How do dates work with late ovulation/long cycle?

[bigblueboots]

Hi everyone, we have just found out a couple of days ago that my DW is pregnant for the first time and I am in excited research overdrive!

I've learned about dating that its counted from the beginning of your last period, but that seems to assume a 28 day regular cycle. DW has irregular (28-40+ day) cycles and we only really started tracking ovulation properly the month that we conceived.

She ovulated on CD22 and now we're 13DPO, so CD35. So, does that make her officially 5 weeks pregnant (because its 35 days since last period), even though ovulation only happened less than 2 weeks ago? Or should we calculate as if it was a 'normal' 28 day cycle with ovulation at CD14, so she'd be 4 weeks now?

(I know it probably doesn't matter much but I need something to occupy me in the long wait before a first appointment and scan and everything!)

My cycles are long so I always knew I was at least a week behind the date based on my LMP. At the 12 week scan they readjust your weeks / EDD based on your measurements. Congratulations!

I think they calculate it as a 28 day cycle and from you last period, then adjust it when necessary at your 12 week scan

I was a late ovulator and they still used the lmp to book the scan in. It meant that I wasn't far gone enough for them to properly measure anything so I had to go back for another one. To be honest I didn't really mind as it meant we got re-assurance that there was a heartbeat earlier than expected and got an extra picture of the baby

She is nearly 4 weeks pregnant but they will take the lmp date until scanned. The scans can be a week out either way though so you might find that you measure nearer or further away than you're expecting anyway.

I just told them a different lmp date which matched when I actually ovulate (so 14 days before conception) to ensure that my first scan fell at the right time.

I have similar and my hospital offered an early pregnancy scan. My cycles are 30-70days though

If you know the date of ovulation, great! Take 14 days off that and use that in place of LMP date. I told my midwife my LMP was this date, but I had confirmed ovulation on day 12 so I was actually slightly further along my pregnancy. I went for an early scan which confirmed my maths, but I'll get a "proper" due date at my 12 week scan.

Due dates are calculated based on period start dates as this is an observable event for most women, and uses a "typical" 28 day cycle of 14 days follicular and 14 days luteal. Longer cycles have more follicular days as the luteal days are pretty fixed. So the LMP just needs to be adjusted to later

Thanks everyone, really appreciate the help. We're on the midwives' list now, so will just have to wait and see when we get to scan stage if my working out date was right or not!

Off to find a new thing to research this week