Maternal Antibodies – Implications for the fetus/neonate BY: Nicole Stevens

Maternal antibodies During pregnancy some maternal antibodies can cross the placenta and enter fetal circulation This is necessary to help with immunity in the newborn while their immune system is developing A downside to this is that the antibodies target fetal RBC’s, and if there is an incompatability it can cause HDN (hemolytic disease of the newborn)

Blood types ABO blood groups discovered first (around 1900) Rh blood types discovered in 1940 (named after the rhesus monkeys because they were used in the research) There are 45 different antigens on the surface of red cells that make up the Rh group Greatest problem with the Rh group is an incompatability between a mother and fetus; best known example of this occurring is when the mother is Rh –ve and the fetus is +ve If the father is +ve, there is a 50% chance of Rh+ve children, if he is negative there is zero chance of an incompatability

Blood types Indentifying someone as Rh+ve or –ve is a simplification There are many variations of the Rh blood types depending on which of the 45 antigens are present The most important of these antigens for mother-fetus incompatability and transfusion problems are D, C, c, E, and e. When a person is identified as being Rh+ve or –ve it is usually in reference to the D antigen Eg: the individual is RhD+ or RhD-

Other Rh blood groups you may have heard of: Kell blood group (anti-K and anti-k) Kidd blood group (anti-Jka and anti-Jkb) Duffy blood group (anti-Fya) MNS and s blood group antibodies These are less common causes of hemolytic disease of the newborn

Routine antenatal screening The ABO and RhD group of all pregnant women should be determined when they first attend for antenatal care. The mothers blood group should also be tested for atypical IgG red cell antibodies, as these may also cause HDN If antibodies are detected, the levels should be monitored frequently throughout the pregnancy in case they increase in titre Rising levels are likely to indicate HDN developing in the fetus Amniocentesis and the level of bilirubin in the amniotic fluid will give a clearer guide to the severity of the disease Involve a paediatric team in the management decisions around early delivery and immediate postnatal care (blood tests, nursery admission etc)

ABO incompatability Beware the “O” group mother The O group mothers serum will contain naturally occuring anti-A and anti-B which means they will potentially attack the RBC’s of an A, B or AB group baby This incompatability is usually less severe than Rh incompatability because fetal RBC’s express less of the ABO blood group antigens compared with adult levels, and they are expressed by other tissues as well as the RBC’s.

First pregnancy v’s subsequent in the Rh-ve mother Not usually incompatability issues with the first pregnancy in the Rh-ve mother, it is the subsequent ones that pose a risk, and that risk increases with each pregnancy During pregnancy nutrients and maternal IgG antibodies cross the placenta into the fetus (but usually the RBC’s don’t – except in the case of placental rupture) Normally anti Rh+ve antibodies don’t exist in the first time mother (except if she has come into contact with Rh+ve blood).

Rh-ve mother At birth fetal blood usually gets into the maternal system, and if the baby is Rh+ve this will stimulate the maternal system to make antibodies to Rh+ve blood antigens. This will create problems for the next pregnancy if the fetus is Rh+ve This problem can be prevented by administering anti D at key points during a pregnancy, following a miscarriage, an ectopic pregnancy, an APH and within 72 hours after the birth. The antiD ‘mops’ up any Rh+ve cells in the maternal circulation, hence reducing the production of antibodies against them.

Hemolytic disease of the newborn (HDN) Used to be a major cause of fetal loss and death in newborns prior to the 1950’s It was around that time that it was discovered that maternal antibodies were attacking fetal red blood cells; this process begins inutero In the 1960’s trials commenced testing the use of therapeutic antibodies that could remove the antibodies from maternal circulation that were causing HDN. Hemolysis is the process of breakdown of RBC’s. Increased rate of hemolysis happens in HDN.

Hemolytic disease of the newborn In HDN mothers produce IgG red rell antibodies, which can cross the placenta and destroy the babys RBC’s. The antibodies that cause HDN are directed against antigens on the babys RBC’s that are inherited from the father but absent in the mother. The mother may develop these antibodies if fetal red blood cells cross the placenta (fetomaternal hemorrhage) during pregnancy or delivery In severe cases babies may die inutero, need inutero transfusions, or be born with severe anaemia requiring transfusion

Hemolytic disease of the newborn The old saying “Kell Kills” comes from the interesting fact that anti-Kell antibodies result in anaemia in the neonate by suppressing marrow erythroid activity, rather than an increased rate of hemolysis.

HDN Life span of RBC’s and increased hemolysis Bi product of broken down RBC’s = bilirubin Increased hemolysis causes aneamia Sympton management, buy time while the underlying problem clears

Managing the neonate Notify paediatric team of admission of mother (prior to delivery) Make a plan for the neonate after birth Likely to involve taking of cord blood for Group, coombs, SBR and FBE Depending on results and level of risk baby may be admitted to SCN ASAP If indicated commence phototherapy Monitor SBR levels 4 – 6 hourly until stable Escalate treatment if SBR levels rise despite maximising treatment

Management of Neonate Maximising phototherapy is achieved by increasing the number and/or strength of lights and the surface area of the baby exposed to them. In these cases, during the early treatment this will mean nappies off and not coming out for feeds. Stay will generally be days, sometimes weeks so parents need to be prepared for this Phototherapy treatment is often stopped and started several times while waiting for the maternal antibodies to clear Blood transfusions and administration of intragam may be part of the management if severe aneamia results.

Reference List http://anthro.palomar.edu/blood/Rh_system.htm http://www.ncbi.nlm.nih.gov/books http://www.transfusion.com.au/disease_therapeautics/fetomaternal/HDN