It wasn't relayed to doctor because BSR lied to the doctor and his medical assistant when she gave the date or her last period. He did not have accurate information to determine approximate conception.
According to OBGYN testimony, BSR told both doctor and medical assistant that her last period was in March/ April 2018, but her urine tested positive for pregnant. Also, she never reported to her OBGYN that she had irregular periods. In fact, I believe she told them all was normal.
Later at police department, BSR told her dad that Tre was the father -- a fact undisputed by all parties. Tre testified they had unprotected sex in August 2017--prior to him starting his freshman year at Wright State.