How can I find words with three **or more** vowels **of the same kind** with a regular expression using back referencing?

I'm searching in text with a 3-column tab format "Word+PoS+Lemma".

This is what I have so far:

```bash
ggrep -P -i --colour=always '^\w*([aeioueöäüèéà])\w*?\1\w*?\1\w*?\t' filename

```

However, this gives me words with three vowels but not of the same kind.
I'm confused, because I thought the back referencing would refer to the same vowel it found in the brackets? I solved this problem by changing the `.*?` to `\w*`.

Thanks for the help!