12 week ultrasound reliability/short cycles

[pearlycat1]

Hiya. I’m just wondering how accurate everyone’s 12 week ultrasound was for their pregnancy, like in relation to their cycles. My cycles are 19 days, so assuming ovulation happens earlier - the scan will measure bigger?? Help lol

The 12-week ultrasound is usually the one used for the final due date, as it's most accurate. But the due date is also just a guess, so not super reliable either! (I think something like 10% of babies are born on their due date.) If it's out, it will probably be just a few days.

With my first, which was a natural pregnancy, the due date moved from the 18th to the 15th, and baby was born on the 13th. (I'd also had a sweep, which could/probably moved things along slightly.)

With my current pregnancy, which is IVF, so I have very details dates, the midwives' due date was the 8th and the clinic's was the 2nd; the 12-week scan put it at the 4th. If I remember when baby arrives, I'll update with their birth date!

@FluentTealGuide thanks for your response! And goodluck with your pregnancy x

I was having really irregular periods so my '12 week' scan was actually at 9 weeks. I had suspected this would probably be the case and was invited back for a second scan. They just figure out how far along you are at that scan and adjust dates accordingly.

Don't worry, the scan is partially to date the pregnancy as well as check progress. They can work out how far along you are by how big the foetus is. The 20 week one is more important that it happens at a specific time.