Surgery

Criteria for Surgery

Patients are considered for surgery when the pregnancy is between 16 and 26 weeks gestation. 

Further criteria include the following:

• Same sex
• Single placenta
• Minimal fluid in donor (less than 2 cm pocket)
• Too much fluid in the recipient (more than 8 cm pocket)
• Thin dividing fetal membrane
• Prominent bladder in recipient
• Difference in fetal size
• Absence of kidney defect

A patient may not be offered surgery if the following conditions exist:

• Abnormal genetic studies
• Ruptured or detached membranes
• Prior septostomy (purposely making a hole in the dividing membrane)
• Short or dilated cervix
• Pre-term labor
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Risks and Complications

There are potential complications associated with the surgery:

• There is the possibility of bleeding in the mother and/or fetuses, which could prevent the completion of the procedure.
• Rarely, bleeding may be of such magnitude that we may need to make an abdominal incision (laparotomy) and place a suture on the uterus.
• In extreme circumstances it may be necessary to remove the uterus to control bleeding. This would not allow the mother to have any further children. Severe bleeding could result in damage to many organs, brain damage, or even death.
• Preterm labor, amniotic fluid leakage or premature rupture of membranes could occur. If any of these complications occur, we may need to keep the mother in the hospital.
• Infection of the amniotic cavity may also occur and lead to these complications. If infection is diagnosed, delivery is required to prevent further complications.
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There is a low incidence of these complications as precautions are taken to minimize these risks. You will be placed on antibiotics to prevent infection. Very small instrumentation is used to help prevent bleeding and preterm labor. All patients are evaluated thoroughly prior to surgery.

Twin-twin transfusion syndrome (TTTS)

Twin-twin transfusion syndrome (TTTS) arguably presents the greatest challenge in modern day fetal therapy. Firstly, two fetuses are involved. Second, the natural history of fetal loss or damage is extremely high compared to other correctable defects. Thirdly, because the defect is in the placenta, these fetuses are structurally normal, and thus potentially completely salvageable. Finally, TTTS is relatively common, occurring in 10-15% of monochorionic (MC) twins, thus affecting c.1 in 3200 pregnancies, or 1 in 1600 fetuses.

TTTS makes a disproportionate contribution to perinatal morbidity and mortality. It accounts for 17% of perinatal deaths in twins overall, and survivors are at significant risk of long-term neurological damage. Chronic TTTS is attributed to unbalanced net transfusion of blood via placental vascular anastomoses, causing anaemia, growth restriction, oliguric oligohydramnios in the “donor”, and polycythaemia, polyuric polyhydramnios, and circulatory overload in the “recipient”. Mean haemoglobin discordancy in utero is 3.4g/dl, and only exceeds 5g/dl in <25%. Cardiac and renal sequalae may occur in survivors. There is a high incidence of antenatally-acquired neurological lesions in survivors, and c.5-10% will have long-term neurodevelopmental sequalae.

Treatments which have been advocated include digoxin, serial amnioreduction, prostaglandin inhibitors, “give and take” transfusion, sectio parvae, selective fetocide, laser ablation, and septostomy. The length of this list demonstrates how elusive development of optimal therapy has proven. The chief obstacle has been lack of understanding of the underlying pathophysiology. Perinatal survival rates of <20% without treatment have improved to >50% with modern treatments. Some aim primarily to control amniotic fluid volume. Amnioreduction in addition may improve uteroplacental perfusion. Amniotic septostomy, with a survival of 85% in a pilot study, is currently being evaluated in a multicentre RCT. PG synthase inhibitors are contra-indicated because they further impair the donor twin’s renal function. Selective fetocide can now be safely offered due to the development of safe bipolar diathermy techniques. Unlike early work, the recipient may be selected as being both technically easier and less likely to have pre-existing damage. The blitzkrieg laser technique of completely dividing the placental vasculature has achieved comparable survival to amnioreduction in severe cases presenting <28 weeks (c.60%), but has been associated with a high procedure-related loss rate/ procedure failure rate. Comparison of survival distribution suggests that laser leads to more single survivors, but fewer double survivors, and fewer double deaths compared to amnioreduction. Laser has been suggested to reduce the incidence of neurological lesions, although this has yet to be evaluated in controlled studies.

There are two recent developments. The first is tailored therapy, in which the appropriate therapy is selected based on the likely prognosis. Milder cases are treated with amnioreduction/septostomy, and more severe with laser or fetocide. Factors present at presentation associated with a good prognosis are the presence of artery to artery anastomoses, present end diastolic frequencies in the donor umbilical artery, and lack of venous pulsations in the umbilical vein of the recipient. Although laser has the advantage of being a single procedure, the disadvantage is that it requires complex equipment and sepecialised skill. In contrast, the combination of serial amnioreduction with selective fetocide in severe cases is a more widely available therapeutic approach, and theoretically should lead to a survival rate in the region of 75%. The second development is now the subject of intense research. Selective identification and ablation of those few (1-3) deep arteriovenous anastomoses responsible for TTTS avoids destroying healthy cotyledonary vessels, and there is some anecdotal evidence that this reduces the procedure-related loss rate. However, only around 2/3 of AV anastomoses can be identified endoscopically, while early Doppler studies suggest that at least some AV anastomoses can be identified by Doppler study.

The treatment of twin-twin transfusion remains controversial, although better understanding of the underlying physiology is leading to more rational approaches. Poor survival with conservative management has improved from 20% to around 60% with amnioreduction or non-selective laser ablation, while in severe cases selective fetocide by cord occlusion leads to an 85% single survival rate. As a result, prevention of neurodevelopmental sequelae in survivors is assuming greater importance. More rational treatment by selective identification and targeted ablation of the few AV anastomoses mediating the disease with minimal collateral damage is being developed. In addition, selecting treatments by sequential or tailored approaches may optimise survival and reduce handicap rates.