An acardiac twin refers to a haemodynamically disadvantaged non viable twin which occurs in association with a twin reversed arterial perfusion sequence.
This twin is also referred to as a recipient twin.
Acardiac twinning is thought to affect 1 in 100 monozygotic twin pregnancies and 1 in 35,000 pregnancies overall 2-3. There is no recognised familial recurrence.
The acardiac twin undergoes secondary atrophy of the heart and dependent organs (brain) and often develops a characteristic set of anomalies including acardia and acephalus. This twin exerts abnormal strain on the opposite (pump) twin by stealing its circulation.
There are two schools of thought in the pathogenesis of the acardiac twin.
- some propose that the primary defect is one of cardiac embryogenesis (dysmorphogenesis)
- others consider the primary cause being an abnormal vascular communication between embryos in the placenta with arterial to arterial communication leading to reversed flow of blood to the haemodynamically disadvantaged or recipient twin, with resulting secondary atrophy of the heart and dependent organs 5.
An acardiac twin can present with four morphological types
acardius anephus :
- most common type
- there is absence of the head and upper torso and limbs in the acardiac twin with preservation of the lower limbs, genitalia and abdominal viscera.
acardius anceps :
- most developed type
- rudimentary cranial structures present with otherwise persistent trunk, limbs and organs
- however lacks even a rudimentary heart
acardius amorphus :
- least differentiated type
- comprises of an amorphous mass of bone, muscle, fat and connective tissue
- if rudimentary nerve tissue is present, it is then called acardius myelantencephalus
acardius acormus :
- rarest type
- the only developed structure is the fetal head
- all other structures are essentially absent
- the umbilical cord insertion is directly into the fetal head
- pathologically, rudiments of thoracic structures may be present
While features can vary with each sub types, general features include
- fetal biometric discordance
- marked edema (fetal anasarca) of the affected twin with cystic changes
- normal or accelerated growth of the lower extremities
- umbilical cord to the acardiac twin is often quite short and may be difficult to identify
Shows reversed flow through the umbilical arteries to the affected fetus
The other donor (pump) twin may develop cardiac failure (hydrops) with a reported mortality of 50 - 75%.
Treatment and prognosis
The acardiac twin is non viable and the majority of efforts in management are focused or maintaining viability of the other donor (pump) twin including close surveillance for development of hydrops. Interrupting blood flow to the acardiac twin may be performed by various methods which include hysterotomy and removal of the acardiac twin, ligation of the umbilical cord and / or laser ablation of vessels.
- 1. Sullivan AE, Varner MW, Ball RH et-al. The management of acardiac twins: a conservative approach. Am. J. Obstet. Gynecol. 2003;189 (5): 1310-3. Am. J. Obstet. Gynecol. (link) - Pubmed citation
- 2. Rodeck CH, Whittle MJ. Fetal medicine, basic science and clinical practice. Elsevier Health Sciences. (2008) ISBN:0443104085. Read it at Google Books - Find it at Amazon
- 3. Moore TR, Gale S, Benirschke K. Perinatal outcome of forty-nine pregnancies complicated by acardiac twinning. Am. J. Obstet. Gynecol. 1990;163 (3): 907-12. - Pubmed citation
- 4. Sepúlveda WH, Quiroz VH, Giuliano A et-al. Prenatal ultrasonographic diagnosis of acardiac twin. J Perinat Med. 1993;21 (3): 241-6. - Pubmed citation
- 5. Coulam CB, Wright G. First trimester diagnosis of acardiac twins. Early Pregnancy. 2000;4 (4): 261-70. - Pubmed citation
- 6. Arias F, Sunderji S, Gimpelson R et-al. Treatment of acardiac twinning. Obstet Gynecol. 1998;91 (5 Pt 2): 818-21. - Pubmed citation
- 7. Wong AE, Sepulveda W. Acardiac anomaly: current issues in prenatal assessment and treatment. Prenat. Diagn. 2005;25 (9): 796-806. doi:10.1002/pd.1269 - Pubmed citation
- 8. Pezzati M, Cianciulli D, Danesi G. Acardiac twins. Two case reports. J Perinat Med. 1997;25 (1): 119-24. - Pubmed citation
Synonyms & Alternative Spellings
|Synonyms or Alternative Spelling||Include in Listings?|
|Acardius twin anomaly||✗|
|Acardius twin syndrome||✗|
|Acardiac twin syndrome||✗|
|Acardiac parabiotic twin syndrome||✗|