Measurement of middle cerebral artery peak systolic velocity. This is an ultrasound image of the fetal head, taken in transverse section at the level of the base of the skull. Colour Doppler has been used to visualize the circle of Willis, and the two middle cerebral arteries (MCAs) can be seen. The Doppler gate has been placed close to the origin of the MCA from the circle of Willis, and an angle correction has been applied to ensure a true reading of the velocity of blood flow.
Following transfusion, the MCA peak systolic velocity measurements can again be used to assess the degree of anaemia and plan subsequent transfusions. MCA peak systolic velocity measurements are useful for all causes of anaemia, including Kell alloimmunization and anaemia due to non-alloimmune causes, e.g. parvovirus.
Late signs which may be seen on ultrasound suggestive of established severe disease include increased liquor volume, scalp oedema, ascites, pleural effusions and a pericardial effusion.
Cordocentesis and intrauterine transfusion
If the fetus is suspected to be severely anaemic, then the treatment options are intrauterine transfusion or delivery and neonatal treatment (phototherapy, transfusion or exchange transfusion). The choice will depend mainly on the gestation of the pregnancy and to some extent the ease or difficulty of in-utero transfusion in that particular woman.
Intrauterine transfusion should only be performed in tertiary fetal medicine centres. Prior to the transfusion, prophylactic steroids may be given to promote fetal lung maturity, if the pregnancy is at an appropriate gestation. Blood is specially prepared for in-utero transfusion. It is CMV-negative, leucodepleted, irradiated and highly concentrated to reduce the volume which needs to be transfused into the fetal circulation.
Initially, cordocentesis enables accurate determination of fetal haemoglobin. It is usually performed at a point where the cord is static, ideally the placental cord insertion. Sometimes this is not possible because of placental location and fetal lie, and then the fetal umbilical cord insertion can be used, with injection of neuromuscular blocking drugs to the fetus to temporarily stop fetal movement if necessary.
Once the initial sample has been taken the cordocentesis needle is left in position in the cord, and the donor blood is transfused. The amount of blood required depends on the result of the haemoglobin/haematocrit of the fetus, the haematocrit of the donor unit and the gestation of the pregnancy. There is obviously a larger fetoplacental blood volume at later gestations, and larger volumes of donated blood are needed.
Following transfusion, the needle is flushed with saline and a further sample is taken to assess the post-procedure haemoglobin and haematocrit. The aim is to get the post-transfusion fetal haematocrit to 45%.
The timing of subsequent transfusions can be judged by monitoring fetal MCA Dopplers. Usually there is a need to transfuse approximately 2 weeks later, and transfusions are often continued up to 34 weeks, when delivery of the fetus can be considered.
Potential complications which can be encountered include:
technical difficulties – especially posterior placenta or obese woman
cord haematoma
haemorrhage
bradycardia
1% fetal loss
preterm delivery
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
