What are my chances of twins?

I got pregnant (4.5 years after our first childn) with first IUI attempt after 50mg of clomid and progesterone suppositories after the IUI. My hcg levels at 5weeks were 4641. I'm already showing a bump at 6 weeks. My first OB scan is tomorrow but I'm soooo curious... Just for fun, what do you'll think? Singleton or twins? Thank you in advance. Will post what the scan shows tomorrow!