Due date change

[Teeliaxx]

I had my first scan & expected to be around 12+4 days with a due date of 11 November, however I measured at 13 weeks so my due date has changed to the 7th of November. Does anyone know why this might be? It’s so strange because my conception calculation I could have still conceived around the same time? So why would it change ..

It's very usual for date to be refined following 12 week scan. It's all an estimate in any case. Your first date was calculated from last period, your new date from measuring foetus. Neither can tell you exactly when you conceived or exactly when your baby will be born.

Implantation generally occurs between 6-12dpo which has a knock on affect of it. Some grow a little faster or slower too. I was our way ahead with my first and she was born at 8lb 4 at 37w by their dates but 34w after conception so 36 weeks.

Your original date would be from your last period. However, each pregnancy is different and the fertilised egg can take less/more time to implant and begin developing.
When they measure you it's a more accurate due date than you originally had as it goes off baby's measurements.

Both of mine I was moved 6 days forward. I think it could be that I ovulated earlier than average. Plus there is margin for error as the measurements are tiny. Dc1 arrived 6 days late so on due date from last period date.

I’m the same. Original due date was November 15th. After the first scan it changed to November 8th. It’s to do with the baby’s size at the scan

Scans are only accurate to plus or minus seven days so I'm surprised they changed your due date. If you are sure of your dates then I would work on your date.

My LMP due date was 24th July... at my first scan I was moved to 4th August, then later in pregnancy it was moved back again and baby came 28th. Baby will come when baby is ready xx

Scan dates are not accurate. I had an IUI procedure so I knew exactly when I conceived and my fertility clinic told me that my due date was 16th September. My local hospital told me that my due date was 11th September which couldn't be accurate but this is what they insisted they had to use. My son was born without induction on 22nd September so 6 days after my fertility clinic told me and 11 days after the hospital predicted. So definitely not accurate.

It’s all estimated anyway? Better to treat it as a time frame rather than 1 date

Thankyou all for the clarity. I think the only reason it through me off is because I know when I had intercourse.. keeping in mind sperm can live for 3-5 days! Even with the conception calculators , whether the due date is 7 or 11 I still conceived around the same time it’s so confusing! This is my second baby first will be 7 when this one is born & I can hardly remember anything! Feels all new again but thankyou

It’s all an estimate. I measured my ovulation using opk and bbt so I know within a day what I should have been. The nhs dating scan put me two days ahead of that which is technically not possible but it’s just that my baby was slightly growing ahead. They date based on measurements and to be honest only being two days out for mine is pretty close.

Hi @Teeliaxx same thing happpened to me, my date was changed. I think they go by measurements.
Congratulations on your pregnancy xx