PRENATAL DIAGNOSISPrenat Diagn 2008; 28: 559–560.Published online in Wiley InterScience(www.interscience.wiley.com)

CORRESPONDENCE

Twin anemia-polycythemia sequence (TAPS) without a cause

We read with great interest the article on an intriguingcase of isolated fetal anemia in a recipient twin afterlaser treatment for twin-to-twin transfusion syndrome(TTTS) and congratulate the authors on the thoroughinvestigation and detailed description of the case (Ishiiet al., 2008). We agree with the authors that this casedoes not fulfill the criteria for twin anemia-polycythemiasequence (TAPS) as no polycythemia was detectedin the co-twin (Lopriore et al., 2007a). Moreover, noresidual anastomoses were found on placental injection,a prerequisite for TAPS (Lopriore et al., 2007a).

We would appreciate the opportunity to add just afew thoughts on the possible cause of anemia in theex-recipient and discuss the differential diagnosis.

The authors suggest that anemia may have beencaused by an acute intraoperative feto–fetal exsanguina-tion because of the sequential selective laser coagulationof the anastomoses. However, we have recently shownthat, in vitro, with computer modeling, increased ery-thropoiesis in an anemic ex-recipient should correct theacute anemia within a week after laser treatment (vanGemert et al., 2008b). In the present case, severe ane-mia was still present six weeks after laser, and even fourweeks after the intrauterine blood transfusion, whichsuggests persisting chronic blood loss instead of acuteperioperative blood loss.

Two alternative explanations may then be envis-aged. First, as recently described by our group, spon-taneous thrombosis of a small residual anastomosis mayhave led to subsequent resolution of TAPS (Loprioreet al., 2008a). In the latter case, spontaneous deliv-ery occurred at almost 36 weeks’ gestation, whereas inthe present case, gestation was suddenly interrupted at33 weeks’ gestation because of abruptio placenta. Thiscould explain why fetal anemia may have had time toresolve completely in our case, but was still presentin the Ishii case. A second, and more likely possibil-ity, is that there may have been an undetected residualanastomosis. Residual anastomoses after laser surgeryare not uncommon and are often very small (diame-ter <1 mm). These may therefore be difficult to detect(Lopriore et al., 2007b). The patent anastomosis maythen have led to a mild form of TAPS, without poly-cythemia in the ex-donor. In the reported case, thelarge inter-twin difference in reticulocyte count (6.8%vs 3.8%) count is, suggestive of a small, but persist-ing inter-twin feto–fetal transfusion (Ishii et al., 2008).The unique placental injection technique used by theauthors (placental vascular casting) may explain whya small anastomosis could have been missed. Placen-tal vascular casting is ideal for detection of deep-hiddenanastomoses that occur underneath the placental surface.However, the downside of this technique is that small

anastomoses may break easily (van den Wijngaard et al.,2007). Whether a small anastomosis was patent in thiscase but broke because of the casting technique, cannotbe proved nor ruled out.

Nevertheless, there is an indirect way to determinewhether a patent anastomosis may have been missed.The trick is to measure the adult hemoglobin concentra-tion in the new recipient at birth. As the intrauterineblood transfusion is administrated to the new donor,presence of adult hemoglobin in the new recipient is anirrefutable evidence of feto–fetal transfusion through apatent anastomosis. We recently discussed this issue in asimilar TTTS case treated with intrauterine blood trans-fusion after incomplete laser (Lopriore et al., 2007c). Inanother case report, measurement of adult hemoglobinafter birth also allowed us to determine the inter-twintransfusion rate (Lopriore et al., 2008b). Details of theequations required for the calculations are reported else-where (van Gemert et al., 2008a).

In this specific case, it would be very interesting toknow whether the authors also determined the concentra-tion of adult hemoglobin in their reported case. Regard-less of these issues, we fully agree with the authorsthat further research is required to unravel the causeof fetal hematological complications, which often occurafter laser surgery. A crucial prerequisite for furtherenhancement of our understanding of the complex patho-physiology of iatrogenic TAPS and/or isolated anemiaafter laser surgery, is the accurate description of suchcases, as presented by the authors (Ishii et al., 2008).

Enrico Lopriore1, Dick Oepkes2,Jeroen P. H. M. van den Wijngaard3,Martin J. C. van Gemert3,Johanna M. Middeldorp2 andFrank P. H. A. Vandenbussche21Division of Neonatology, Department of Pediatrics, LeidenUniversity Medical Center, Leiden, The Netherlands2Division of Fetal Medicine, Department of Obstetrics,Leiden University Medical Center, Leiden, The Netherlands3Laser Centre and Department of Obstetrics, AcademicMedical Centre, University of Amsterdam, AmsterdamDOI: 10.1002/pd.2011

REFERENCES

Ishii K, Murakoshi T, Hayashi S, et al. 2008. Anemia in a recipienttwin unrelated to twin anemia-polycythemia sequence subsequentto sequential selective laser photocoagulation of communicatingvessels for twin-twin transfusion syndrome. Prenat Diagn 28:262–263.

Lopriore E, Middeldorp JM, Oepkes D, Kanhai HH, Walther FJ,Vandenbussche FP. 2007a. Twin anemia-polycythemia sequence

Copyright 2008 John Wiley & Sons, Ltd.

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in two monochorionic twin pairs without oligo-polyhydramniossequence. Placenta 28: 47–51.

Lopriore E, Middeldorp JM, Oepkes D, Klumper FJ, Walther FJ,Vandenbussche FP. 2007b. Residual anastomoses after fetoscopiclaser surgery in twin-to-twin transfusion syndrome: frequency,associated risks and outcome. Placenta 28: 204–208.

Lopriore E, van den Wijngaard JP, Middeldorp JM, et al. 2007c.Assessment of feto-fetal transfusion flow through placental arterio-venous anastomoses in a unique case of twin-to-twin transfusionsyndrome. Placenta 28: 209–211.

Lopriore E, Hecher K, Vandenbussche FP, van den Wijngaard JP,Klumper FJ, Oepkes D. 2008a. Fetoscopic laser treatment of twin-to-twin transfusion syndrome followed by severe twin anemia-polycythemia sequence with spontaneous resolution. Am J ObstetGynecol 198: e4–e7.

Lopriore E, van den Wijngaard JP, Pasman S, et al. 2008b.Quantification of feto-fetal transfusion rate through a singleplacental arterio-venous anastomosis in a monochorionic twinpregnancy. Am J Obstet Gynecol, Submitted.

van den Wijngaard JP, Lopriore E, van der Salm SM, et al. 2007.Deep-hidden anastomoses in monochorionic twin placentae areharmless. Prenat Diagn 27: 233–239.

van Gemert MJ, van den Wijngaard JP, Lopriore E, Pasman S,Vandenbussche FP. 2008a. Arterio-venous flow between mono-chorionic twins determined during intra-uterine transfusion. PhysMed Biol 53: 109–117.

van Gemert MJ, van den Wijngaard JP, Lopriore E, Lewi L,Deprest J, Vandenbussche FP. 2008b. Simulated sequential lasertherapy of twin-twin transfusion syndrome. Placenta, Accepted.

Copyright 2008 John Wiley & Sons, Ltd. Prenat Diagn 2008; 28: 559–560.DOI: 10.1002/pd