Is my brother the father of the child?

Is he the father?

My brother had sex with his ex-gf last feb15 and March 2 the girl said that she is pregnant and it was my brother's. According to the girl her last period was Jan 19. As to the ultrasound details we don't know. She then gave birth Oct20. Is my brother the father of the child? Because if we based it on the time they only had their encounter which is feb 15, the baby should be born around November. We really need clarifications regarding this matter. Thank you so much!