Manage twin and higher-order multiple pregnancies, including TTTS, sIUGR and single demise

In one line

Chorionicity — not zygosity — drives risk, surveillance and decision-making in multiples; every monochorionic pair shares a placenta and therefore an open vascular circuit, so the consultant's task is to detect the inter-twin transfusion syndromes (TTTS, TAPS, sIUGR) early and to anticipate that demise of one fetus acutely threatens the survivor's brain.

This chapter assumes the multiple pregnancy basics from the Intermediate course (zygosity, the lambda/T-sign, dichorionic surveillance) and spends its words on advanced monochorionic management and its unresolved controversies.

Why this matters in South Africa

The consultant problem in SA is not the diagnosis — it is the geography. Every monochorionic complication is a fetal-therapy problem, and fetoscopic laser is available at only a handful of tertiary units in the country. The clock that matters in TTTS (refer before the dividing membrane is too stuck for the fetoscope, ideally weeks 16–26) collides with district→regional→tertiary referral latency, transport, and bed availability. The judgement is therefore twofold: (1) recognise the monochorionic complication a fortnight earlier than a district sonographer would, because that fortnight is the difference between a laserable placenta and a salvage delivery; and (2) make the right system call — who can be surveilled regionally, who must be referred to the laser centre now, and who is beyond intervention and is simply being timed for delivery. Knowing the Quintero stages counts for little without knowing when to pick up the phone.

Pathophysiology — the shared circuit and its four failure modes

This assumes the placentation groundwork in the Intermediate chapter. Every monochorionic placenta is one organ with one vascular bed crossed by inter-twin anastomoses, and the four monochorionic syndromes are four distinct haemodynamic failures of that single shared circuit. The underlying mechanism is what separates the four — and it dictates the intervention.

• Anastomosis architecture is the master variable. Three connection types coexist on the vascular equator: artery-to-artery (AA), vein-to-vein (VV) and the deep, unidirectional artery-to-vein (AV) connections that run through a shared cotyledon. AV anastomoses are one-way pumps; net transfusion occurs when AV flow in one direction is not balanced by an AA anastomosis (which is bidirectional and pressure-equalising and therefore protective). The presence and calibre of a large AA anastomosis is the single best protector against TTTS and the reason sIUGR type II/III behaves as it does.
• TTTS = a volume/pressure imbalance. Net AV transfusion makes the donor hypovolaemic (oliguria → oligohydramnios → "stuck twin") and the recipient hypervolaemic (polyuria → polyhydramnios). The recipient's volume load drives the renin–angiotensin paradox: the donor's under-perfused kidney releases renin, vasoactive mediators cross to the recipient, and the recipient develops hypertension, myocardial hypertrophy and ultimately a cardiomyopathy with functional/structural right-ventricular outflow obstruction — which is why the sicker heart is in the bigger twin. This is a fluid-and-pressure disease, so the fluid discordance is the diagnostic signal.
• TAPS = a slow, isolated red-cell imbalance through tiny anastomoses. When transfusion occurs only through a few minuscule (<1 mm) AV anastomoses with no compensating AA, the transfer is too slow to shift volume (so liquor stays normal) but chronic enough to make the donor anaemic and the recipient polycythaemic. It is the haemoglobin-without-fluid disease, and it is the classic post-laser complication when a residual tiny anastomosis is left behind. Hence it is screened by MCA-PSV, not by fluid.
• sIUGR = unequal placental sharing. Unequal territorial division of the single placenta starves one twin. The small twin's umbilical-artery waveform — and crucially the behaviour of a large AA anastomosis — defines the Gratacós types and the mode of death (see Assessment). The mechanism is placental real-estate, not transfusion, which is why fluid is usually normal.
• TRAP (acardiac twin) = a reversed, parasitic circuit. Through a large AA (and usually VV) anastomosis present from early development, the "pump" twin perfuses an acardiac, structurally absent co-twin in reverse (deoxygenated blood enters the recipient via its umbilical artery). The pump twin is at risk of high-output cardiac failure and polyhydramnios, not anaemia. Occurs in roughly 1% of monochorionic pregnancies; the threat is to the structurally normal pump twin.

The clinical corollary: a monochorionic placenta cannot be managed as "twice a singleton." Anything you do to one twin (deliver it, let it die, transfuse it) is transmitted through the shared circuit to the other within minutes. This is the unifying reason single demise damages the survivor, reduction must occlude the cord rather than inject the fetus, and laser must be complete.

Assessment

• Chorionicity by 14 weeks is the single most important determination. It is reliable only in the first trimester: the lambda (twin-peak) sign = dichorionic, the T-sign = monochorionic. The SA SAJOG best-practice guideline requires it documented before 13⁺⁶ weeks; after this, membrane-count and fetal-sex inference are unreliable, and an undated "twin pregnancy" referred late should be treated as monochorionic until proven otherwise.
• Label the twins unambiguously (e.g. left/right, or upper/lower relative to a fixed landmark) and keep the mapping for the whole pregnancy — discordance is meaningless if you cannot say which fetus is which between scans.
• Monochorionic diamniotic (MCDA) surveillance is fortnightly from 16 weeks. At each scan: deepest vertical pool in both sacs, bladder visibility, EFW for discordance, umbilical-artery Doppler, and MCA peak systolic velocity (MCA-PSV) to screen for TAPS. Document the donor bladder and stomach.
• Read the pattern, not the single number. TTTS = polyhydramnios/oligohydramnios sequence (DVP >8 cm recipient before 20 wks, or >10 cm after; <2 cm donor) — amniotic-fluid discordance, not size discordance. TAPS = isolated haemoglobin discordance with normal fluid: MCA-PSV >1.5 MoM (anaemic donor) and <1.0 MoM (plethoric recipient), or a delta-MCA-PSV >0.5 MoM. sIUGR = EFW discordance ≥25% with a small twin <10th centile — a growth problem classified by the small twin's umbilical-artery Doppler.
• Higher-order multiples add the chorionicity permutations (a triplet can be DCTA, MCTA, etc.); each monochorionic component carries the monochorionic risks, and fetal reduction/selective-termination counselling becomes part of assessment.

Staging the syndromes — and where each system misleads

Beyond recognising TTTS, the task is staging it correctly, because the stage sets the intervention threshold and the prognosis.

• TTTS — Quintero I–V. Stage I: discordant fluid only, donor bladder still visible. Stage II: donor bladder no longer visible (the watershed — bladder absence means the donor is profoundly oliguric). Stage III: critically abnormal Dopplers in either twin (absent/reversed UA end-diastolic flow, reversed ductus venosus a-wave, or pulsatile umbilical vein). Stage IV: hydrops (usually the recipient, from cardiac failure). Stage V: demise of one or both. The system's well-known weakness is that it is not strictly sequential and not purely prognostic — a pregnancy can present at stage III without passing through II, and recipient cardiomyopathy (the strongest predictor of recipient death) is not captured at all. This is why some centres add a cardiovascular (CHOP-type) score; Quintero remains the common staging language, but recipient cardiac function and cervical length modify the plan independently of stage.
• TAPS — Slaghekke antenatal 5-stage. Stage 1: donor MCA-PSV >1.5 MoM and recipient <1.0 MoM, no other compromise. Stage 2: donor >1.7 MoM and recipient <0.8 MoM, no other compromise. Stage 3: stage 1 or 2 plus cardiac compromise of the donor. Stage 4: hydrops of the donor. Stage 5: demise of one or both preceded by TAPS. Note the asymmetry: in TAPS it is the donor (the anaemic twin) that decompensates and becomes hydropic — the mirror image of TTTS, where the hydropic twin is the recipient. The newer delta-MCA-PSV >0.5 MoM criterion (Tollenaar) improves antenatal detection over the absolute 1.5/1.0 cut-offs and is the modern screening threshold.
• sIUGR — Gratacós I/II/III by the small twin's UA Doppler. Type I: positive UA end-diastolic flow → benign, often deliverable near term. Type II: persistently absent/reversed end-diastolic flow → high risk of deterioration, plan delivery preterm. Type III: intermittently absent/reversed end-diastolic flow (the "iAREDF" pattern), caused by a large AA anastomosis intermittently dumping flow between twins. Type III is the trap: it can look stable for weeks and then cause sudden, unpredictable death of the small twin, with acute exsanguination of the larger twin into the dying small one — the same mechanism as single demise. Type III therefore needs tertiary co-management and a low threshold for steroids, not routine fortnightly scanning.