Need to optimize a peg.js to get some words from a sentence appropriately

I need to get a specific word in a sentence using peg.js. What I need to get from the sentence is a word like rth when there are spaces around. But here you see that birth is going to be fetched. The reason is “rth” is part of “birth”.

for example : rth:23 kian ht:25 kg 12 ft and wc:36 birth:27