1. Stillbirth in twins, exploring the optimal gestational age for delivery: a retrospective cohort study S Wood, S Tang, S Ross, R Sauve

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3. Scenario A 36-year-old nulliparous Caucasian woman with dichorionic diamniotic twins at 32 weeks attends your antenatal clinic to discuss her birth plan. The twins were conceived by in vitro fertilization. No cause has been found for this woman’s subfertility, and she has no other medical history. The latest fetal ultrasound scan shows fetal growth and amniotic fluid volume are within normal ranges. Fetal umbilical artery doppler results are normal for both twins. Both are in cephalic presentation. How would you counsel her?

4. The Clinical Question What is the optimal gestational age at birth for dichorionic and monochorionic diamniotic twins?

5. Description of Research ParticipantsAll twin births (N= 17724) in Alberta, Canada from 1992- 2007 in which the fetuses survived until >23 weeks InterventionDelivery of twins at different gestational ages ComparisonExpectant management OutcomesStillbirths (fetal deaths at >23 weeks), neonatal deaths and Perinatal Risk Ratio

6. Background Previous cohort studies suggested increase risk of stillbirth in twins between 37 and 39 weeks of gestation Gestational age at stillbirth can be difficult to determine in twins if only one twin is affected Optimal gestational age of delivery for twins have not been conclusively determined

7. Background What are your current recommendations on the timing of delivery for twins? What are the reasons behind them?

9. Methods Data on maternal demographics, pregnancy complications, delivery data and outcomes were retrieved from the Alberta Perinatal Health Project Gestational ages at stillbirth were determined by searching through stillbirth records – Stillbirth: >20weeks in utero or birth weight >500g Independently reviewed by two co-investigators. Analysis with fetus at risk approach and Perinatal Risk Ratio were performed.

10. Methods Critically appraise this studying using the Scottish Intercollegiate Guidelines Network (SIGN) Checklist for cohort studies (See checklist 3; http://bit.ly/1rzfjfD). http://bit.ly/1rzfjfD What are the advantages and disadvantages of using a historical cohort study to answer the current research question?

11. Results Data of 17724 twin births were retrieved – Excluded 93 Perinatal Deaths due to anomaly. Stillbirths and neonatal deaths (see flow chart) – 202 antepartum stillbirths. – 18 intrapartum stillbirths. – 193 neonatal deaths. 91/220 (39%) stillbirths occurred >1 week prior to delivery

13. Perinatal Risk Ratio A proposed rate ratio of risk of death from delivery versus risk of stillbirth in next week Formulae used When RR>1 favors expectant management. When RR<1 favors delivery.

15. GA in Weeks

16. Authors’ Interpretation The estimated risk of stillbirth is greater than the risk of neonatal death for diamniotic monochorionic twins in the 37 th week. The estimated risk of stillbirth is greater than the risk of neonatal death for diamniotic dichorionic twins in the 38 th week. In both cases the risk of stillbirth is low.

17. Results How do your local stillbirth and neonatal death rates compared to the data reported in this study? Can you summarise the available evidence in a single sentence? How would the results of this study influence your practice?

18. Can we individualize care using fetal biometry? ≥ 37 weeks 24 Antepartum Stillbirths – 9 Dichorionic – 14 Diamniotic Monochorionic – 1 unknown chorionicity Dichorionic Twins with Antepartum Stillbirth – 5/9 SGA and 2/9 >20% BW discrepancy Diamniotic Monochorionic – 4/14 SGA and 3/14 >20% BW discrepancy

19. Authors’ Interpretation Almost half of diamniotic dichorionic twins with stillbirth ≥37 weeks had neither SGA or a significant size discrepancy with their co-twin. This was the case in the majority of stillbirths in diamniotic monochorionic twins. Fetal growth parameters may not allow individualization of timing of delivery at term.

20. Authors’ Conclusions Our data would support delivery of diamniotic monochorionic twins at 36 weeks prior to the increase in risk in the 37 th week. Delivery of diamniotic dichorionic twins can be justified at the end of the 37 th week or beginning of 38 th week. This study did not analyse neonatal morbidity from early term delivery.

21. Suggested reading Dodd JM, Deussen AR, Grivell RM, Crowther CA. Elective birth at 37 weeks' gestation for women with an uncomplicated twin pregnancy. Cochrane Database Syst Rev. 2014 Feb 10;2:CD003582.

22. Authors Dr. Stephen WOOD MD MSc Department of Obstetrics & Gynecology and Community Health Sciences, University of Calgary, Calgary, Alberta, Canada. Ms. Selphee TANG BSc Department of Obstetrics & Gynecology and Community Health Sciences, University of Calgary, Calgary, Alberta, Canada. Dr. Sue ROSS PhD Department of Obstetrics & Gynecology and Community Health Sciences, University of Calgary, Calgary, Alberta, Canada. Dr Reg SAUVE MD MPH Department of Pediatrics and Community Health Sciences, University of Calgary, Calgary Alberta, Canada. Corresponding author: Dr. Stephen Wood, Department of Obstetrics and Gynecology. stephen.wood@albertahealthservices.ca stephen.wood@albertahealthservices.ca