Confused with skull theory

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Hey ladies! So skull theory has me sooo confused. I'm 14 weeks today and I've been trying to see what to look for with my ultrasound from last week. I know it says that a girls head is usually more round by I look back at ultrasounds from my previous pregnancy and the skull is so much more round and it was a boy. Here is an old ultrasound from my first pregnancy 
And here is one from this pregnancy
Thoughts??