Oxford Handbook of Midwifery (26 page)

interview. Pre- and post-test counselling should be offered. The nature
of the test and how she will receive the results is explained.

be considered for the infant of a woman who refuses testing antenatally.
³

1. National Institute for Health and Clinical Excellence (2008). Antenatal care: Routine care for the healthy pregnant mother. Clinical guideline 62. London: NICE. Available at: M
   www.nice.org. uk/cg62.
   
2. Department of Health (2003). Screening for infectious diseases in pregnancy: Standards to support the UK Antenatal Screening Programme. Available at: M
   www.dh.gov.uk (3.5.10).
   
3. Department of Health (2008). UK National Guidelines for HIV testing. London: DH.
   
4. British HIV Association (2008). Management of HIV infection in pregnant women. Available at:
   www.bhiva.org/PregnantWomen2008.aspx (accessed 3.5.10).
   

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   The full blood count
   

   • A full blood count (FBC) obtained in the first trimester acts as a baseline against which all other measurements can be compared.
     
   • A FBC should be repeated at 28 weeks’ gestation to allow for correction of anaemia prior to term.
     
   • As pregnancy progresses, plasma volume expansion is greater than the corresponding rise in the red cell count, this leads to a haemodilution effect and the haematocrit falls, along with the haemoglobin (Hb) level. This is called physiological anaemia.
     
   • Apparent anaemia can be a sign of an excellent adaptation to pregnancy. The effect is greatest at around 30–32 weeks’ gestation.
     
   • Lower mean Hb concentrations are associated with higher mean birth- weights, and higher mean Hb concentrations are associated with an increase in pre-term delivery and low birth-weight babies.
     
   • Hb levels outside the normal UK range for pregnancy should be investigated and iron supplementation considered if indicated.
     
   • The levels are 11g/dL at first contact and 10.5g/dL at 28 weeks’
     gestation.
     
   • In order to correctly assess for anaemia the impact of gestational age
     

     on plasma volume should be considered. Use of haemoglobin level as a sole indicator of anaemia is not recommended.
     

   • Serum ferritin is the most sensitive single screening test to detect adequate iron stores. Using a cut-off point of 30micrograms/L a sensitivity of 90% has been reported.
     ¹
     

     1
     National Institute for Health and Clinical Excellence (2008). Antenatal care: Routine care for the healthy pregnant mother. Clinical guideline 62. London: NICE. Available at: M
     www.nice.org. uk/cg62.
     

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     ABO blood group and rhesus factor: anti-D prophylaxis for the Rh-negative mother
     

     At the initial appointment as well as obtaining a full medical and obstetric history from the woman, venous blood is obtained so that blood group, Rh factor, and the presence of red cell antibodies can be determined. This test will identify women who are Rh-negative and who therefore require further antibody testing during pregnancy.
     

     Recording the blood group is necessary for future reference if the mother needs a blood transfusion around the time of birth. Group O is the most common blood type in the UK; 85% of individuals will also have the Rh factor and will therefore be Rh-positive.
     

     What is the Rh factor?
     

   • The Rh factor is a complex protein antigen carried on the surface of the red blood cell. It is inherited from three pairs of genes called cde/
     

     CDE. It is the pair named D that makes an individual Rh-positive and is
     

     likely to cause Rh iso-immunization.
     

   • Rh-negative women who carry an RhD positive fetus may produce antibodies to the fetal RhD antigens after a feto-maternal haemorrhage. These antibodies may cross the placenta in future pregnancies causing haemolytic disease of the newborn (HDN) if the fetus is RhD-positive.
     
   • HDN can range in severity from stillbirth, severe disabilities, or death, to anaemia and jaundice in the neonate. To prevent this occurring,
     

     Rh-negative women who have experienced a suspected or known sensitizing event during pregnancy are given an intramuscular injection of anti-D immunoglobulin (anti-D Ig) to prevent antibody production.
     

   • The anti-D Ig works by coating the fetal red cells that have escaped into the mother’s circulation so that they cannot be recognized by her immune system. This prevents maternal antibody formation, and thus protects the RhD-positive fetus of any subsequent pregnancy.
     

     What is a sensitizing event?
     

     Very occasionally Rh-negative women may produce antibodies as a result of a mismatched blood transfusion, but fetal red cells from the RhD- positive fetus can cross the placenta and enter the woman’s circulation at any time during the pregnancy, particularly if events cause bleeding from the placental site.
     

     3The most important cause of RhD immunization is during pregnancy where there has been no overt sensitizing event. Sensitizing events include:
     

   • Threatened abortion, and abortion after 12 weeks’ gestation
     
   • Chorion villus sampling
     
   • Threatened abortion, spontaneous abortion, termination of pregnancy
     
   • Amniocentesis
     
   • Antepartum haemorrhage
     
   • Abdominal trauma
     
   • Hypertension
     

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63

In the Rh-negative woman these events should be followed by prophylactic administration of anti-D immunoglobulin. NICE has reviewed the advice that recommends that all Rh-negative women receive prophylactic anti-D.
¹

500IU dose is enough to deal with an 8mL transplacental transfusion
of fetal blood. Prior to 20 weeks’ gestation it is usual to give 250IU as a prophylactic dose.