Monoamniotic Twinning: Evaluation and Management

Contributor: MFM Division
Last Update: 1/27/2015

Background
Monoamniotic twins are the least common type of twins, occurring just 1:10,000 pregnancies and complicating only 1%-5% of monozygotic twin gestations.  It is the result of a single embryo dividing between 8-12 days post-fertilization.  The perinatal mortality rate is very high, ranging between 10% – 40% (Murata, Van Mieghem) .  Because the frequency is so low, the management of monoamniotic twins is controversial due to the lack of a strong evidence base for antepartum management.

Diagnosis:
The optimal time for diagnosing chorionicity is in the first trimester, and ideally at 9-10 weeks gestational age.  If monoamniotic twins are suspected, recommend referral to maternal fetal medicine as early in pregnancy as possible.

Ultrasound criteria:

• Same sex twins
• No evidence of dividing membrane, seen on at least two consecutive ultrasound examinations
• Single placenta
• Normal amniotic fluid volume with 2 free-floating fetuses
• Unrestricted fetal movement (no evidence of stuck twin or conjoined twins)
• Cord entanglement, as seen by color Doppler and/or 3D ultrasound
• <span “font-size:10.0pt;mso-bidi-font-size:11.0pt;font-family:symbol;=”” mso-fareast-font-family:symbol;mso-bidi-font-family:symbol”=””> One yolk sac (first trimester)
• Visualization of 2 cord insertions into the placenta in close proximity is suggestive of monoamnionicity.

Management:
Genetic counseling at diagnosis; screening for fetal aneuploidy
Ultrasound evaluation:

• Ultrasound assessment every two weeks between 14-23 weeks gestational age due to the high risk for fetal demise and twin to     twin transfusion.
• Evaluation of fetal growth every 3-4 weeks.
• Comprehensive anatomy at 18-22 weeks with fetal echocardiogram
• Weekly biophysical profile with umbilical artery Doppler interrogation beginning at 23-26 weeks gestational age

Recommend routine (prophylactic) antenatal corticosteroids at 26-28 weeks gestational age, or earlier if signs of fetal compromise are present.  A second full course can be repeated prior to delivery at 32-34 weeks gestational age or sooner if 4 weeks have elapsed since the first course and delivery is imminent.

Management options at viability:
There is no consensus regarding optimal management of monoamniotic twin pregnancies.  These pregnancies warrant a high level of surveillance due to the high rates of fetal loss, which is often due to cord entanglement.  Patients should be informed of the risks and benefits of inpatient vs. outpatient management and should be active participants in developing the surveillance plan.

• Intensive inpatient management to begin at 26-28 weeks gestational age

1.     Three times daily monitoring for two hours each time (total 6 hours CEFM daily)
2.     Weekly biophysical profile with umbilical artery Doppler studies
3.     Growth scan every 3 weeks

• Intensive outpatient management to begin at 26-28 weeks gestational age

1.     May only be offered to patients with reliable transportation, who live within a relatively close proximity to the                                         office and who have the ability to attend visits regularly
2.     Prolonged non-stress testing for one hour 4-7 times weekly
3.     Twice weekly biophysical profile
4.     Admission if any testing is non-reassuring, or if patient desires

Delivery:
For single intrauterine death <23 weeks, outpatient observation.  For single intrauterine death >24 weeks, admit for evaluation and CEFM.  There should be a low threshold for delivery of surviving twin

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References

1. Baxi LV1, Walsh CA. Monoamniotic twins in contemporary practice: a single-center study of perinatal outcomes. J Matern Fetal Neonatal Med. 2010 Jun;23(6):506-10
2. Desai N, Lewis D, Sunday S, Rochelson B. Current antenatal management of monoamniotic twins: a survey of maternal-fetal medicine specialists.J Matern Fetal Neonatal Med. 2012 Oct;25(10):1913-6. Epub 2012 Mar 28.
3. Dias T1, Mahsud-Dornan S, Bhide A, Papageorghiou AT, Thilaganathan B. Cord entanglement and perinatal outcome in monoamniotic twin pregnancies.  Ultrasound Obstet Gynecol. 2010 Feb;35(2):201-4.
4. Hack KE, Derks JB, Schaap AH, Lopriore E, Elias SG, et al.  Perinatal outcome of monoamniotic twin pregnancies.  Obstet Gynecol. 2009;113(2 Pt 1):353.
5. Murata M, Ishii K, Mamitomo M, Murakoshi T, Takahashi Y, Sekino M, et al.  Perinatal outcome and clinical features of monochorionic monoamniotic twin gestation.  J Obstet Gynecol Res 2013;39:922.
6. Van Mieghem T, De Heus R, Lewi L, Klaritsch P, Kollman M, et al.  Prenatal management of monoamniotic twin pregnancies. Obstet Gynecol 2014;124(3):498-506.