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Chapter 11

OBSTETRICS

PRACTICE POINTS

  • Anaemia is common in pregnancy due to increased plasma volume, co-morbidities and nutrition.
  • Prophylactic iron and folate during pregnancy is indicated.
  • The decision to transfuse blood should not be based on haemoglobin levels alone, but also on the patient’s clinical need.
  • Obstetric bleeding may be unpredictable and massive. Every obstetric unit should have a current protocol for major obstetric haemorrhage.
  • If disseminated intravascular coagulation is suspected, do not delay treatment while waiting for the results of coagulation tests.
  • The administration of Anti-D immunoglobulin to all RhD negative mothers within 72 hours of delivery or any sensitising event during pregnancy (e.g. miscarriage, antenatal haemorrhage, invasive procedure) is the preferred approach to the prevention of Rh disease of the newborn.

Refer to the national obstetric guidelines.

11.1 INTRODUCTION

During pregnancy the physiology and metabolism of the female changes to accommodate the fetus and placenta. A number of key aspects are of importance:

  • Anaemia in pregnancy is a haemoglobin concentration of less than 11 g/dL in the first and third trimesters and 10.5 g/dL in the second trimester.
  • The diagnosis and effective treatment of chronic anaemia in pregnancy is an important way of reducing the need for future transfusions. The decision to transfuse blood should not be based on haemoglobin levels alone, but also on the patient’s clinical need.
  • Blood loss during normal vaginal delivery or Caesarean section does not normally necessitate transfusion provided that the maternal haemoglobin is above 10.0–11.0 g/dL before delivery.
  • Obstetric bleeding may be unpredictable and massive. Every obstetric unit should have a current protocol for major obstetric haemorrhage and all staff should be trained to follow it.
  • If disseminated intravascular coagulation is suspected, do not delay treatment while waiting for the results of coagulation tests.
  • The administration of Anti-RhD immunoglobulin to all RhD negative mothers within 72 hours of delivery or any sensitising event during pregnancy (e.g. miscarriage, antenatal haemorrhage, invasive procedure) is the preferred approach to the prevention of Rh disease of the newborn.

11.2 HAEMATOLOGICAL CHANGES IN PREGNANCY

The following haematological changes occur during pregnancy:

  • 40–50% increase in plasma volume, reaching its maximum by week 32 of gestation, with similar increase in cardiac output.
  • Increase in red cell volume is modest, 0–25%, though more slowly than the increase in plasma volume.
  • Normal or elevated haemoglobin may signify pre-eclampsia in which plasma volume is reduced.
  • Increased iron requirement, particularly in last trimester.
  • Increases in platelet activation and levels of coagulation factors, particularly fibrinogen, Factor VIII and Factor IX.
  • Fibrinolytic system is suppressed.
  • Increased susceptibility to thromboembolism.

11.2.1 Blood loss during delivery (normal)

  • About 200 mL of blood during normal vaginal delivery.
  • Up to 500 mL during caesarean section.

This blood loss rarely necessitates transfusion provided that the maternal haemoglobin is above 10.0–11.0 g/dL before delivery. Further investigation is needed if haemoglobin concentration does not return to normal by 8 weeks postpartum.

11.2.2 Prevention of anaemia in pregnancy

The need for transfusion can often be avoided by the prevention of anaemia through:

  • education about nutrition, food preparation and breastfeeding,
  • adequate maternal and child health care,
  • access to family planning information, education and services,
  • clean water supplies, and
  • adequate facilities for the disposal of human waste.

Prophylactic administration of iron and folic acid is strongly indicated during pregnancy in countries where iron and folate deficiency is common. 

Examples of the dose regime are:
  • Optimum daily doses to prevent nutritional anaemia in pregnant women:
    - 120 mg elemental iron, and
    - 1 mg folate.

  • When anaemia is already present, especially if severe, higher daily therapeutic doses may be more effective:
    - 180 mg elemental iron, and
    - 2 mg folate.

11.3 TRANSFUSION

The decision to transfuse blood should not be based on haemoglobin levels alone, but also on the patient’s clinical need. The following factors must be taken into account:

  • stage of pregnancy,
  • evidence of cardiac failure,
  • presence of infection: e.g. pneumonia, malaria,
  • obstetric history,
  • anticipated delivery, vaginal or caesarean section, and
  • haemoglobin level.

11.3.1 Major obstetric haemorrhage

Acute blood loss is one of the main causes of maternal mortality. It may be a result of excessive bleeding from the placental site, trauma to the genital tract and adjacent structures, or both. Increasing parity increases the incidence of obstetric haemorrhage.

Serious haemorrhage may occur at any time throughout pregnancy and the puerperium.

Major obstetric haemorrhage can be defined as any blood loss occurring in the peripartum period, revealed or concealed, that is likely to endanger life.

At term, blood flow to the placenta is approximately 700 mL per minute.

The patient’s entire blood volume can be lost in 5–10 minutes. Unless the myometrium contracts on the placental site appropriately, rapid blood loss will continue, even after the third stage of labour is complete.

  • Obstetric bleeding may be unpredictable and massive.
  • Major obstetric haemorrhage may result in clear signs of hypovolaemic shock but because of the physiological changes induced by pregnancy, there may be few signs of hypovolaemia, despite considerable blood loss.

Signs of hypovolaemia include:

  • Tachypnoea,
  • thirst,
  • Hypotension,
  • Tachycardia,
  • increased capillary refill time,
  • reduced urine output, and
  • decreased conscious level.

It is therefore essential to monitor and investigate a patient with an obstetric haemorrhage, even in the absence of signs of hypovolaemic shock. Be ready and prepared to resuscitate, if necessary.

11.4 RhD NEGATIVE PREGNANCY

A person has the RhD negative phenotype when the RHD gene is the absent. Homozygosity or heterozygosity for RHD will lead to a RhD positive phenotype. The majority of the Cambodian population is RhD positive.

An RhD negative pregnant woman is at risk of developing anti-D if her fetus is RhD positive. Generally the first pregnancy sensitises the woman and subsequent exposure will cause anti-D production. Circulating anti-D can cross the placenta and cause significant in-utero anaemia and hyperbilirubinaemia called Haemolytic Disease of the Newborn (HDN).

HDN can be prevented by the prevention of anti-D antibody formation in women with child-bearing potential (pre-adolescent or menstruating females):

  • Only transfuse RhD negative erythrocytes to RhD negative females of child-bearing potential.
  • If a female of child-bearing potential is exposed to RhD (e.g. RhD positive platelet transfusion), offer adequate Anti-D within 72 hours to haemolyse any transfused red cells.
  • Offer prophylactic Anti-D injections to all pregnant RhD negative women and aAnti-D for any pregnancy event which may be complicated by fetomaternal haemorrhage.

Note: Once a patient has developed anti-D, administration of prophylactic Anti-D is not effective.

Anti-D is an intramuscular preparation (IM) and is used for prophylaxis against sensitising events and for routine prophylaxis. Intravenous Anti-D is available and should be considered when larger doses are required. 

11.4.1 Routine Anti-D prophylaxis

Prophylaxis is indicated for RhD negative women who have not already made anti-D. Either:

  • at least 500 IU given IM at 28 and 34 weeks, or
  • at least 1250 IU given IM at 28 weeks.

These doses should be given irrespective of previous doses of Anti-D.

11.4.2 Anti-D event prophylaxis

Prophylaxis is indicated for the following potentially sensitising events in RhD negative women who have not already made anti-D:

Before 12 weeks (First trimester):

  • Uncomplicated spontaneous miscarriage without pain has a low risk of sensitising the woman and Anti-D is not required.
  • Any other event involving pain, bleeding, instrumentation (including amniocentesis), ectopic pregnancy or termination of pregnancy requires a dose of at least 250 IU given IM.

After 12 weeks:

  • For any event which may involve fetomaternal haemorrhage, administer at least 500 IU Anti-D given IM.

Potentially sensitising events are:

  • abdominal trauma,
  • antepartum haemorrhage, both revealed and concealed,
  • external cephalic version,
  • miscarriage or termination of pregnancy,
  • intrauterine death,
  • ectopic pregnancy,
  • intervention with a sampling device e.g. chorionic villus sampling, and
  • delivery.

A standard dose of at least 500 IU given IM is required. If Kleihauer testing is available, estimate the size of the fetomaternal haemorrhage and the dose of Anti-D can be increased. Approximately 100–125 IU Anti-D is required for every 1 mL fetal red cells (0.5 mL fetal whole blood) involved in the fetomaternal haemorrhage.

All Anti-D is administered IM. Some preparations can be administered IV and this can be useful if very large doses are required.

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