , cohort , gestational age , pregnancy , confidence interval , biology , environmental health , genetics , sociology
Objective To examine temporal trends in stillbirth and its risk factors in the U nited S tates ( US ), and to assess the contribution of labour induction and caesarean delivery to the stillbirth rate. Design Population‐based cohort study based on linked birth‐infant death and fetal death data files from the US N ational V ital S tatistics S ystem. Setting Complete data were available for 44 states and the D istrict of C olumbia. Population or Sample Singleton births from 1992 to 2004. Methods We assessed changes in stillbirth rates from 1992–1994 to 2002–2004 before and after adjustment for changes in maternal characteristics including maternal age, education, smoking, and medical risk factors, using C ox regression models. We also carried out an ecological study, using states as the units of analysis, to assess the impact on the stillbirth rate of increasing induction and caesarean delivery. Race‐specific subgroup analyses were performed and included non‐ H ispanic W hites and non‐ H ispanic B lacks. Main outcome measure Stillbirth rate. Results The stillbirth rate among non‐ H ispanic W hite singleton births decreased 11.5% from 1992–1994 (5.2 per 1000) to 2002–2004 (4.6 per 1000). After adjustment for maternal risk factors, the hazard ratio ( HR ) for 2002–2004 was 1.01 (0.99, 1.03) for gestational age ( GA ) ≤39 weeks, but 0.92 (0.86, 0.99) at 40 or more weeks. The ecologic analysis revealed a nonsignificant negative correlation of −0.17 (−0.44, 0.13) between state‐level changes in stillbirth at GA ≥40 weeks and labour induction. A nonsignificant positive correlation of 0.23 (−0.07, 0.49) was observed between changes in stillbirth at all GA s and caesarean delivery and did not differ at GA ≤39 versus ≥40 weeks. Results were similar among non‐ H ispanic B lacks. Conclusions Changes in maternal risk factors explained the reduction in stillbirth at GA ≤39 weeks but not at ≥40 weeks. The rise in labour induction and caesarean delivery rates did not explain the reduction in stillbirth ≥40 weeks of gestation.