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Pregnancy outcomes in women with artificial heart valves

Key points

  • Lifelong anticoagulation is required to prevent thrombosis in women with artificial heart valves.
  • Warfarin, the usual anticoagulant, can cause fetal abnormalities. Low molecular weight heparin (LMWH) injections can be used instead and these are safe for the baby, but concerns have been expressed about their efficacy in protecting the mother against heart valve thrombosis.
  • This study will provide population-based information about the risks associated with an artificial heart valve in pregnancy and the different anticoagulation regimes in order to inform future management guidance.

Surveillance Period

1stFebruary 2013 – 31st January 2015


Women with mechanical prosthetic heart valves require lifelong anticoagulation, usually with warfarin, to prevent valve thrombosis. During pregnancy their thrombotic risk increases (estimated to be as high as 29%[1] with a 2.9% maternal mortality rate[2]). Thus, the need for effective anticoagulation is greater. Warfarin treatment throughout pregnancy appears to have the lowest risk of maternal thrombotic complications[2] but is associated with a higher fetal loss rate (estimates as high as 59%)1and can have damaging effects on the fetus[2]. In contrast, unfractionated heparin or low molecular weight heparin are safe for the fetus, but doubts have been expressed about their efficacy in preventing maternal thrombotic complications[3]. Factors, such as the type and position of the mechanical valve, choice of anticoagulant regime and patient compliance may all affect the rate of thrombosis.

Counselling of women with artificial heart valves about the risks during pregnancy is difficult due to the paucity of good data relating to maternal or fetal outcomes. Recommendations from various expert groups have suggested that since there is no ideal anticoagulant regime, women should be given the information and encouraged to choose their therapy[4]. Whilst the concept of 'informed choice' is appealing, there is a need for accurate information on which to base this choice. The aim of this study is to provide population based estimates of the incidence of maternal and fetal complications with the different anticoagulant regimes. This would help optimise the future management of pregnant women with artificial valves, to obtain the best outcomes for mother and baby.


  • To use the UK Obstetric Surveillance System to describe the incidence, management and outcomes of pregnancy in women with artificial heart valves in the UK.
  • To use this information to develop guidelines for their optimal management.

Research questions

  • How many women in the UK with a prosthetic artificial heart valve become pregnant?
  • What is the incidence of thrombotic complications in women with artificial heart valves in pregnancy?
  • What are the outcomes of pregnancy in women with artificial heart valves?
  • What is the incidence of other serious maternal or fetal morbidity?
  • Does the incidence differ with different anticoagulants and different regimes?

Case definition

All women with artificial mechanical prosthetic heart valves in the UK, who become pregnant during the study period, irrespective of the outcome of the pregnancy.

This includes any woman in whom one or more heart valves have been replaced with an artificial mechanical prosthetic heart valve e.g. Starr-Edwards ball in cage, Bjork-Shiley tilting disc or St Jude's bi-leaflet valve.


Women with a bioprosthetic valve eg Carpentier-Edwards, Medtronic Intact or Hancock, women with a homograft or women who have had a valvotomy or valvoplasty (unless they also have an artificial mechanical prosthetic heart valve).


This study is funded by Wellbeing of Women.

Ethics committee approval

This study has been approved by the NRES Committee Yorkshire & The Humber - Sheffield (study reference 13/YH/0048)


Dr. Sarah Vause, Prof. Bernard Clarke, Dr. Clare Tower, Dr. Charles Hay, Central Manchester University Hospitals NHS Trust; Prof. Marian Knight, NPEU.

Download the Data Collection Form (DCF)

UKOSS Prosthetic Heart Valves Form


  1. ^ Sadler L, McCowan L, White H, Stewart A, Bracken M, North R. Pregnancy outcomes and cardiac complications in women with mechanical, bioprosthetic and homograft valves. BJOG 2000; 107:245-253.
  2. a, b, c Chan WS, Anand S, Ginsberg JS. Anticoaglation of pregnant women with mechanical heart valves: A systematic review of the literature. Arch Intern Med 2000; 160:191.
  3. ^ Roberts N, Ross D, Flint SK, Arya R, Blott M. Thromboembolism in pregnant women with mechanical prosthetic heart valves anticoagulated with low molecular weight heparin. BJOG 2001; 108:327-9.
  4. ^ Consensus views arising from the 51st Study Group: Heart Disease in Pregnancy Heart Disease and Pregnancy Eds Steer PJ, Gatzoulis MA, Baker P. 2006 RCOG Press.

Updated: Tuesday, 17 January 2023 18:37 (v6)