From Halopedia, the Halo wiki
Because the fertility cycles of female San'Shyuum are short and few and far between, it is difficult for San'Shyuum to have children. The birthing period is a festival celebrating those who have successfully managed to sire offspring, with mothers proudly showing off their broods. Unfortunately, given the difficulties in San'Shyuum reproduction, birthing periods only occur once or twice an Age.
In celebration of the birthing period, the upper inhabited levels of High Charity are lined with garlands of flowers, fireworks are set off, and music and singing are provided for entertainment. The event is also ushered in by an invocation, presented before the High Council, usually by a high-ranking ministerial official. It is unknown if this means all San'Shyuum give birth at the same time or not.
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