Introduction and background Essential thrombocythaemia (ET) is a myeloproliferative disorder of unknown aetiology characterised by an abnormal increase in platelet count. As 20% of patients may be younger than 40 years of age the association of ET and pregnancy may not be rare. Pregnancy complications may be spontaneous miscarriage, premature delivery, stillbirth, and intrauterine growth retardation, preeclampsia, abruptio placentae and thromboembolism. Cytoreductive agents and anagrelide are not currently recommended for use in pregnancy due to risk of teratogenecity. Interferon is considered the agent of choice in pregnancy with ET with low-dose aspirin to enhance pregnancy outcome.

Case summary A 34 year old woman with JAK2 negative ET was seen by haematologist at 7 weeks gestation when her platelet count was 995x106. She was para 2, BMI of 33. She was on anagrelide which was stopped immediately. She was started on Alpha interferon and low dose aspirin. At 28 weeks her platelet count increased. Interferon dose was doubled. An ultrasound scan at 34 weeks showed normal foetal growth. Apart from complaints of headache and myalgia, the pregnancy was uneventful until 35 weeks when she started spontaneous labour and gave birth to a premature male baby of 2.1kg. Postpartum she had Clexane for 7 days and was started on Anagrelide with interferon and aspirin.

Conclusion Available data have not shown association of interferon with a higher incidence of foetal malformation in humans. In ET careful multidisciplinary management involving obstetricians, haematologist and paediatricians can bring about good pregnancy outcome.