Twin Anaemia-Polycythaemia Sequence

Twin anaemia polycythaemia sequence is a chronic, slow, unbalanced blood transfer between monochorionic twins through very small connecting vessels, leaving one twin anaemic (donor) and the other polycythaemic (recipient), without a difference in amniotic fluid. It occurs spontaneously or after laser treatment for twin to twin transfusion syndrome. It matters because it causes fetal and neonatal brain injury, stillbirth and neonatal haematological problems.

• Risk factors: monochorionic twin placentation, previous laser treatment.
• Donor has anaemia with raised reticulocytes; recipient has polycythaemia and risk of clots.
• It is diagnosed by Doppler and not by liquor volume.

Women are asymptomatic. The pregnancy shows no polyhydramnios or oligohydramnios, and the twins may have similar or different growth. Some have reduced fetal movements.

• Normal liquor in both sacs.
• Donor placenta pale and thick, recipient placenta dark, at birth.
• Differential diagnosis: twin to twin transfusion syndrome, selective growth restriction, twin discordance from other causes, fetal anaemia from alloimmunisation or parvovirus, fetal heart disease.
• Complications: donor anaemia, hydrops, fetal death, recipient polycythaemia and thrombosis, brain injury in either twin, preterm birth, neonatal haematological complications.

The approach is middle cerebral artery Doppler of both twins.

• Middle cerebral artery peak systolic velocity above 1.5 multiples of the median in the donor and below 1.0 multiples of the median in the recipient confirms the diagnosis.
• Staging: stage 1 (donor above 1.5, recipient below 1.0); stage 2 (donor above 1.7, recipient below 0.8); stage 3 (donor cardiac compromise); stage 4 (donor hydrops); stage 5 (death of one or both).
• Placental ultrasound for differing echo texture; growth and amniotic fluid index; umbilical artery Doppler.
• After birth: haemoglobin difference above 8 g/dL, reticulocyte ratio above 1.7, and placental dye injection.

The principle is staged treatment by gestation, from observation to laser or transfusion, and delivery at the stage specific time.

• Supportive: refer to a fetal medicine unit; scans with Doppler every week; daily fetal movement counts; birth in a unit with neonatal intensive care.
• Pharmacological: betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days before planned delivery; magnesium sulphate 4 g IV over 20 minutes then 1 g per hour until delivery for 24 hours at most before 32 weeks; newborn donor: O negative packed red cells 10 to 20 mL/kg IV over 3 to 4 hours; newborn recipient: partial exchange transfusion with sodium chloride 0.9 percent if venous haematocrit is above 65 percent, volume (mL) = blood volume (80 mL/kg) x weight x (observed minus desired haematocrit of 55) divided by observed haematocrit, and hydration; oxytocin 10 IU IM at birth.
• Procedures: fetoscopic laser coagulation of the connecting vessels in a fetal medicine unit (preferred where available); intrauterine transfusion for the donor, with or without partial exchange of the recipient; selective feticide for severe disease; expectant care with Doppler every week for stage 1; delivery at 34 to 36 weeks for stage 1 or 2, earlier for stage 3 or above.
• Red flags: hydrops, cardiac compromise in the donor, fetal death, abnormal cardiotocography, worsening Doppler.
• Follow-up: Doppler every week to every 2 weeks; newborn haemoglobin, reticulocytes, haematocrit and bilirubin at birth and daily for 3 days; cranial ultrasound and neurodevelopment review at 2 years.