due date changed

[JaJu14]

I was certain of my due date as I have regular periods (28 days) and when I had my son I was right about my due date then.
The scan put me forward 4 days so I'm going by that date but I'm confused as to how I'm 4 days ahead when I know what day my last period was lol

Any ideas?

Don't worry. My due date moved twice and he arrived early.
When I worked out my dates he was due on the 21st, when I had my booking in apt his due date was the 15th and then my dating scan put him to the 18th... He arrived on the 9th.
I don't think it's an exact science, just a guesstimate on dates of last bleed and sizes at scan. I wouldn't worry too much x

It is based on the measurements they took of your baby at the scan. That is the date they will use from now on not one based on your last period.

They base it just on measurements at your 12 week scan. I know exactly which day I conceived (was tracking) and the scan dates put me 5 days ahead of that. I don't think it really matters as long as I don't go very overdue and get pressured into an unnecessary induction.

Your period may be regular but your ovulation may vary. Plus sperm living for a number of days and other factors which mean date of conception can't be pinpointed.

The measurements used give you a due date based on averages etc but nfortunately the babies in question don't get the same memo so just come when they bloody feel like it.

Isnt it amazing they can redate at a scan based on size but when they arrive they are all manner of lengths and weights!

5 women can start their periods on the same day and have a normal 28 day cycle. One might conceive on day 10, one on day 11, one on day 15, one on day 17 and one on day 19. All would have different due dates.

Plus scans can be a week out anyway.

A few days don't matter. The baby will likely come between 37 and 42 weeks. The due date isnt when your baby is likely to come, it's just a way of arranging care.

Isnt it amazing they can redate at a scan based on size but when they arrive they are all manner of lengths and weights

Development is pretty universal in the first trimester. Genetic and individual differences kick in after the dating scan.

I had three different days depending on the way the GP and midwife calculated and the scan throw another one up.

In the end I was a week - 10 days overdue so whatever they say take it with a pinch of salt.

Your last menstrual period gives a rough idea on when you may of conceived but it's pretty irrelevant after your 12 week scan.
Unless you know the date of conception or had been tracking ovulation.

Thanks guys, I was not tracking ovulation and never have. Both my babies were "happy accidents". I've no idea when son was concieved as was withdrawing (obvious fail) and with this one was a split condom so I know it was day 9 after period (didn't take morning after pill as I thought it wasn't fertile period anyway)

It just thrown me as my date never changed with my son lol

Thing is, the split condom may have happened 9 days after your period started but you may not have ovulated until 6-7 days later - sperm can live up to 7 days after ejaculation in a hospitable environment!! Then it can take another 5-7 days for the fertilised egg to implant in your uterus so, your dates could end up almost 2 weeks after you know you last had sex.

So that is almost spot on unless I've got confused somewhere.
Going by the last period, 28 day cycle thing it's assumed you will ovulate on day 14. You had sex day 9 and you have been dated 4 days ahead so looks like you ovulated early.
Scan dates can be a tiny bit out but it sounds bang on.

Do if you conceived day 9 then that’s right, you should have been moved forward.

Ok thank you. Guess I ovulated early then.