Table 1. Selection criteria for the studies included (PICOS)
	Included	Excluded
Population	Women with repeat abortion.
Intervention	Low molecular weight heparin treatment
Comparison	Expectant Conduct
Results	Primary: Live births, spontaneous abortion, continuous pregnancy beyond the 20th gestational week, implantation rate.
	Secondary: clinical pregnancy, premature birth, multiple pregnancy, congenital abnormality, hemorrhage, preeclampsia, placental premature detachment.
Type of study	Double-blind and quasi randomized studies	Systematic review and meta-analyzes, case control study, case reports, comments, nonrandomized