In reasonable conditions, the majority of female tetras will fill with eggs. The body widens and deepens relative to males. If the conditions are right, males will drive the female and they will scatter eggs. She will then start to fill again.
Depending on the species, she may scatter eggs almost continuosly, a few at a time, or may wait until she has a good sized clutch to deposit.
If a female fills with eggs and the conditions are not right for spawning, the eggs tend to be reabsorbed and new one develop later.