Insights into the pathophysiology of twin-twin transfusion syndrome.

Twin-twin transfusion syndrome (TTTS) is attributed to trans-anastomotic transfusion between twins. Anastomoses are ubiquitous in monochorionic (MC) placentae, yet TTTS develops in only 15%. Although ex vivo and in vivo studies fail to identify a unique anastomotic signature, TTTS placentae are typically associated with an imbalance in unidirectional arteriovenous anastomoses with absent bidirectional anastomoses. Doppler detection of an artery-artery anastomosis reduces the chance of TTTS, whereas, in those that develop the disease, it improves stage-independent survival. Selective laser is often curative, but an increasingly recognized risk of persistent or reverse TTTS may be attributable to atypical arteriovenous anastomoses not identifiable from the chorionic plate. Simple dysvolaemia fails to explain several phenotypic features, including haematological concordancy, recipient hypertension, and reversibly absent end diastolic flow in the donor. The renin-angiotensin system is upregulated in the donor and downregulated in the recipient's kidneys, while paradoxically raised renin levels in the recipient may contribute to raised afterload along with endothelin. Although research is limited in humans by therapy and the lack of a suitable experimental model, further studies of placental and vascular pathophysiology may not only refine current treatment modalities but may also, in addition, suggest further avenues for downstream management such as genetic predisposition testing or pharmacological intervention.

High risk of unexpected late fetal death in monochorionic twins despite intensive ultrasound surveillance: a cohort study.

BACKGROUND: The rationale for fetal surveillance in monochorionic twin pregnancies is timely intervention to prevent the increased fetal/perinatal morbidity and mortality attributed to twin-twin transfusion syndrome and intrauterine growth restriction. We investigated the residual risk of fetal death after viability in otherwise uncomplicated monochorionic diamniotic twin pregnancies. METHODS AND FINDINGS: We searched an electronic database of 480 completed monochorionic pregnancies that underwent fortnightly ultrasound surveillance in our tertiary referral fetal medicine service between 1992 and 2004. After excluding pregnancies with twin-twin transfusion syndrome, growth restriction, structural abnormalities, or twin reversed arterial perfusion sequence, and monoamniotic and high-order multiple pregnancies, we identified 151 uncomplicated monochorionic diamniotic twin pregnancies with normal growth, normal liquor volume, and normal Doppler studies on fortnightly ultrasound scans. Ten unexpected intrauterine deaths occurred in seven (4.6%) of 151 previously uncomplicated monochorionic diamniotic pregnancies, within 2 wk of a normal scan, at a median gestational age of 34(+1) wk (weeks(+days); range 28(+0) to 36(+3)). Two of the five cases that underwent autopsy had features suggestive of acute late onset twin-twin transfusion syndrome, but no antenatal indicators of transfusional imbalance or growth restriction, either empirically or in a 1:3 gestation-matched case-control comparison. The prospective risk of unexpected antepartum stillbirth after 32 wk was 1/23 monochorionic diamniotic pregnancies (95% confidence interval 1/11 to 1/63). CONCLUSION: Despite intensive fetal surveillance, structurally normal monochorionic diamniotic twin pregnancies without TTTS or IUGR are complicated by a high rate of unexpected intrauterine death. This prospective risk of fetal death in otherwise uncomplicated monochorionic diamniotic pregnancies after 32 wk of gestation might be obviated by a policy of elective preterm delivery, which now warrants evaluation.