How many weeks am I?

[MinnieMouse32]

I have a really irregular cycle (anywhere between 35-60+ days)
And am currently pregnant!
The date of my last period was 12th October, and had a positive ovulation test on 1st November (we had sex on this day and around it, so will have concieved then)
So how many weeks am I!? All the online calculators are saying different things!

8 weeks as a guess

The start of pregnancy is dated from two weeks prior to ovulation. Ovulation is officially cycle day 14. So if you got a positive opk the day before ovulation you ovulated on 2nd Nov. So if 2nd Nov was CD14, CD1 was 20th October. Use the NHS due date calculator and tell it your cycle is 28 days long and your last period started on 20th October.

My cycle isn't 28 days though, it is very varied from 35-60 days
So would this be right?

Yes I know, but you have to pretend it is 28 days to make the date calculator work! If your cycle WAS 28 days you would have had your period start 14 days before ovulation, so 20th October is your period date IF you had a 28 day cycle.

My cycles used to be up to 70 days long. When I fell pregnant with my ds I had ovulated around day 26 (I used to do bbt tracking). So I counted 14 days back from the day I knew I ovulated and told the midwife that was the first day of my last period. My dates were spot on and my waters broke on my due date. If I'd have given the midwife my true first day of my lmp, my dates would have been way out!

So follow the advice of a pp and count backwards,

Congratulations!!

Ignore ovulation date for now. Until a scan and measurements you can only go from period date. 12th October makes you 9+2 today with a due date of 19 July.

Your first scan will take measurements that will date you more accurately and given your irregular cycles probably change your due date and weeks. But until then you only have the 12th October to count from.

Initially, they will use the LMP date just to start calculating scans and appointment dates etc but you're right that this won't be accurate if you have long and/or irregular cycles.

I had an early scan when LMP said I would be 8+2 but I actually only measured 6+1.

The 12 week dating scan is when you'll get your most accurate measurements and official due date. By the 12 week scan, I was 10 days behind and I've stayed there ever since (now 26 weeks)

But by LMP the pregnancy will be 8 days further on than it actually is? So that's fine if OP is given a scan date bang in the middle of the screening window, but a pain if she is given one early in the window. If the hospital do a scan at what they think is 12+0 (by LMP), then OP will actually be less than 11 weeks pregnant and will miss the ideal dating window and be unable to get screening for Down's etc if desired. She will have to go back for another scan, which would be a waste of the hospital's time and OP's time. Why bother, when she is perfectly able to date the pregnancy accurately by ovulation?

Don't mean to sound snarky at all! But I'm really against wasting NHS time. Also, for some areas of the country a scan might mean OP doing a 200+ mile trip! She wouldn't want to do two of those 😂

She might be able to argue the hospital into giving her a later scan date but I'm not sure they will book in anyone based on any date other than LMP.

She could lie and give her LMP date as a week later if she wants to but I wouldn't recommend that.

I have tracked my ovulation twice which resulted in pregnancies and both later than the typical cycle/ovulation lengths (eg day 14 to ovulate). Once I ovulated on day 24 when I conceived with my son, and this time I ovulated on day 18.

I did as pp have said and worked out an estimated LMP by going ovulation-14 days. Interestingly the 12 week scans have been very close. Both times they put me two days ahead but that’s still very close in the grand scheme.

Why not? OP has more information than they do and can make a better call.
I have told them a fake LMP date with all four of mine, as my dating scan would have been way out if I hadn't. I had very clear bbt charts though so I was confident of my dates. When I had a midwife prepared to think outside the NHS party line I did admit I was doing this and she was fine with it.

I probably wouldn't because I'd rather have a scan too early and have to come back again than risk it actually being too late because the dates were unreliable and miss a testing window.

But if OP is absolutely confident of her ovulation date then by all means lie about LMP and get the first scan a bit later. No skin off my nose.

I'm 26 weeks pregnant now and my due date is 10 days different to what my LMP date would say. All my antenatal care abroad has confirmed this so now, when I go to my first appointment in the UK this week, I'm just going to give them an amended LMP date to reflect the 10 day difference.
It's easier that way.

Surely if you've got to 26 weeks you've already had dating scans which have given you an amended date anyway. So you don't need to lie about the LMP, it's been superseded by scans. As OP's will be.

Sorry I wasn't particularly clear in my post, I've been living abroad up until now so all antenatal care and 4x scans etc were done overseas.
I am confirmed as 10 days behind LMP.

I have my first UK appointment this week and will be giving them an amended LMP date so all records are right with my current true gestation and the rest of my appointments can be booked in accordingly.

To the OP, I would only do this if I was absolutely 100% certain of my dates

No I got that. I'm just surprised that to book in with the NHS you'd need to lie about your LMP and that they wouldn't just accept your previous scans and results of them. That's different to OP who hasn't had any scans.

That's OK to be surprised, I guess most people haven't been in this situation. I've still had to self refer and have my initial 'booking in' appointment this week. I've given an amended LMP date on the paperwork and added a note regarding what ante natal scans I've had and confirmed due date etc. As I said, it keeps it all simple.

I did edit my post after pressing send with a comment to the OP