Toharot, Chapter Four, Mishnah Thirteen
“And a condition of doubt concerning sacrifices”if a woman has experienced five doubtful cases of miscarriage or five discharges of doubtful zivah she brings only one sacrifice and may then eat other sacrifices, she being under no obligation to bring the remainder.
The final mishnah of our chapter explains the last case of leniency with regard to doubt. The entire mishnah is found in Keritot 1:7. Below is my explanation from there:
There are two situations that are described here.
1) A woman had genital discharge for three consecutive days once a month for five months and she doesnt know if these occurred during her menstrual cycle, in which case she was not a zavah and does not need to bring a sacrifice, or not during her menstrual cycle and she is a zavah and does need to bring a sacrifice.
2) She had five miscarriages and she doesnt know whether what she miscarried counts as a birth and she must bring a sacrifice or doesnt count as a birth and she does not bring a sacrifice.
In both of these cases, the woman might be liable for as many as five sacrifices (each consisting of an olah and a hatat) or she might not be liable at all. The rule in this case is that she needs to bring only one sacrifice and then she can eat any sacrificial meat, as is always the case when a woman brings a sacrifice for being a zavah or for giving birth. While she can, if she wants, bring four more sacrifices, she need not do so.