Background: Inherited antithrombin deficiency is a rare, high-risk thrombophilia associated with obstetric and neonatal morbidity and mortality. The use of low molecular weight heparin (LMWH) and antithrombin concentrate (AT3) appears to improve maternal and fetal outcomes; however, there is a lack evidence-based recommendations to guide clinicians in the management of these complex pregnancies.

Aims: To provide a descriptive analysis of the management of all pregnancies (>20 weeks gestation) in women with inherited antithrombin deficiency across Western Australia from January 2015 – January 2022.

Methods: We undertook a multicentre, retrospective cohort analysis based on predefined maternal characteristics, LMWH dosing (weight-based vs anti-Xa guided), AT3 use and maternal and neonatal outcomes.

Results: Seven women with inherited antithrombin deficiency delivered eight live infants. The average maternal age was 33 years and 50% of pregnancies were conceived on LMWH. LMWH was initially weight-based (1mg/kg BD) then up-titrated to achieve an anti-Xa level between 0.6-1.0 IU/mL. The average dose of LMWH was 1.39mg/kg BD, however wide variation in LMWH dosing was noted (1.03-1.90mg/kg BD). Two women required non-elective caesarean sections for obstetric indications, but all deliveries received AT3 at induction followed by an additional dose 24 hours later. There was marked variation in dosing (amount and duration) of AT3 based on clinicians’ prescribing preferences and clinical need. One woman had a large volume postpartum haemorrhage, two women developed wound haematomas and one woman developed a sagittal sinus thrombosis on day 19 postpartum. Four pregnancies were affected by significant placental insufficiency including severe preeclampsia and intrauterine growth restriction. Two neonates required admission to Neonatal Intensive Care.

Conclusion(s): The Western Australian experience of inherited antithrombin deficiency in pregnancy mirrors international literature, with significant maternal and fetal morbidity despite variable use of LMWH and AT3. There is a need for development of evidence-based guidelines to improve outcomes in these high-risk pregnancies.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/management-of-inherited-antithrombin-deficiency-in-pregnancy-the-western-australian-experience/