mortality of twins and singletons
DESCRIPTION
Mortality of Twins and Singletons. Yin Bun Cheung, Ph.D. Paul Yip, Ph.D. Johan Karlberg, M.D., Ph.D. Readings. Objectives: mortality patterns. Understand the patterns of gestational age-specific neonatal mortality in twins and singletons. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/1.jpg)
Mortality of Twins and Singletons
Yin Bun Cheung, Ph.D.
Paul Yip, Ph.D.
Johan Karlberg, M.D., Ph.D.
Readings
![Page 2: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/2.jpg)
Objectives: mortality patterns
• Understand the patterns of gestational age-specific neonatal mortality in twins and singletons.
• Appreciate the (non-) comparability between twins and singletons.
![Page 3: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/3.jpg)
Objectives: statistical models
• Learn a flexible way to handle interaction / effect-modification.
• Interpretation of a (logistic) regression model in different ways.
![Page 4: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/4.jpg)
Mortality by gestational age
• Does the mortality difference between twins & singletons depend on gestational age?
• Do twins and singletons have the same gestational age pattern of mortality?
![Page 5: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/5.jpg)
Difficulties in research
• Sample size
• Referral bias
• Statistical adjustment / matching
![Page 6: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/6.jpg)
A study based on Swedish Medical Birth Registry
• All births born in Sweden in 1982-1995.
• Includes 32,942 twins and 1.5 million singletons.
• Details in Reading 1.
![Page 7: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/7.jpg)
Cumulative distribution of GA
0
25
50
75
100
24 26 28 30 32 34 36 38 40 42
Gestational age (weeks)
Per
cen
t
.
Singletons
Twins
![Page 8: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/8.jpg)
Odds ratios of short GA in twins and singletons
Risk factors Twins Singletons
Mother smoke 1.16* 1.39*
Prior still-birth 0.87 1.57*
Goodness-of-fit P=0.08 P=0.14
* P<0.05
![Page 9: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/9.jpg)
Varying-coefficient model
Mortality impact of twin pregnancy as a function of GA:
Log odds=a1+b1GA+b2GA2+ (a2+c1GA+c2GA2)Twin+...
![Page 10: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/10.jpg)
Varying-coefficient model
As a model of separate curves:
Log odds in singletons:
a1+b1GA+b2GA2
Log odds in twins:
(a1+a2)+(b1+c1)GA+(b2+c2)GA2
![Page 11: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/11.jpg)
Birth weight SDS by GA
-3-2-10123
28 30 32 34 36 38 40 42
Gestational age (weeks)
Mea
n SD
S
SingletonsTwins
![Page 12: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/12.jpg)
Size at birth in twins
Growth restriction in twins concentrates in late pregnancy.
•Physical constraints in utero?
•Limited placental function?
•Selection bias?
![Page 13: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/13.jpg)
Neonatal deaths per 1000
020406080
100120140160180200
28 30 32 34 36 38 40 42
Gestational age (weeks)
Neo
nat
al d
eath
SingletonsTwins
![Page 14: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/14.jpg)
A varying-coefficient logistic regression model
• The impact of twin pregnancy as a quadratic function of GA.
• Adjusted for confounders, e.g. prior still-birth, smoking.
• With & without adjustment for size at birth.
![Page 15: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/15.jpg)
Log OR, fully adjusted
-2
-1
0
1
2
3
4
5
28 30 32 34 36 38 40 42
Gestational age (weeks)
Log
odd
s ra
tio
![Page 16: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/16.jpg)
Log odds, fully adjusted
-6
-4
-2
0
2
4
28 30 32 34 36 38 40 42
Gestational age (weeks)
Log
odd
s
Singletons
Twins
![Page 17: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/17.jpg)
Is twin birth hazardous? Why?
• Twins had lower odds of death prior to 36 weeks of GA; higher odds thereafter.
• Longer GA was related to lower mortality. But the decline was sharper in singletons than in twins.
![Page 18: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/18.jpg)
Log OR, not adjusted for size at birth
-2
-1
0
1
2
3
4
5
28 30 32 34 36 38 40 42
Gestational age (weeks)
Log
odd
s ra
tio
![Page 19: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/19.jpg)
Log odds, not adjusted for size at birth
-6
-4
-2
0
2
4
28 30 32 34 36 38 40 42
Gestational age (weeks)
Log
odd
s
Singletons
Twins
![Page 20: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/20.jpg)
The role of fetal growth and size at birth?
• Without adjustment for size at birth the log OR climbed up faster after around 34 weeks.
• Twins’ mortality reached it’s lowest point at 38 weeks; it turned upward after that.
![Page 21: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/21.jpg)
Clinical interpretations
• Twins have an earlier development
• In utero environment in late pregnancy not good for twins
• Residual confounding
![Page 22: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/22.jpg)
Optimal GA for twins
The optimal gestational age for twins appeared to be 37-39 weeks in terms of neonatal mortality.
This is earlier than singletons’.
![Page 23: Mortality of Twins and Singletons](https://reader035.vdocuments.us/reader035/viewer/2022062217/56814838550346895db55667/html5/thumbnails/23.jpg)
Readings1 Cheung YB, Yip P, Karlberg J. Mortality of
twins and singletons by gestational age. Am J Epidemiol 2000;152:1107-16.
2 Lie RT. Intersecting perinatal mortality curves by gestational age -- are appearances deceiving? Am J Epidemiol 2000;152:1117-19.
3 Cheung YB, Yip P, Karlberg J. Respond to “Are appearances deceiving”. Am J Epidemiol 2000;152:1120.