Hello everyone. The last period was on July 29th, resulting in a…

Hello everyone. The last period was on July 29th, resulting in a gestational age of 9 weeks. My cycle is 45 days and ovulation occurred much later, at 7 weeks. How do I explain this to doctors during an ultrasound? They always ask for the date of the last period. Based on that, it will appear that there's a delay in the child's development. Should I say what it is as it is or say that the period was August 16th, which falls within the due date. Or should I say the date of conception, knowing for sure when it happened.