Clexane is for clotting - it prevents clots forming but it also has an anti-inflammatory property which may be important in conditions that have an auto-immune function. There may not be any abnormalities found as such or there may be low levels in blood test results. If you were tested when pregnant, the results can be different to if you were tested when not pregnant. Some women have no known cause or things such as NK (natural killer) cells which is still in the early stages of identification and treatment. There are many conditions that are not yet named that impact on the pregnancies of many women.

A few articles for you to check out if you want to.

http://www.gfmer.ch/IAMANEH_ESMANEH_...exane_2006.pdf
Elsevier
Informa Healthcare - Journal of Obstetrics & Gynaecology - 28(3):280 - Summary
Early Pregnancy - Google Books
The effect of thrombophylaxis on pregnancy outcome in patients with recurrent pregnancy loss associated with factor V Leiden mutation - Younis - 2005 - BJOG: An International Journal of Obstetrics & Gynaecology - Wiley Online Library