00364nas a2200157   4500000000100000000000100001008004100002100001300043700001500056700001100071700001400082245007700096300001100173490000800184022001400192       2014                            d1 aI. Matok1 aL. Azoulay1 aH. Yin1 aS. Suissa00aImmortal time bias in observational studies of drug effects in pregnancy  a658-620 v100  a1542-0752