Very few women decide to become nuns in Burma : indeed, women do not get the ordination. While monks are fed by crowds of believers hunting for merits, nuns are turned into real beggars. Women are deemed to be spiritually inferior to men (they are often banned from the highest platforms of temples, for instance. They also can't put gold leaves themselves onto Buddha images: they have to ask a male attendant to do so). In the cycles of reincarnations, the "woman form" is considered an inferior state to the "man form". The social status of nuns is clearly inferior to that of monks, as well.
Buddha himself hesitated a long time before deciding that women could become nuns. His mom Mahapajapati eventually managed to convince him. Nuns were not given the same status as monks, but they were allowed to establish their own distinct order. They had to respect 8 rules which all contained the notion of male supremacy over woman. What's more, their monastic code had 500 rules while the monks code had (and still has) 227 rules only (!). The nun order didn't make it thru history and finally disappeared at an unknown stage.
There are still religious communities of nuns, observing daily about 12 rules (that which secular believers observe only on special occasions) These women are called "thilashin" in Burmese (the English word nun is misleading). They share their day between cooking for monks/altars, praying and meditating. They also sometimes take care of orphans and elderly, or teach young girls. Some study religious texts as well: they are allowed to sit the same exams as the monks.
If monks are present throughout Burma, nuns are a rarer sight: society indeed tends to discourage women from entering religious life.

For more details on the living conditions of women in modern Burma, you can turn to "Birmanie, côté femmes", by Claude Delachet-Guillon, Olizane, Geneva, ISBN 2-88086-291-4.