uog journal club: may 2012

UOG Journal Club: May 2012Prospective risk of late stillbirth in monochorionic twins:

a regional cohort studySouthwest Thames Obstetric Research Collaborative (STORK)

Volume 39, Issue 5, Date: May 2012, pages 500–504

Journal Club slides prepared by Dr Asma Khalil(UOG Editor for Trainees)

Stillbirth rate in twin pregnancyCurrent evidence

Joseph K et al., BMC Pregnancy Childbirth 2003

0

1

2

3

4

5

6

7

8

9

10

28 30 32 34 36 38 40 42

Gestational age (weeks)

Sti

llb

irth

rat

e p

er 1

000

fetu

ses

at r

isk

TwinsSingleton

Large numbers (n = 35 647)But no data on chorionicity

Sebire NJ et al., BJOG 1997

Cu

mu

lati

ve l

oss

rat

e (%

)

Gestation (weeks)

Monochorionic

Dichorionic

Cumulative perinatal loss rate in twinsCurrent evidence

Fetuses (%) 12.2 1.8*

2.5*Pregnancies (%) 12.7

Fetal loss: DCMC

Fetuses (%) 2.8 1.6

2.8Pregnancies (%) 4.9

Perinatal loss:

* P < 0.05

Chorionicity dataBut small numbers (n = 467)

Prospective risk of late stillbirth in monochorionic twins: a regional cohort study

STORK, UOG 2012

Objective

Evaluate the prospective risk of late stillbirth in a large regionalcohort of twin pregnancies of known chorionicity

Retrospective data;3005 twin pregnanciesdelivered after 26 weeksfrom 2000 to 2009

Methodology

Inclusion criteria

1) Confirmed diamniotic twin pregnancy at 11 weeks

2) 9 hospitals in the Southwest Thames region of England

3) 2000-2009

Exclusion criteria

1) Unknown chorionicity 2) Delivery < 26 weeks3) TOP 4) Stillbirth with a birth weight of < 500g

Data sources

•Scan data: computerized search of each hospital’s obstetric ultrasound computer database of all twins at 11–14-week nuchal scan•Stillbirth data: Centre for Maternal and Child Enquiries (CMACE)

Mandatory national register of all stillbirths GA at IUD and delivery

•Computerized maternity records were cross-linked to stillbirth data

SOUTHWEST THAMES OBSTETRIC RESEARCH COLLABORATIVE (STORK)SOUTHWEST THAMES OBSTETRIC RESEARCH COLLABORATIVE (STORK)

Nine UK hospitals, 16 collaboratorsNine UK hospitals, 16 collaborators

Pregnancy management

11–14 weeks

•GA according to the CRL

•Chorionicity (lambda/T-signs)

20–22 weeks

•Routine anomaly scan

3rd trimester

•Ultrasound every 3–5 weeks

•Scans more frequently as clinically indicated

•MC twins had additional scans at 17 and 19 weeks (for TTTS)

Delivery

• Mode according to patient’s decision and local clinical practice • Routine IOL ≥ 38 weeks

• Elective CS ≥ 36 weeks for MC and ≥ 37 weeks for DC twins

Analysis

• SB risk: derived for each 2-week GA interval from 26 weeks

• SB risk expressed per fetus

Results

Birth weight centile 18.4 (4.0–44.8) 22.9 (6.2–50.7)*

37 (35–38)*GA at delivery (weeks) 36 (34–37)

Stillbirths

Live births DC pregnancies (n = 2424)

MC pregnancies (n = 528)

DC pregnancies (n = 32)

MC pregnancies (n = 21)

Birth weight centile 3.9 (0.2–28.3) 1.1 (0.1–10.0)

34 (32–36)GA at death (weeks) 32 (31–34)

* P < 0.05

Gestational age (weeks)

Bir

th (

%)

Monochorionic

Dichorionic

Timing of birth in twin pregnancy

Modal time of deliveryMC = 36–37 weeksDC = 37–38 weeks

Late stillbirth risk in twin pregnancy

SB risk in MC twins did not change significantly between 26 and 36 weeks (OR = 1.85 (0.3–13.2))

0

1

2

3

4

5

6

7

8

9

26 28 30 32 34 ≥ 36

Sti

llbir

th r

isk

per

10

00 o

ng

oin

g f

etu

ses

Gestational age (weeks)

Monochorionic

Dichorionic

Late stillbirth risk in twin pregnancy Risk of stillbirth compared to 26+0–27+6 weeks

Total stillbirth rate: MC twins = 19.1 (12.5–29.1) fetuses/1000 ongoing fetuses DC twins = 6.5 (4.6–9.2) ) fetuses/1000 ongoing fetuses OR = 2.97 (95% CI 1.7–5.28)

0.1 1 10

28-30

30-32

32-34

34-36

>36

Odds ratio

Monochorionic

Ges

tati

on

al a

ge

(wee

ks)

0.1 1 10

28-30

30-32

32-34

34-36

>36

Odds ratioG

esta

tio

nal

ag

e (w

eeks

)

Dichorionic

Strengths

Current study

•Management according to a protocol consistent with current clinical practice•Modal time of delivery for MC and DC twins of 36 and 37 wk•Largest twin cohort to provide data on chorionicity-related risk of late SB

Previous studies

• Smaller numbers

• No standardized protocol for fetal surveillance

• Elective delivery of many MC twins before 37 weeks

• Retrospective design (validation of the ultrasound database against delivery suite and national SB registers)• Assumptions made about GA at which IUD was diagnosed

Limitations

Stillbirth risk

Total stillbirth rate >26 weeks approaches 2% in MC twins

Late preterm delivery

1) Infant death rate >32 weeks is 1%

2) Respiratory distress syndrome at 32 weeks 5%

3) Cerebral palsy is 3 x higher at 34 weeks than at term

Stillbirth versus prematurity

Conclusion The risk of SB in MC twins does not appear to increase significantly near term

The data do not support a policy of elective delivery at less than 36 weeks in uncomplicated MC twins

Prospective risk of late stillbirth in MC twins STORK, UOG 2012

Prospective risk of late stillbirth in MC twins STORK, UOG 2012

• What is your local hospital policy for timing of delivery of MC and DC twins?

• Is the clinical evidence for your local policy robust?

• How did the researchers capture all twin pregnancies in this cohort?

• How did the researchers capture all the stillbirths from this cohort?

• Was the stillbirth risk in MC different from that of DC twins?

• Did the stillbirth risk in MC twins increase significantly at any gestational age?

• Do the risks of continuing MC pregnancy beyond 34 weeks’ gestation outweigh the risks of preterm delivery?

Discussion points