Confused by how pregnancy is dated

[elmo1980]

I know this has been done before but I can't find older threads.

Based on the first day of my last period I am now 13 weeks pregnant. However, because my cycle is slightly longer than average (34 days) my midwife has pushed me back by 2 weeks.

My first scan isn't for another 2 weeks but when I was looking through my diary earlier I thought it would be impossible for me to be 11 weeks as that would mean the week I conceived was the week I found out I was pregnant.

Plus i know exactly which week I conceived and it was 2 weeks after my period.

Morning sickness is still horrific too so that's confused me even further!

Can anyone explain this or is it one of those annoying mysteries of pregnancy?

I think they take it from the start of your last cycle...

Some calculators allow you to account for cycle length.

The two week thing is based on a 28 day cycle, ie ovulating two weeks into your cycle.

Eg, I am currently 5 weeks pregnant, ie I ovulate/conceived three weeks ago. But based on lmp, as have a 35 day cycle, I would be 6, which isn't the case.

Sorry, that was a bit muddled, but hopefully you get the drift!

If you know that you conceived 2 weeks after the start of your period, then that's 13 weeks. The midwife is being weird. I'm sure it'll get sorted at the first scan.

The pregnancy starts from the day you ovulated, which could be up to 7 days after you had sex (this is how long sperm can survive inside you). The first EDD is an apporximation since the midwife doesn't know your ovulation date, neither you can tell for sure based on the length of your cycle (although the longer the cycle, the later the ovulation day). When you do the first scan you will get a more accurate EDD.
Don't forget thta the first week of pregnancy, the week the sperm fertilised the ovary, is week 0! So 1 week pregnant means that you have just completed 1 week of being pregnant.

Dates based on conception and periods are just a rough idea. When you have a scan they can date the pregnancy accurately and go from there.

No, the week the egg is fertilised is the end of week 2. You're technically not pregnant yet for the first two weeks. It's just gearing up for ovulation.

A 34 day cycle doesn't seem long enough to bother pushing back EDD to me. I'm not a midwife though!

Have you had your first scan? If you want nuchal screening it needs to be done by a certain gestation.

I mean, you don't want them to delay it and then find out you were right and it's too late.

Alexandra, in the UK it isn’t based on gestational age. It’s calculated from the last missed period so 2 weeks earlier.

There’s only a discrepancy if someone has very log cycles and ovulates say on day 20 or later as that makes it -1week or more.

OP, you’re accurate as you tested early and by the time you get a bfp you’re at the very least 3.5 weeks along.

OP - is there anyway you can ask for your scan to be brought forward? If you will be 15 weeks then it will be too late for nuchal screening.

I've tried to get an earlier scan but no appointments. A bit worried as if I'm correct with my dates I'll be 15 weeks for first scan and I thought that was a bit late.

I would be quite assertive about it in that case. This happened to me with my 20 week scan and the midwife told me that they would have to fit me in, even as an emergency.

Could you go private?

That's outrageous that they'd keep you waiting so late if that's too late for nuchal screening! Have you considered a private scan? Or making a complaint so that they can fit you in?

Bugger we are having the nuchal screening this time round so it's likely going to be too late. I'll give them a call tomorrow to explain and see if they can get us in earlier. I guess they are going off the midwife notes.