Diagnostic Criteria of TTTS
for Medical Professionals
The following extracts from medical publications are provided for the information of doctors, consultants, midwives, sonographers, and radiologists to aid with the diagnosis of twin to twin transfusion syndrome.
Diagnosis needs to be followed by urgent referral to a centre experienced in the treatment of TTTS.
" Current Thoughts on Twin-Twin Transfusion Syndrome"
Robert B. Cincotta, FRACOG, MD. & Nicholas M. Fisk, FRACOG, PhD
Royal Postgraduate Medical School, Institute of Obstetrics & Gynecology,
Queen Charlotte's Hospital, London, United Kingdom.
Published June 1997, Clinical Obstetrics & Gynecology, © 1997 Lippincott-Raven Publishers
Women with TTTS present in the second trimester of pregnancy with a sudden increase in abdominal girth, extreme discomfort, and occasionally respiratory distress or preterm labor. Abdominal examination shows tense polyhydramnios.
The required ultrasound (US) criteria are monochorionicity, a marked discordance in amniotic fluid volume between the twins (known as the oligo/polyhydramnios sequence), and a discordance in size with the larger twin in the polyhydramniotic sac. Monochorionicity is most accurately diagnosed in the first trimester by the lack of chorion between the two amniotic sacs of the two twins. and/or the presence of only a single extra-embryonic coelom. However, chorionicity determination is less accurate in the second trimester when TTTS presents; absence of the lambda sign and a thin intertwin membrane in like sexed twins is then suggestive, but not diagnostic of, monochorionicity. The commonest US appearance of TTTS is gross polyhydramnios in one sac with a recipient twin who has a large bladder and a smaller donor twin who has an empty bladder that appears stuck against the wall of the uterus in its oligohydramniotic sac (the so-called 'stuck twin'). It can be difficult to visualise the intertwin membrane, such that TTTS is sometimes misdiagnosed as monoamniotic twins. ... The recipient twin may show signs of hydrops, although less commonly the donor twin may also become hydropic. The recipient often has an enlarged heart with a thickened poorly contractile myocardium.
" Opinion - Monochorionic twin pregnancies: 'les liaisons dangereuses' "
Dr. Yves Ville,
Director Fetal Medicine, St. George's London
Ultrasound obstet. Gynecol. 10 (1997) 82-85, © 1997
There is still little agreement on the definition of TTS. The most commonly accepted criterion to describe twin-twin transfusion syndrome presenting in the mid-trimester is the discordancy in amniotic fluid volume. This can be very inaccurate unless oliguria and oligohydramnios develop in the donor, and polyuria with subsequent severe polyhydramnios (deepest pool > 8 cm) can be demonstrated in the recipient. The discrepancy in size is frequent but not mandatory; both fetuses are of the same sex and the pregnancy might be known to be monochorionic. Although placental mapping of the anastomotic vessels does not seem clinically relevant, the demonstration of cardiac overload or congestive heart failure in a recipient twin should be an essential diagnostic criterion of the syndrome.
" Management of Severe Twin to Twin Transfusion Syndrome "
Professor K. H. Nicolaides,
Harris Birthright Research Centre for fetal Medicine,
King's College Hospital School of Medicine, London, UK
The diagnosis of severe twin to twin transfusion syndrome is based on the ultrasound findings of a monochorionic diamniotic twin pregnancy with fetuses that are discordant in size. The larger twin (presumed recipient), has a distended bladder and is surrounded by polyhydramnios, whereas in the smaller twin (presumed donor) the bladder is always empty and the fetus appears to be fixed to the placenta or the uterine wall because of anhydramnios.
DOPPLER ULTRASOUND FINDINGS
Doppler studies in severe twin-twin transfusion syndrome presenting with acute polyhydramnios during the second trimester of pregnancy have demonstrated that (i) in both the donor and recipient resistance to flow in the umbilical artery is increased and in the recipient the increase is greater (ii) in both the donor and recipient blood flow velocity in the thoracic aorta is decreased, but in the donor the decrease is greater before 21 weeks whereas the opposite is true for the recipient, and (iii) in the middle cerebral artery resistance to flow is higher and blood flow velocity is lower in the donor than in the recipient.
Professor Geoffrey A Machin, M.D.
Department of Pathology
The Permanente Medical Group
280 West MacArthur Boulevard
Oakland, CA 94611, USA
Professor Geoffrey Machin has worked on twin pregnancy problems in Britain, Canada, and the USA. He has written several papers and textbook chapters on particular problems of monochorionic twins.
Professor Machin writes:
"Although the ultrasound diagnosis of well-advanced antenatal TTTS can be made, it is often already too late to plan and carry out treatment that can be fully effective and leave the twins intact, ie. without organ damage. The best way to achieve real progress with this disease is to catch it early. At the time of the first ultrasound exam, it is easy to make the distinction between DC and MC twins, judged by the the thickness of the septal membranes. Too often, the ultrasound report says thet there are 'two sacs' or that membrane thickness is 'indeterminate'. A little extra effort and a forthright attempt to decide between DC and MC will have the following good effects. 1) Parents of DC twins can be strongly reassured that their twins will not develop TTTS. 2) MC twins can be followed very carefully at 2 week intervals for the earliest signs of onset of TTTS (ie. oligohydramnios/polyhydramnios). This will gain valuable time during which the treatment can be tailored to each case, after full discussion with the parents.
If necessary, expectant parents of twins should insist, from earliest stage of pregnancy, that the chorion status of the fetuses be determined accurately, and that the parents must be given this information."
Professor Machin is the co-author of a new book on twins to be published in Spring, 1998: "An Atlas of Multiple Preganancy. Biology and Pathology", Parthenon Press, London and New York. The book is intended for health care professionals and for concerned parents with a good biological sciences background.