Dating pregnancy with an irregular/long cycle

(11 Posts)
busylady99 Mon 10-Dec-12 17:00:29

I understand that doctors date pregnancy from the date of the last period but does that still work out if you have a longer cycle? I seem to be about 35 days (though it varies) so if I am pregnant (got the faintest line today but re-testing in the morning as I fear I was seeing things) I would be 5 weeks pregnant officially and the baby would officially be 3 weeks but actually only be 2 weeks old.

I'm plainly getting ahead of myself, but due to a spinal condition I will be having a CS and I believe that ELCS are usually carried out a few weeks before the due date. If the ELCS is, say 'officially', 2 weeks early it would actually be 3 weeks early for the baby. Does that make sense?

Or am I just being mental over nothing and they amend the dates at the dating scan??

Only possibly pregnant for a few hours and I've already gone nuts wink

jennimoo Mon 10-Dec-12 21:14:01

They'll amend your dates at the 12 week scan and I expect your can will be scheduled based on that as measurements at that stage are pretty consistent across pregnancies. Of you're sure when you ovulate you could always just tell dr that your last period was 2 weeks before that ;)

jennimoo Mon 10-Dec-12 21:14:23

Can = cs...

cogitosum Mon 10-Dec-12 21:15:50

On most online due date calculators now you can put your cycle length and it'll use that to work it out.

So if you have a 35 day cycle (like me!) and your lmp was 8 weeks ago you'll be 7 weeks.

cogitosum Mon 10-Dec-12 21:16:49

http://www.nhs.uk/conditions/pregnancy-and-baby/pages/due-date-calculator.aspx

jinglebellyalltheway Mon 10-Dec-12 21:16:52

the only way if you don't know your ovulation date is to get an early dating scan. Then they can book your 12 week scan for the correct time, the window for the downs syndrome screening is pretty narrow so if you want those tests you need your 12ish week scan and bloods done at the correct time

ReindeerOutdoors Mon 10-Dec-12 21:17:37

They do amend edd at dating scan but a lot of online calculators allow you to adjust cycle length, even if you're irregular if you put in 35 days it would be a closer guess than based on a 28 day cycle. So if you want to get a better idea of what might come up at dating scan, you could use one of these.

jinglebellyalltheway Mon 10-Dec-12 21:18:21

dating by LMP plus cycle length isn't particularly accurate either, with a longer cycle it just means more possible weeks where you might have ovulated, those calculators will only tell you when the average conception was for people with your cycle length, not date YOUR pregnancy

ReindeerOutdoors Mon 10-Dec-12 21:18:25

X post with lots of people smile

wanderingalbatross Mon 10-Dec-12 21:25:53

It has happened to me (twice) that my dates based on LMP were wildly out due to long and irregular cycles. Both times they scanned me, said I was too early and rescheduled a 12-13 week scan. The due date from that second scan was then used for the rest of the pregnancy.

HaveIThoughtThisThrough Wed 12-Dec-12 12:36:14

(Changed my nickname from Busy)

Thanks everyone for all the information, you've put my mind at rest.

I took another two tests and I've got my BFP so I'm over the moon. According to the OV predictor, my due date should be 20th August.

( Jennimoo, sorry, I don't understand the can=cs post - I'm probably being thick? Is it another acronym?)

Join the discussion

Join the discussion

Registering is free, easy, and means you can join in the discussion, get discounts, win prizes and lots more.

Register now