Ava is designed to help you time intercourse around the fertile window. If you are not ovulating or if you do not have the hormonal variations associated with ovulation, Ava will not be able to track your fertility.
There are a variety of reasons why you might not be getting your period but in many cases, this means that you are not ovulating.
Ava is designed to detect your fertile window which includes the day of ovulation and the five days before predicted ovulation. If you are not ovulating, you do not have a fertile window for Ava to track.
You might find it interesting to track your sleep, stress, temperature, and pulse rate on Ava but it will not be able to provide accurate fertile window predictions if you are not having period.
There are several possible reasons why you might not be getting your period. PCOS is a common one and hypothalamic amenorrhea is a less common one. You can read more about hypothalamic amenorrhea here.