When the words ‘identical twins’ strike the mind, phrases like ‘similar faces’ and ‘shared habits ‘ echo. Not only that but also a ‘shared placenta’ during their intrauterine life.



Above images show marked colour asymmetry in the placenta and between the twins’ feet who were born at 31 weeks of gestation. Figure A exhibits the findings of the physical examination of the monoamniotic, dichorionic identical twins, showing a pale first twin and a ruddy second one. Placenta upon analysis (figure B) revealed fragile, pale vessels from the first twin and plethoric blood vessels from the second twin. This is suggestive of twin anaemia polycythemia sequence (TAPS).

TAPS is due to the disproportionate distribution of red blood cells between the twins, one being anaemic and the other polycythemic. TAPS is a form of twin-to-twin transfusion syndrome (TTS).

Monozygotic twins with monochorionic, diamniotic placentation.

Image source: Medscape

What is TTS?

TTTS is the disease of the placenta. It occurs in identical twins who share the placenta (monochorionic). An asymmetry is seen between the blood flow to the twins, with one twin (recipient) receiving the lion’s share, while the donor twin gets hypoperfused.

Since the donor twin is hypoperfused, it weighs 20% lesser, is anaemic and oliguric, whereas the recipient twin is plethoric with a haemoglobin difference of > 5 g/dL.



Since the donor twin is dehydrated, lesser urine is produced hence the low volume of amniotic fluid i.e. oligohydramnios, resulting in restricted fetal growth, and the stuck-twin phenomenon, fixing the donor twin against the uterine wall. Inadequate blood to organs like brain, kidneys may lead to multiorgan failure.

Identical twins with twin-to-twin transfusion syndrome (TTTS)

Image Source: © Children’s Minnesota

Is excess blood/fluid harmful too?

The recipient twin is hypervolemic, forms more urine, hence polyhydramnios. Excess blood can be strenuous for the heart to pump therefore hypertrophic cardiomegaly and ultimately cardiac failure may follow. Other features may include disseminated intravascular coagulation, hydrops fetalis, premature delivery and hyperbilirubinemia postnatally.

A prenatal ultrasound detects a twin pregnancy and also determines the Chorionicity. Special attention is paid to monochorionic, diamniotic pregnancy with more frequent ultrasounds.

The case in the discussion here underwent transabdominal ultrasonography at 30 weeks of gestation when twin anaemia polycythemia sequence (TAPS) was suspected. Another ultrasound 6 days later revealed oligohydramnios and polyhydramnios in the first and second twin respectively, indicating twin-to-twin transfusion syndrome (TTTS). Postnatally, haemoglobin levels were checked. A level of 6.9 g/dL was recorded in the donor (pallid) twin and 25.5 g/dL in the recipient (plethoric) twin.

Treatment options include:



– Amnioreduction i.e. draining the amniotic fluid from the recipient twin. This is the most common.

– For severe cases, fetoscopic laser photocoagulation is reserved. It is performed between 16 to 26 weeks of gestation to ablate the shared blood vessels between the twins.

– Cord Coagulation is the last resort, performed only when the donor twin has no chances of survival. It is done to cut off blood supply to the donor twin to maintain supply to the recipient.



Unfortunately, without treatment, approximately 70–80% of twins with TTTS will die. Even the death of one twin negatively affects the surviving twin, due to redirection of blood supply towards the deceased twin

The twins in the discussion here were treated postnatally. Donor twin received packed cell transfusion and recipient underwent phototherapy and exchange transfusion. Both were discharged after 39 days. At the 12-month follow-up, normal development was reported.





References

– (2020). Retrieved from The Twin to Twin Transfusion Syndrome Foundation.

– Terence Zach, M. (2018, August 03). Twin-to-Twin Transfusion Syndrome. Retrieved from

Medscape.

– Twin-to-Twin Transfusion Syndrome. MedlinePlus. 9/26/2015

– Joana Araújo Pereira, M. a. (February 6, 2020). Twin Anemia Polycythemia Sequence. The

New England Journal of Medicine, N Engl J Med 2020; 382:e9. DOI:

10.1056/NEJMicm1905895