Immune Thrombocytopenia in Pregnancy

Immune thrombocytopenia in pregnancy is isolated autoimmune destruction of platelets, with a count below 100 x 10^9/L and no other cause, in a pregnant woman. It may be known before pregnancy or first appear in it. Maternal antibodies cross the placenta, so some babies have low platelets, and the count near delivery decides safe analgesia and birth.

• Associated conditions: HIV, hepatitis C, systemic lupus erythematosus, antiphospholipid syndrome, thyroid disease.
• Serious maternal bleeding is uncommon above 20 x 10^9/L.
• Some babies have low platelets at birth.

Women have easy bruising, petechiae, nosebleeds, gum bleeding or heavy menstrual bleeding, or no symptoms. Blood pressure is normal and the spleen is not enlarged.

• Petechiae and purpura usually appear below 30 x 10^9/L.
• Normal liver enzymes and clotting.
• Differential diagnosis: gestational thrombocytopenia, preeclampsia and HELLP syndrome, HIV, malaria, thrombotic thrombocytopenic purpura, antiphospholipid syndrome, systemic lupus erythematosus, drug induced thrombocytopenia, hypersplenism.
• Complications: haemorrhage, postpartum haemorrhage, intracranial bleeding, spinal haematoma after neuraxial block, neonatal thrombocytopenia, treatment side effects.

The diagnosis is by exclusion, with a repeat count and a film showing no fragments or clumps.

• Full blood count and film; liver enzymes, lactate dehydrogenase, creatinine, coagulation screen, blood pressure and urine protein.
• HIV, hepatitis B and C tests, malaria test, antinuclear antibody, antiphospholipid antibodies, vitamin B12, folate, TSH.
• A count below 100 x 10^9/L before 20 weeks, or a known earlier low count, supports the diagnosis.
• Bone marrow examination only if other cytopenias or atypical features are present.

The principle is to treat only when the count is low enough to risk bleeding or delivery, using the lowest effective steroid dose.

• Supportive: avoid IM injections, aspirin and NSAIDs when platelets are below 50 x 10^9/L; avoid contact activities; deliver in a facility with blood bank; check glucose and blood pressure on steroids.
• Pharmacological: no treatment if platelets are 30 x 10^9/L or above and there is no bleeding; prednisolone 0.5 to 1 mg/kg oral daily (maximum 60 mg) for platelets below 30 x 10^9/L, bleeding, or before delivery, continued until the count rises then tapered over 2 to 4 weeks; immunoglobulin 1 g/kg IV daily for 1 to 2 days for platelets below 20 x 10^9/L with bleeding, or for rapid rise before delivery; methylprednisolone 1 g IV daily for 3 days with immunoglobulin for life-threatening bleeding; azathioprine 2 mg/kg oral daily (maximum 150 mg) as a steroid sparing drug; calcium carbonate 1 g oral daily with prednisolone; tranexamic acid 1 g IV over 10 minutes for postpartum bleeding, repeated once after 30 minutes if bleeding continues.
• Procedures: platelet transfusion of one adult dose for platelets below 50 x 10^9/L at caesarean section or with active bleeding, and below 30 x 10^9/L for vaginal birth; epidural or spinal block if platelets are 70 x 10^9/L or above and stable; avoid vacuum extraction, rotational forceps, scalp electrodes and fetal scalp sampling.
• Special groups: the newborn has a cord platelet count and repeat counts on days 2 to 5, and receives immunoglobulin 1 g/kg IV for platelets below 30 x 10^9/L with bleeding or below 20 x 10^9/L; avoid mycophenolate and cyclophosphamide.
• Red flags: platelets below 30 x 10^9/L, mucosal bleeding, severe headache, blood pressure above 140/90 mmHg, jaundice, fever.
• Follow-up: platelet count every 2 to 4 weeks, weekly from 36 weeks and at admission in labour; repeat at 6 weeks postpartum; contraception advice.