Incidence and management of 82 cases of pregnancy‐associated venous thromboembolism occurring at a single centre – Response to Lyall & Myers (2008)

We were interested to read Lyall and Myers’ retrospective report from a single centre and, like the authors, were struck by the similarity of the data. This increases our confidence that we obtained an accurate snapshot of current practice in the UK (Voke et al, 2007). Several points are worth highlighting. The Nottingham study estimated combined incidence of antenatal and postpartum events of 1.01 per 1000 births is in line with other published studies. Our study (Voke et al, 2007) did not attempt to estimate the incidence of antenatal venous thromboembolism (VTE) in the 25 participating centres as we could not guarantee identification of 100% of cases in every hospital participating. Our objective was to collect data from as many centres as possible to give a wide view of the varied antenatal VTE management in the UK and Ireland. Lyall & Myers included cerebral vein thrombosis which is a serious complication of pregnancy [Confidential Enquiry into Maternal and Child Health (CEMACH, 2007)] and should be included in reports of antenatal thrombotic events. However our survey focused on deep vein thrombosis in the legs and pulmonary embolism and excluded postpartum VTE. We particularly studied the varied & unvalidated antenatal management of VTE in the UK rather than postpartum treatment, which uses the well-established regimens used in the non-pregnant patient. The optimal low molecular weight heparin (LMWH) dosing regimen in pregnancy has not been clearly established. Collectively, the two studies showed wide variability in treatment schedules between and within centres, without any evidence for superiority of one regime over another. The practice of dose reduction also varied widely. In selected Nottingham patients, the conversion to once daily dose as pregnancy advanced appeared to be safe and effective, as it was in the 22% of mothers who received this treatment in our study. Once daily injections (as used in non-pregnant patients and given to a minority of the Nottingham antenatal patients and to 66% in our study) appears to be a safe and popular option for women with calf deep vein thrombosis or those in whom there has been clinical resolution of symptoms after several weeks of twice daily injections. These findings raise the possibility that this more convenient regimen could have wider application in the treatment of VTE in pregnancy. However this needs to be tested in an appropriately powered randomised case controlled study. The noted risk factors emphasised the importance of thrombophilia, family history and previous venous thromboembolic disease. The relatively low number of patients on thromboprophylaxis in both surveys suggest a failure of effective antenatal screening and appropriate referral. Both studies noted that a proportion of women who failed thromboprophylaxis were on low doses. This provides some validation of the dosing regimen currently recommended by the Royal College of Obstetricians and Gynaecologists (RCOG 2004). Our study found poor documentation of dose and timing of peripartum anticoagulation. This was better in Lyall & Myers’ study, perhaps reflecting more consistent record keeping in a single centre. The implication is that improvements in record keeping are needed and can be achieved, to ensure safe delivery and reduce the risk of early postpartum haemorrhage. Full anticoagulation within the first few days, particularly with early transfer to warfarin, increased the risk of postpartum haemorrhage in both studies, suggesting that transfer to warfarin should be delayed for 1–4 weeks. In the absence of large case controlled or comparative antenatal studies, surveys, such as ours (Voke et al, 2007) and that of Lyall & Myers, provide a valuable contribution to our understanding of risk factors and management of VTE in pregnancy.