PROBLEM: Does Th1/Th2 balance determine pregnancy outcome, and if so, what determines Th1/Th2 balance in pregnancy?
METHOD: Review and synthesis of existing data.
RESULTS: A bias toward Th1 is strongly correlated with pregnancy failure in mice and humans. Pregnancy usually shifts the balance toward Th2 and placental factors/progesterone and progesterone-stimulated CD8+ T cell production of suppressor factor; TGFβ2 and IL4/ 10 may be responsible. The bias toward a Th1 response may result from intracellular parasitic infection and other as yet undefined factors.
CONCLUSION: The Th1/Th2 balance thesis appears to be valid.