Low molecular weight heparin to prevent recurrent venous thromboembolism in pregnancy: a randomised trial of two doses: the HIGHLOW study

Women who are pregnant have an increased chance of developing blood clots. These clots can cause serious ill-health and can even be fatal. The death of a young mother is a tragic event with wide-reaching effects on the woman's family.

Women with a previous blood clot have a higher recurrence risk in pregnancy. In fact, the risk is so high that clot-preventing medication is warranted during the entire pregnancy and for 6 weeks after delivery. However, although the stakes are so high, we simply do not know what the correct medication dose is for these patients because this critically important question has not been answered in the past by a good study.

In this study, "HIGHLOW", doctors in Ireland and in other countries will join together to perform a large study comparing the two doses of clot-preventing medication recommended by guidelines for pregnant women who have had a previously diagnosed blood clot. We will determine which dose is most effective (in terms of preventing a new blood clot) and safest (in terms of side-effects such as bleeding).

We have been tremendously successful in a pilot Irish site. We now request funding to scale this up to include 6 Irish sites. In total, we estimate that Ireland will contribute a third of all patients to this international study.

This type of research is sadly lacking in pregnant women. As a consequence, doctors make decisions on the health of some of their highest risk pregnant patients using evidence that is of poor quality or that is extrapolated from patients that are not pregnant.

In Ireland, a staggering 160 patients experienced pregnancy-associated blood clots in 2012. Therefore, it is of great national and international importance that this study is supported for the benefit of our pregnant mothers and their familes.


Award Date
24 February 2017
Award Value
Principal Investigator
Professor Fionnuala Ni Ainle
Host Institution
Royal College of Surgeons in Ireland
DIFA 2017