- a history of subfertility
- levels of progesterone
- levels of hCG
- the length of the fetus
- how much bleeding had occurred
- gestational age of the baby
However two of these factors. the amount of bleeding and levels of hCG were combined to create the "Pregnancy Viability Index" (PVI). PVI was able to accurately predict the pregnancy outcome in 94% of women who had ongoing pregnancies.
European Society of Human Reproduction and Embryology (ESHRE). "Outcome of pregnancies threatening to miscarry predicted accurately for first time."