TTTS staging: Following the evidence and improving access to fetal care centers

Dear Editors, We appreciate the editorial by Drs Munoz and Shamshirsaz entitled “TTTS Staging Updates: Balancing Evidence, Access and Patient Care.” We wholeheartedly agree that access to care for patients while minimizing travel to distant Fetal Care Centers is of utmost importance. Our article “Consensus update on twin-twin transfusion syndrome staging: An international Delphi study” suggests using the term “pre-TTTS” for a notable amniotic fluid discordance in monochorionic multiples that does not meet criteria for stage I TTTS (i.e. isolated polyhydramnios, isolated oligohydramnios, or an obvious discordance in amniotic fluid). Our recommendation for increased surveillance (follow-up in less than the typical 2-week screening interval), and for performing Doppler studies, including venous Dopplers, for pre-TTTS aligns with the recommendations set forth in the SMFM Consult series #72 “Twin-twin transfusion syndrome and twin anemia-polycythemia sequence” [1]. Miller et al. [1] note that “concerns that should prompt more frequent monitoring include sonographic suspicion for developing or overt pathology (such as identification of isolated polyhydramnios, subjective oligohydramnios, obvious discordance in amniotic fluid volumes, or Doppler abnormalities).” Several studies support fluid discordance as a risk factor for progression to TTTS [2-4]. A 2024 study [2] demonstrated a rate of progression to TTTS of 41% with a latency period ranging from 12 to 27 days. The median gestational age at the time of laser ranged from 16.9 to 22.5 weeks, suggesting laser surgery was performed shortly after progression to TTTS (rather than with a latency of >100 days). We are proposing enhanced surveillance for 2–4 weeks during the time of highest risk of progression. We suggested the term “atypical TTTS” for cases where cardiac compromise and polyhydramnios in the recipient are present in the absence of severe oligohydramnios in the donor. We do not propose that these cases present without any amniotic fluid abnormalities and do not recommend screening for it in the absence of pre-TTTS. We agree that the diagnosis of TTTS should not require a fetal echocardiogram, due to its limited availability. We purposefully did not consider parameters for inclusion in the staging system that would require advanced cardiac assessment, such as the myocardial performance index. Assessment of the umbilical artery, umbilical vein, middle cerebral artery, and ductus venosus is widely available. The evaluation of tricuspid regurgitation is within the scope of many maternal fetal medicine units outside of specialized fetal centers. At a minimum, evaluation of the umbilical vein is technically straightforward and can serve as a proxy for those units not able to reliably evaluate the ductus venosus or assess for tricuspid regurgitation in triaging which patients require referral to a fetal center. Delphi participants came from geographically diverse backgrounds and included those that practice in fetal centers that require significant travel of their patients and thus had a deep understanding of the financial and social impact. A collaborative approach where regional screening centers have easy access to the expertise of fetal centers via remote sharing of images and telemedicine consultation with fetal intervention specialists has promise to enhance access and provide equitable care to families distant from fetal centers. This approach has been championed at Seattle Children's Hospital, where remote second opinion ultrasound assessment and telemedicine consultations are available to patients in Washington as well as five other Pacific Northwest states to enable local, enhanced screening for pre-TTTS and stage 1 TTTS. Collectively we can ensure access for all our patients while minimizing the financial and travel burden. Bettina Paek has a financial interest in eDoula, a patient education platform. She has served as an expert witness.