Every month, the Oxford English Dictionary adds new words. In June, doula (noun) was one of the new words added.
In case you are curious how they decide what to add:
The OED requires several independent examples of the word being used, and also evidence that the word has been in use for a reasonable amount of time. The exact time-span and number of examples may vary: for instance, one word may be included on the evidence of only a few examples, spread out over a long period of time, while another may gather momentum very quickly, resulting in a wide range of evidence in a shorter space of time. We also look for the word to reach a level of general currency where it is unselfconsciously used with the expectation of being understood: that is, we look for examples of uses of a word that are not immediately followed by an explanation of its meaning for the benefit of the reader. We have a large range of words under constant review, and as items are assessed for inclusion in the dictionary, words which have not yet accumulated enough evidence are kept on file, so that we can refer back to them if further evidence comes to light.
Just goes to show that the role of doulas is gaining popularity and prevalence!