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OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Anaemia and thrombocytopenia in pregnancy

Obstetrics and gynaecology · UK scope · Sources checked 7 Sept 2026 · Clinical review pending

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Cytopenia with bleeding or organ dysfunction

Anaemia or thrombocytopenia accompanied by haemodynamic instability, active bleeding, hypertension, upper abdominal pain, neurological signs or haemolysis may indicate haemorrhage, HELLP or thrombotic microangiopathy.

Action: Arrange urgent maternity and haematology assessment, assess circulation and bleeding, repeat the blood count with film, and request renal, liver, haemolysis and coagulation studies while treating the suspected emergency.

Overview

Distinguish physiological blood-count changes from iron deficiency, immune thrombocytopenia and obstetric emergencies, and plan investigation, treatment and delivery-related safety.

Antenatal full blood counts provide an opportunity to detect a treatable reduction in maternal reserve before birth. Anaemia increases fatigue and can make a subsequent haemorrhage less well tolerated, but the investigation should identify why haemoglobin is low rather than treating all results alike. Review previous counts, gestation, diet, bleeding, gastrointestinal symptoms, ethnicity and haemoglobinopathy status, medications and inflammatory or renal disease. Microcytosis supports iron deficiency or a haemoglobinopathy; a normal mean cell volume does not exclude iron depletion, especially with mixed deficiencies.

Iron deficiency is common because maternal erythropoiesis and fetal requirements increase demand on finite stores. Ferritin is useful but is also an acute-phase reactant. A low result is persuasive, whereas a normal result in inflammatory illness needs interpretation alongside the clinical picture. A response to oral iron can support the working diagnosis, provided the patient actually receives and tolerates it. If haemoglobin does not rise as expected, first establish adherence, dose and administration, then investigate ongoing blood loss, impaired absorption or another cause instead of automatically escalating the dose.

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Obstetrics and gynaecologyOriginal SBA

A tolerable elemental iron regimen

At 26 weeks, a stable patient has haemoglobin 99 g/L and ferritin 12 micrograms/L. Which initial regimen and review best matches current UK BSH advice?

Choose one answer, then submit
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Sources and review status5 sources · checked 7 Sept 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 7 Sept 2026; clinical approval remains outstanding.

  • BSH UK iron deficiency in pregnancy guideline
  • BSH iron deficiency pregnancy guideline landing page
  • NHS Greater Glasgow thrombocytopenia in pregnancy
  • NICE NG133 hypertensive pregnancy disease
  • NICE NG201 antenatal screening recommendations

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom

Thrombocytopenia has a different diagnostic logic. Mild isolated reduction arising late in pregnancy commonly reflects gestational thrombocytopenia, particularly when counts were normal before and early in pregnancy and there is no bleeding. Earlier onset, lower counts or a prior history makes immune thrombocytopenia more likely. Hypertension, proteinuria, liver abnormalities or haemolysis points towards pregnancy microangiopathy; neurological symptoms and disproportionate renal injury broaden that concern. Platelet clumping in an EDTA sample can produce a spurious result and should be checked with the laboratory.

Birth planning brings the two problems together. Optimise haemoglobin before delivery when possible, document the likely cause of low platelets, and obtain anaesthetic advice early enough to discuss analgesia and operative options. No universal platelet number guarantees neuraxial safety because trend, cause, coagulation, medication and bleeding phenotype matter. Active haemorrhage is managed by a major obstetric haemorrhage pathway; stable iron deficiency usually needs haematinic replacement rather than transfusion. Decisions about transfusion use symptoms, bleeding, haemoglobin and the time available for recovery.

Key points

  • Pregnancy expands plasma volume more than red-cell mass, but haemodilution must not be assumed to explain every low haemoglobin.
  • UK BSH thresholds define anaemia as haemoglobin below 110 g/L in the first trimester, below 105 g/L in later pregnancy and below 100 g/L postpartum.
  • Ferritin below 30 micrograms/L supports iron deficiency; inflammation can conceal depleted stores behind a normal or elevated result.
  • Treat established iron deficiency with a tolerable oral elemental iron dose and check the haemoglobin response after about two to three weeks.
  • Gestational thrombocytopenia is usually mild, isolated and late, with no bleeding or systemic illness and postpartum resolution.
  • Platelet timing, trend, film and accompanying features determine the differential and urgency more reliably than a single number.

Aetiology

01

Reduced haemoglobin

Iron depletion, haemoglobinopathy, B12 or folate deficiency, inflammation, renal disease and blood loss can coexist with physiological dilution and require different treatment strategies.

02

Reduced platelets

Gestational thrombocytopenia and immune destruction are common considerations, while pre-eclampsia-associated consumption, other microangiopathies, drugs and laboratory artefact require active exclusion when features suggest them.

Pathophysiology

  1. 1
    Dilution and demand

    Plasma expansion exceeds the increase in erythrocyte mass, while pregnancy increases iron requirements; inadequate stores convert physiological dilution into clinically significant deficiency.

  2. 2
    Platelet turnover

    Pregnancy-associated haemodilution and increased platelet turnover can modestly reduce counts without pathological bleeding, usually with late onset and recovery following birth.

  3. 3
    Immune or consumptive loss

    Antibody-mediated platelet destruction differs from microvascular consumption and clotting activation; the accompanying blood film, organ function and clinical pattern help distinguish these mechanisms.

Clinical features and red flags

Iron-depletion symptoms

Fatigue, exertional breathlessness, palpitations or pica warrant blood-count and iron-store assessment, although symptoms overlap with normal pregnancy and other disease.

Haemoglobinopathy possibility

Long-standing microcytosis, family history or an abnormal screening result requires condition-specific interpretation before repeated iron is prescribed without evidence of deficiency.

Likely gestational thrombocytopenia

Late mild isolated thrombocytopenia with a normal early count, no bleeding and no systemic abnormalities supports a benign pregnancy-associated process.

Immune or systemic disease

Earlier thrombocytopenia, marked bruising, mucosal bleeding, falling counts or associated renal, hepatic and neurological findings makes simple gestational change less convincing.

Red flags requiring action

  • Bleeding with cardiovascular compromise, chest pain, syncope or severe breathlessness requires emergency assessment rather than an outpatient iron prescription.
  • A rapidly falling platelet count with hypertension, epigastric pain, renal impairment or neurological symptoms requires urgent exclusion of HELLP and thrombotic microangiopathy.
  • Very low platelets, spontaneous mucosal bleeding or a new additional cytopenia needs prompt haematology involvement regardless of gestation.

Investigations

  1. 01
    Full blood count with prior-result comparisonFirst step
    Why
    Characterise haemoglobin, indices, platelets and whether more than one cell line is affected.
    Interpretation and limitations
    Interpret against gestation and trend; rapidly changing values or combined abnormalities deserve faster assessment than stable isolated mild changes.
  2. 02
    Ferritin and selected haematinics
    Why
    Identify iron depletion and investigate B12 or folate deficiency when history or indices support it.
    Interpretation and limitations
    Ferritin below 30 micrograms/L supports iron deficiency, while inflammatory states and mixed deficiencies can make a single apparently normal result misleading.
  3. 03
    Blood film and repeat platelet sample
    Why
    Check morphology, haemolysis and whether the low platelet count is an analytical artefact.
    Interpretation and limitations
    Platelet clumping suggests pseudothrombocytopenia and can require a different collection tube; red-cell fragments require urgent assessment for microangiopathic disease.
  4. 04
    Blood pressure, proteinuria, renal and liver tests
    Why
    Look for a pregnancy hypertensive or multisystem explanation for low platelets.
    Interpretation and limitations
    Proteinuria, rising creatinine or liver injury changes urgency; absence of major hypertension does not rule out HELLP when other features fit.

Differential diagnosis

01

Iron deficiency versus inherited microcytosis

Low ferritin supports iron depletion, while disproportionate longstanding microcytosis or a haemoglobinopathy screen suggests inherited disease; both can occur in the same patient.

02

Gestational versus immune thrombocytopenia

Earlier onset, lower values, previous thrombocytopenia or bleeding favours an immune process; late mild isolated reduction with recovery supports gestational thrombocytopenia.

03

HELLP and thrombotic microangiopathy

Haemolysis with platelet decline and liver, kidney or neurological abnormalities requires urgent specialist assessment because delivery alone may not treat every microangiopathic disorder.

Management

01Iron replacementTreat confirmed or strongly suspected iron deficiencyFirst stepAnaemia and clinical or laboratory findings support depleted iron stores without immediate instability.+
  1. 1Offer 40–80 mg elemental oral iron daily using a preparation and schedule the patient can tolerate, with explanation of gastrointestinal effects.
  2. 2Separate iron from interacting medicines and foods where practical, and arrange a haemoglobin check after roughly two to three weeks.
  3. 3If response is poor, assess adherence and cause; consider specialist intravenous iron after the first trimester when oral treatment is ineffective, intolerable or too slow.
02Platelet assessmentIdentify the cause before birth approachesA low platelet count is found during antenatal screening or assessment.+
  1. 1Confirm the result with film and prior counts, ask about bleeding and medicines, and examine for hypertension or another systemic disorder.

Complications

01

Reduced haemorrhage reserve

Anaemia reduces the ability to tolerate obstetric blood loss and may increase symptoms, transfusion requirements and difficulty recovering during the postnatal period.

02

Bleeding and procedural constraints

Significant thrombocytopenia or coagulopathy can increase bleeding and alter anaesthetic choices, requiring planned communication rather than a last-minute decision during labour.

03

Missed underlying disorder

Attributing abnormal counts to normal pregnancy can delay recognition of haemoglobinopathy, nutritional disease, immune thrombocytopenia or a rapidly progressive multisystem emergency.

Monitoring and follow-up

  • Record the planned early haemoglobin response check and actively follow up a missed sample or lack of improvement.
  • Continue replacement long enough to rebuild stores, reviewing postpartum blood loss and symptoms rather than stopping tablets as soon as haemoglobin rises.
  • For thrombocytopenia, schedule counts according to level, gestation and trend, and arrange earlier review for bruising or mucosal bleeding.
  • Confirm postpartum platelet recovery when gestational thrombocytopenia is suspected; persistence changes the diagnosis and requires haematology follow-up.

Special situations

Ferritin needs context

Inflammation can increase ferritin despite depleted accessible iron, so a reassuring-looking number should not override a coherent history and other laboratory evidence.

Iron amount versus tablet strength

A 200 mg ferrous sulfate tablet contains far less than 200 mg elemental iron; prescriptions and comparisons must make the distinction explicit.

Immune thrombocytopenia and the baby

Maternal platelet antibodies can affect neonatal platelets, whereas uncomplicated gestational thrombocytopenia does not carry the same immune mechanism or neonatal plan.

Transfusion is a clinical decision

Stable anaemia without bleeding is usually corrected with replacement therapy; transfusion decisions require symptoms, haemodynamic status, comorbidity and time before anticipated birth.

Common pitfalls

  1. 01

    Calling every antenatal low haemoglobin physiological without reviewing the threshold, trend and iron stores.

  2. 02

    Increasing iron repeatedly without asking whether nausea or constipation prevents the patient from taking it.

  3. 03

    Accepting an isolated automated low platelet result without considering sample clumping or reviewing a blood film.

  4. 04

    Assuming a late-pregnancy platelet fall is benign despite hypertension, epigastric pain, haemolysis or renal impairment.

05
Reticulocytes, LDH, haptoglobin and coagulation selectively
Why
Investigate haemolysis, marrow response or bleeding-related consumption when clinically indicated.
Interpretation and limitations
Results must be interpreted together, because anaemia from iron deficiency alone should not cause schistocytes, profound platelet decline or coagulopathy.
  • 2Arrange obstetric haematology review for early, marked, progressive or symptomatic thrombocytopenia, or uncertainty about its cause.
  • 3Coordinate repeat counts, treatment if immune thrombocytopenia is significant, and an individual anaesthetic and delivery plan before labour.
    • 03Urgent cytopeniaEscalate bleeding or microangiopathic featuresEscalationBlood-count abnormalities occur with clinical deterioration, haemorrhage or signs of organ injury.+
    1. 1Activate emergency obstetric care and resuscitation when bleeding or instability is present, including rapid access to blood-component support.
    2. 2Obtain urgent haemolysis, renal, hepatic and coagulation results and involve haematology for HELLP, TTP or other consumptive disease.
    3. 3Treat the underlying emergency and reassess counts after delivery; persistent thrombocytopenia requires ongoing investigation rather than retrospective labelling as gestational.
    Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
    A practical UK oral regimen within the BSH 40–80 mg elemental iron daily range.

    Ferrous sulfate

    One ferrous sulfate 200 mg tablet orally once daily provides approximately 65 mg elemental iron; review response after two to three weeks and continue replacement for three months after haemoglobin normalises and at least six weeks postpartum.

    Explain nausea, constipation and dark stools; separate from levothyroxine and other interacting drugs, and keep securely away from children.

    Replaces iron when oral therapy fails, cannot be tolerated or cannot act quickly enough before birth.

    Intravenous iron

    After the first trimester, calculate replacement from body weight, haemoglobin deficit and the chosen product’s maximum single and weekly doses; administer in a monitored service with resuscitation facilities.

    Confirm deficiency first; infusion reactions and product-specific hypophosphataemia risk require counselling, and active infection or alternative anaemia may alter suitability.