UOG Journal Club: August 2011Systemic labeling of twin pregnancies on ultrasound

T Dias, S Ladd, S Mahsud-Dornan, A Bhide, A T Papageorghiou and B Thilaganathan Volume 38, Issue 2, Date: August 2011, pages 130–133

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

1–2% of all conceptions

Multiple pregnancyMultiple pregnancy

National Vital Statistics Reports 2010

20

22

24

26

28

30

32

34

1994 1996 1998 2000 2002 2004 2006 2008 2010

(pe

r 1

00

0 to

tal b

irth

s)

USA twin birth rate 1995–2008

Discordantanomaly

Aneuploidy Growthrestriction

Twin pregnancies are at increased Twin pregnancies are at increased risk of:risk of:

Accurate labeling is essential especially if invasive prenatal Accurate labeling is essential especially if invasive prenatal diagnosis or therapy is requireddiagnosis or therapy is required

Multiple pregnancyMultiple pregnancy

Sebire NJ et al., BJOG 1997Barigye O et al., PLoS Med 2005

Bhide A et al., UOG 2010Centre for Maternal and Child Enquiries (CMACE) Perinatal Mortality 2008:UK

Presenting sacPresenting sac

Twin 1 on rightTwin 1 on right

Current twin labeling methods Current twin labeling methods based on proximity to cervixbased on proximity to cervix

Presenting twinPresenting twin

Twin 1 on leftTwin 1 on left

Evidence: none

Systemic labeling of twin pregnancies on ultrasoundDias et al., UOG 2011

Objectives

1. Describe a standard method of twin labeling in the first trimester of pregnancy

2. Assess the reliability of this technique in predicting the presenting twin in subsequent scans

3. Assess the reliability of this technique in predicting the birth order at delivery

Retrospective; 416 twin pregnancies at 11–14 weeks; 2000–2010Retrospective; 416 twin pregnancies at 11–14 weeks; 2000–2010

Lateral(left/right)

Vertical(top/bottom)

MethodologyMethodology

11–14 weeks11–14 weeks

•The cervical canal was identified•Relative orientation of the twins

Lateral Vertical

Subsequent scans: Subsequent scans:

Which twin (left or right, top or Which twin (left or right, top or bottom) was the presenting twin?bottom) was the presenting twin?

Birth order:Birth order:

Sex and presenting order on the final Sex and presenting order on the final scan prior to delivery was compared scan prior to delivery was compared to the sex and birth order at deliveryto the sex and birth order at delivery(N.B. neonatal convention dictates (N.B. neonatal convention dictates that first born is always Twin 1)that first born is always Twin 1)

ResultsResults

Vertical (top/bottom)Vertical (top/bottom) 38 (9%) 0%

9%Lateral (right/left)Lateral (right/left) 378 (91%)

Birth order:Birth order:

Subsequent scans:Subsequent scans:

Changed by last scanChanged by last scan1111––14 weeks14 weeks

Cesarean delivery Cesarean delivery 74 20%

5.9%Vaginal deliveryVaginal delivery 34

Change in twin orderChange in twin orderNumberNumber

TotalTotal 108 15.7%

Presenting twin determined by proximity to cervix changes Presenting twin determined by proximity to cervix changes in 10% of left/right orientated pregnancyin 10% of left/right orientated pregnancy

Lateral and vertical orientation Lateral and vertical orientation unchanged throughout pregnancyunchanged throughout pregnancy

10%10%

Peripartum (birth order) switchPeripartum (birth order) switch

A peripartum switch in vaginal birth order may occur ifA peripartum switch in vaginal birth order may occur ifTwin 2 delivers through a fold of the intertwin membrane.Twin 2 delivers through a fold of the intertwin membrane.

6%6%

Placental positionPlacental position

1)1) Changes with advancing Changes with advancing gestationgestation

2)2) Not in monochorionic or fused Not in monochorionic or fused dichorionic twin pregnancydichorionic twin pregnancy

Fetal sexFetal sex

1)1) Fetal sexing unreliable in early Fetal sexing unreliable in early pregnancypregnancy

2)2) Precluded in same-sex twin Precluded in same-sex twin pregnancypregnancy

Gestational sac positionGestational sac positionand orientationand orientation

1)1) The position of the gestational The position of the gestational sac in relation to the cervix sac in relation to the cervix remains constantremains constant

2)2) The base of the intertwin The base of the intertwin membrane is immobilemembrane is immobile

Fetal positionFetal position

1)1) The position of either fetus The position of either fetus relative to the cervix changes relative to the cervix changes in pregnancyin pregnancy

2)2) Fetuses are free to move Fetuses are free to move independently of each otherindependently of each other

Twins labeling – options and limitationsTwins labeling – options and limitations

Systemic labeling of twin pregnancies on ultrasoundDias et al., UOG 2011

ConclusionConclusion Antenatal labeling of twins according to laterality orAntenatal labeling of twins according to laterality or vertical orientation is reliable vertical orientation is reliable

The use of orientation for antenatal labeling ofThe use of orientation for antenatal labeling of twins rather than assignment of a number twins rather than assignment of a number based on proximity to the cervix precludes based on proximity to the cervix precludes misconceptions regarding which twin will be born first misconceptions regarding which twin will be born first