The gemara says that a woman who gave birth to a boy and will finish her 40 days, (7 temai layda and 33 yemay tohorah), on the night of Pesach can be among the menuyim for the korban even though she's technically like a tvul yom. Why is this so? The posuk says that she can't touch any kodesh until she has heerev shemesh after the 30 days (ad mlos y'mei tahara). Normally a korban can't be brought for anyone unless the person is tahor at that time. Even though a tzibbur can bring the korban pesach if most of them are tamei that's referring to temai mes, not other types of tumah.

B'kavod,

Sam Kosofsky