UOG Journal Club: August 2011

1. UOG Journal Club: August 2011 Systemic 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)

2. Multiple pregnancy 34 32 30 1–2% of all conceptions 28 (per 1000 total births) 26 24 22 20 1996 1998 2000 2002 2004 2006 2008 2010 1994 USA twin birth rate 1995–2008 National Vital Statistics Reports 2010

3. Multiple pregnancy Twin pregnancies are at increased risk of: Growth restriction Discordant anomaly Aneuploidy Accurate labeling is essential especially if invasive prenatal diagnosis or therapy is required Sebire NJ et al., BJOG 1997 Barigye O et al., PLoS Med 2005 Bhide A et al., UOG 2010 Centre for Maternal and Child Enquiries (CMACE) Perinatal Mortality 2008:UK

4. Current twin labeling methods based on proximity to cervix Presenting twin Twin 1 on left Presenting sac Twin 1 on right Evidence: none

5. Systemic labeling of twin pregnancies on ultrasound Dias et al., UOG 2011 Retrospective; 416 twin pregnancies at 11–14 weeks; 2000–2010 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

6. Methodology • 11–14 weeks • The cervical canal was identified • Relative orientation of the twins • Lateral • Vertical Subsequent scans: Which twin (left or right, top or bottom) was the presenting twin? Birth order: Sex and presenting order on the final scan prior to delivery was compared to the sex and birth order at delivery (N.B. neonatal convention dictates that first born is always Twin 1) Lateral (left/right) Vertical (top/bottom)

7. Results Subsequent scans: 11–14 weeks Changed by last scan Lateral (right/left) 378 (91%) 9% Vertical (top/bottom) 38 (9%) 0% Birth order: Number Change in twin order Vaginal delivery 34 5.9% Cesarean delivery 74 20% Total 108 15.7%

8. Lateral and vertical orientation unchanged throughout pregnancy 10% Presenting twin determined by proximity to cervix changes in 10% of left/right orientated pregnancy

9. Peripartum (birth order) switch 6% A peripartum switch in vaginal birth order may occur if Twin 2 delivers through a fold of the intertwin membrane.

10. Twins labeling – options and limitations • Fetal sex • Fetal sexing unreliable in early pregnancy • Precluded in same-sex twin pregnancy • Placental position • Changes with advancing gestation • Not in monochorionic or fused dichorionic twin pregnancy • Gestational sac position • and orientation • The position of the gestational sac in relation to the cervix remains constant • The base of the intertwin membrane is immobile • Fetal position • The position of either fetus relative to the cervix changes in pregnancy • Fetuses are free to move independently of each other

11. Systemic labeling of twin pregnancies on ultrasound Dias et al., UOG 2011 • Conclusion • Antenatal labeling of twins according to laterality or vertical orientation is reliable • The use of orientation for antenatal labeling of twins rather than assignment of a number based on proximity to the cervix precludes misconceptions regarding which twin will be born first