By Dr Jasmine Ramiah — Clinical Haematology
Introduction:
The clinical state of pregnancy drives profound haematological adaptation to support the developing foetus and prepare for post-delivery. In South Africa, maternal mortality remains approximately 100-110 deaths per 100 000 live births with many deaths related to preventable haematological and medical conditions. As a clinician understanding the delicate balance between states of physiology and pathology is essential in ensuring effective antenatal support.
This overview aims to highlight anaemia, thrombocytopenia, and venous thromboembolism (VTE) risk, with practical thresholds for investigation and referral.
Physiologic changes in pregnancy
The maternal plasma volume expands by approximately 40–50% from early gestation resulting in a physiological increase in the red cell mass of approximately 20-40%.
These anticipated physiological changes result in a decrease in haemoglobin (Hb) typically most marked in the second trimester owing to the effects of haemodilution. In addition a mild leukocytosis is common, while platelet counts may trend slightly downward owing to a physiological stated of increased consumption and dilution. Coagulation shifts toward a prothrombotic state in order to mitigate the added risk of haemorrhage postpartum.
Anaemia in pregnancy
Iron deficiency anaemia (IDA) is the most common cause of anaemia in pregnancy
This may be owing to the increased physiological demand as the iron requirements rise substantially (≈1g total across pregnancy and postpartum) driven by maternal erythropoiesis, the demands of the growing foetus and placenta.
In order to identify IDA, a full blood count (FBC) at booking and at 24–28 weeks is recommended for screening and diagnosis.
The World Health Organisation (WHO) has defined anaemia in pregnancy based on the gestational age: Hb <11 g/dL (1st trimester), <10.5 g/dL (2nd), <11 g/dL (3rd).
Iron deficiency can be confirmed with serum iron studies with a focus on a low ferritin (<30 µg/L is suggestive; <15 µg/L diagnostic), microcytosis on peripheral blood smear, and low transferrin saturation. These parameters must always be interpreted in the clinical context in conjunction with a dietary and family history, pregnancy and breastfeeding history. One may manage iron deficiency in pregnancy with oral supplementation. The indications for intravenous formulations include intolerance to oral therapy, a poor clinical and biochemical response (after 2-4 weeks of ensured adherence), late gestation and malabsorption states.
Thrombocytopenia: benign vs concerning
Platelet counts normally decline slightly as the pregnancy progresses owing to the haemodilution effect. Gestational thrombocytopenia (GT) accounts for approximately 75% of cases.
Gestational thrombocytopenia typical occurs as a late onset in the 2nd and 3rd trimester with a mild t thrombocytopenia of between 100-15 ×10⁹/L), late onset (2nd–3rd trimester). These patients are often asymptomatic with no significant contributory history. Observation is the recommended management until the platelet count resolves postpartum.
More sinister pathologies include immune thrombocytopenia (ITP). The platelet count is often severely low (<100 x 109/L) resulting in mucocutaneous bleeding. This condition requires intervention with oral or intravenous steroids, dosed depending on the weight if the platelet count is <30 ×10⁹/L or bleeding. Closer to the time of deliver the patient may require intravenous immunoglobulin to rapidly increase the platelet count for a safe deliver (≥50 for vaginal, ≥80–100 for neuraxial anaesthesia).
HELLP syndrome (Haemolysis, Elevated Liver enzymes, Low Platelets) is a life threatening emergency presenting with clinical hypertension/proteinuria and a moderate to severe thrombocytopenia often <100 ×10⁹/L with haemolysis and transaminitis. This obstetric emergency requires stabilisation expediting the delivery.
Venous thromboembolism (VTE) risk
The physiological state of pregnancy and postpartum (the puerperium) confer a 4–5 times increased VTE risk. The risk factors include prior VTE, thrombophilia, obesity, immobility, caesarean delivery, preeclampsia, multiparous, age >35 and smoking history. The management starts with prevention and early identification of the risk factors, institution of weight adjusted low molecular weight heparin (LMWH) for prophylaxis in high-risk individuals. One should be mindful of the clinical presentation of VTE such as unilateral leg pain or swelling, chest pain and shortness of breath or a subtle increase in heart rate (tachycardia) and the urgent necessity for investigational confirmatory imaging such as compression ultrasound for deep vein thrombosis (DVT); V/Q scan or CTPA for pulmonary embolus (PE) and therapeutic anticoagulation with LMWH. Do not hesitate to investigate and treat.
Conclusion
Clear recognition of normal physiological shifts is paramount paired with timely appropriate investigations of the red flags allows for protection of both the mother and baby because in pregnancy blood changes are expected but missing the warning signs isn’t.
Safe maternal care is structured by the backbone of screening: early iron optimisation, careful evaluation of thrombocytopenia, and vigilant VTE risk management. Maternal care is not the blood parameter numbers alone but knowing when they matter.