The spelling of the word "Birtha" can be a bit confusing. The pronunciation of the word is /ˈbɜrθə/, with the stressed syllable being "berth" and the vowel sound being the mid-central unrounded vowel. The letter "h" is pronounced, but in some dialects, it may be silent. It is important to note that this is not a very common word, and it may vary in spelling depending on the context or language. Therefore, it is always best to consult a dictionary or other reliable resources when unsure about spelling.