Can someone pls help with dating question?

[mrssunshinexxx]

Last period 17th Sep midwife has put me as 6+5 however I know when I ovulated because I was tracking (2nd Oct) so that puts me as much less I booked in an early scan when I thought I would be 8+1 I asked the scan guy when Isit best to have them likely to see a heartbeat and can have it externally he said after 7 weeks so thought great but then I've been over thinking my ovulation date and worked out from that I'll actually only be 6 weeks exactly on that scan date ... can someone shed some light because obviously I know I wasn't pregnant on 17th Sep and don't want to get to the scan and be to early to see heartbeat should I put it back?

Feel like I'm bound to get put back a fortnight at 12 week dating scan

When they calculate the dates, it starts on the first day of your last period. So you aren’t actually pregnant for the first 2 weeks (assuming it’s the average cycle and you ovulate 2 weeks later). So when you are 12 weeks, that’s 12 weeks since your last period, but only 10 since you ovulated/fell pregnant.

Pregnancy is dated from your last period and not from your ovulation date. Think of it as your ovulation date plus 2 weeks as you ovulate roughly 2 weeks after your period begins.

Your ovulation date (OPKs aren’t exactly) is about 2 weeks (15 days in your case) after your period so yes, that would put you at the stage the MW has told you even accounting for your ovulation date, so you should be around 8 weeks for your scan.

Be prepared that even then you may need an internal scan even at 8 weeks.

Thank you

Z