In an age-structure pyramid, the most critical age span for women in order to determine the current fertility rate potential is

In an age-structure pyramid, the most critical age span for women in order to determine the current fertility rate potential is: 15-49
Past this age, Women's uterus will become significantly weaker compared to their younger ages. This make them unable to sustain the living of their infants through natural reproductive method. On top of that, they will also stop ovulating when surpassing this age group.

Pretty sure the answer is Tripartite