Welcome to the site.
Giving statistics on you as an individual is really difficult as I dont have your whole medical histories and even if I did, although I am a Registered Nurse with experience in this field, I am not a medic.
I can give you very general statistics that may help but would suggest you seek a specialists opinion to verify this in line with your own history.
The risks are as follows if you have - (reference 2)
Previous pre-eclampsia 7 times more likely of recurrance.
Antiphospholipid antibodies 10 x more likely
Diabetes 3.5 x more likely
Family history 3 x more likely
Multiple pregnancy(twins) 3 x more likely
First pregnancy 3 x more likely
Age 40 or more & already has children 2 x more likely
Age 40 or & more first pregnancy. 2 x more likely
BMI raised at booking 2 x more likely
Diastolic bp at booking 2 x more likely
There was a school of thought that felt a change of partner may change the risks and while it seems there is still some truth in that statement due to the exposure of the antigens in partners sperm it was felt that in general and change of partner coincided with a longer interval between pregnancies and in fact it was this interval that increased the risk. It is thought that an interval of 10 years or more increased the risk.
Aspirin is recommended as it in the PARIS review 'low dose aspirin offered moderate benefits of prevention of pre eclampsia & its related conditions but it could not define which sub groups benefitted most & which did not'. (1)
The use of heparin is decided by your Consultant obstetrician often in partnership with a haematologist. You will need to be tested for a variety of 'sticky blood syndromes' which is known as a Thrombophilia screen. This is likely to include conditions like Anti-phospho-lipid syndrome (APLS), thrombophilia and Leiden Factor V.
The use of heparin if indicated will mean lots of blood tests to check your blood is not too thin.
The use of donor eggs increase the risk by about 4x even if they are from a family member, eg your sister, (about 2x more likely) increase the risk of developing PE and have posted separatley about this.
I really hope all thsi helps Suzie, but if you have any more questions please do feel free to fire away! If you would prefer to keep things more confidential I am happy for you to PM me.
Reference (1) http://www.aspirin-foundation.com/suitability/documents/070531Aspirinforpre-eclampsia-revisedAFwebsitepaper.pdf
Reference (2) Risk factors for pre-eclampsia at antenatal booking: systematic review of controlled studies
Kirsten Duckitt and Deborah Harrington
BMJ 2005 330: 565.