In the first stage of labour, pain is transmitted via
the spinal nerves of T10–L1 and results from uterine
contractions and dilatation of the cervix. In the second
stage, stretching of the pelvic ligaments causes pain via the
pudendal nerve originating from the S2–S4 nerve roots.

The contraindications/Cautions are-

• Known bleeding disorder (e.g. haemophilia, von Willebrand’s disease or acquired coagulopathy)
• Active antenatal or postpartum bleeding
  - Women considered at increased risk of major haemorrhage (e.g. placenta praevia)
  - Thrombocytopenia (platelet count < 75 × 109/l)
  - Acute stroke in previous 4 weeks (haemorrhagic or ischaemic)
  - Severe renal disease (glomerular filtration rate [GFR] < 30 ml/minute/1.73m2)
  - Severe liver disease (prothrombin time above normal range or known varices)
  - Uncontrolled hypertension (blood pressure > 200 mmHg systolic or > 120 mmHg diastolic)
•  ( In case of any doubt, a haematologist review should be sought)

Pregnant women with red cell antibodies, who are assessed as being at high risk of requiring a blood transfusion, should have a cross-match sample taken at least every week.

Current BCSH guidelines require a sample no more than 72 hours old for providing compatible blood in
pregnancy,but do allow a deviation to the 3-day rule for individual cases such as high-risk women with placenta praevia without red cell antibodies where weekly samples can be taken, as long as a risk assessment is made and recorded in each individual case

In high-risk women with red cell antibodies where a sample every 72 hours is not feasible, a sample should be taken once a week and if transfusion is required a new sample should be taken immediately, to exclude new antibody development. However, in the event of life threatening haemorrhage, urgent transfusion should not be delayed and close liaison with the hospital transfusion laboratory is vital.

Women are generally advised to wait for at least 2 years after treatment for breast cancer before
conception.

Codeine is converted to active metabolites, mainly morphine. The ultrarapid metaboliser phenotype is due to duplications of the CYP2D6 gene, and prevalence varies by ethnic origin.

Ultrarapid metabolisers who take codeine can have up to 50% higher plasma concentrations
of its active metabolite morphine than extensive metabolisers, with the consequence that there is a risk of serious toxicity even at therapeutic doses of codeine in such individuals.

Genotyping can be undertaken from 16 weeks of
gestation for all except K which can be undertaken from 20 weeks, due to the risk of a false negative
result if performed earlier in pregnancy.