Monochorionic multiple gestations
MC twins are at substantially increased risk of adverse outcomes
compared to DC twins,44 secondary to typical
angioarchitecture of a monochorionic placenta.45Vascular anastomoses maintain a dynamic bidirectional flow between the
co-twins. Unique complications such as twin-to-twin transfusion
syndrome, twin reversed arterial perfusion sequence, selective
intrauterine growth restriction or discordant malformations are
encountered in monochorionic gestations due to altered vascular
connections. When one of the twins suffers major structural anomaly or
shows doppler patterns suggestive of impending demise, ST of the
specific fetus is the only therapeutic option available to optimize the
survival of co-twin. In case of intrauterine demise of one fetus,
co-twin may acutely exsanguinate across vascular anastomoses and die or
suffer neurological damage in 30-50% cases.46
ST using various vaso-occlusive techniques that completely occlude flow
through the targeted fetus’s umbilical cord have been
developed.47 Initial attempts were made with cord
ligation or cord embolization with thrombogenic coils or sclerosants.
These were often complicated by method failure and high pregnancy
loss-rates. Presently techniques used are namely bipolar cord
coagulation (BCC), laser cord coagulation, radiofrequency ablation
(RFA), microwave ablation and High Intensity Focussed Ultrasound to
achieve selective termination. The main complications associated with
these interventions are preterm rupture of membranes (PPROM), hemorrhage
and PTB.
Bipolar cord coagulation is the standard procedure for ST in
monochorionic pregnancies. Under ultrasound guidance, a 3mm port is
inserted into the sac of the affected fetus and a bipolar coagulation
forceps is passed and used to grasp the cord of the affected fetus which
is coagulated using bipolar energy between 20 and 50W. This technique
simultaneously obliterates the umbilical arteries and vein, causing
immediate cessation of flow and thus preventing any interfetal
hemorrhage. Overall survival rates for co-twin are between 76% and 88%
with low risk of neurological damage (2.6%).48-50
Radiofrequency ablation uses a 17G radiofrequency electrode to generate
high-frequency sinusoidal current (400–500 kHz) which induces local
tissue ionic agitation resulting in frictional heat to cause thermal
coagulation. Under ultrasound guidance, using local anesthesia RFA
needle is inserted into the fetal abdomen at the level of cord
insertion, guided by color Doppler mapping. Radiofrequency energy is
applied until there is ‘roll-off’. Tissue necrosis results in increased
tissue impedance that prohibits the passage of electrical current, hence
there is a drop-in power output indicated as roll-off. Coagulative
damage is usually restricted to 2cm area around the needle tip. Commonly
used devices include LeVeen RFA probe (Boston Scientific, Natick, MA),
Starburst SDE_ radiofrequency needle (Angiodynamics, Inc., Queensbury,
NY, USA) and Covidien Cool-tip™ RF ablation system (Medtronics) Each
function slightly differently, but the net effect achieved is the same.
Occlusion of blood flow occurs slowly only once adequate power has been
applied to achieve tissue desiccation. This may result in an increased
risk of thermal damage to membranes and co-twin demise due to acute
exsanguination.
Fetoscopically guided Nd:YAG laser coagulation of the cord or the
vessels at the route of the cord has been used for ST in MC gestations.
A 400–600-micron laser fiber positioned under ultrasound guidance in
the fetoscope and is advanced a few millimeters beyond the tip of the
needle into the target tissue. Power is applied in short bursts until
the blood flow stops. Coagulation occurs slowly only once adequate
thermal energy is applied often requiring multiple applications of
laser. Slower occlusion again increases the risks for co-twin.
Newer techniques employed are microwave ablation or High frequency
focused ultrasound (HIFU). A thin microwave antenna is placed directly
into the fetus using ultrasound guidance. This antenna emits an
electromagnetic wave through its exposed, non-insulated tip which
agitates water molecules in the surrounding tissue, producing friction
and heat, thus, inducing cellular death via coagulation
necrosis.51 The antennae are internally cooled with
either room-temperature fluid or carbon dioxide to reduce conductive
heating and to prevent possible skin damage.
Modality of HIFU has been used to manage TRAP sequence
cases.52 This technique involves the transmission of a
beam of ultrasound through solid tissue which is focused within the
fetus, enabling thermal coagulation necrosis. The chief advantage lies
in being truly non-invasive. However only a few reports are published
and in one of them the co-twin was delivered with
pseudoarthosis52, and the role of ultrasound beam is
not clear. The procedure required several attempts to achieve complete
occlusion, thus leaving the potential for transfusion-related
complications.
Rossi et al50 presented a systematic review of 345
complicated MC twins who underwent ST. Overall survival rate is almost
similar for BCC (82%) or RFA (86%). Nearly 22% had PPROM and in
one-sixth of cohort, co-twin demise was reported. Roman et
al49 also showed no clear superiority of any one
technique in their comparative series.
Bebbington53 reported that BCC was associated with a
higher rate of overall survival (85.2% v 70.7%) compared to those who
had RFA for ST. The difference was attributed to an increased survival
rate of the co-twin below 28 weeks (BCC 31.6% Vs RFA 10.5 %) probably
as there was a complete cessation of blood flow in BCC cases whereas, in
RFA, there is slow cessation.
O’Donoghue54 reported outcomes for the use of
interstitial laser in ST of thirty MC pregnancies. Overall perinatal
survival was reported in 68% cases. Two of 26 neonates (8%) were
diagnosed with aplasia cutis congenita. They postulated that the
procedure-related losses may be related to difficulty in maintaining the
correct position of the laser fibre during repeated laser applications.
However, Jennifer55 demonstrated laser cord occlusion
is a reasonable surgical modality for ST in their retrospective review
with high PPROM (32.6%) and co-twin survival rates (95.3%).
Meng et al56 described their preliminary novel
experience in the application of microwave ablation for ST and reported
it to be safe and effective. None of the surviving co-twins had evidence
of thermal injury or neurological abnormalities and the overall survival
rate was 73.3% (n=33/45).
All techniques for ST are associated with some risk of co-twin demise
and complications such as miscarriage, PPROM, preterm birth, etc. (Table
1). Each of ST technique has its own merits, no single perfect technique
exists to manage complicated MC gestations. No randomized control
studies are available to assess the superiority of one method over
others, the evidence is though available through various systematic
reviews and metanalyses. The balance between benefits and risks with
these procedures is not always completely clear and the decision is
usually based on technical considerations, local experience, available
instrumentation and above all parental wishes.
Conclusion: Management of multifetal pregnancies is challenging
due to the associated high rates of complications. MFPR aims to increase
the likelihood of a successful pregnancy and the best current means of
evading undesired sequelae of extreme prematurity associated with
high-order multiples. Selective termination for anomalies in multifetal
pregnancies has significantly advanced with acceptable low
procedure-related loss rates. Couples should be provided balanced
counseling about benefits and risks associated with these fetal
interventions so that they can make informed choices for their
pregnancy.
Conflict of Interest: All authors declare that there are no
conflicts of interest.
Contribution to authorship: AB did the literature search and
wrote the article. YSH gave expert opinion and contributed to the
conclusion. All authors approved the final version.
Funding Information: No funding was obtained for this study.