Confused about dates after 20 week scan

[Mrs Dragonfly]

Earlier this week we had our anatomy scan and found out we're having another little girl! but the doctor confused me about the dates.

When the tech was asking my gestation and due date before the scan started I said 19 weeks because that's what we determined due to my possible ovulation date and longer cycles. At 6 weeks I measured on the dot, but 12 weeks I was measuring a week ahead and I guess same again at this one.

After the scan was finished the maternal fetal medicine doctor came in to tell us everything looked perfect and they would be sending the images and notes over to my midwife. He questioned my dates and corrected me saying I was 20 weeks based on my scan and with my lmp. But my midwife hasn't changed my date.

I know 1 week doesn't change a thing, little miss will show up when she decides to come. But do I say I'm 20 weeks like the fetal medicine and scan said, or go by my original 19 weeks?

 

[DobbyForever]

I was always told to go by your earliest scan as they more they grow the less accurate because of different growth speeds. Did you confirm ovulation/is it possibly you ovulated a week earlier then you thought?

 

[Mrs Dragonfly]

I had a dotted crosshair on fertility friend so it's possible I could have ovulated on a different date My cycles have always been wacky. My 6 week scan I was measuring at 6 weeks, but my 12 week I was measuring 13 weeks.

 

[Mrs Dragonfly]

Actually looking at my temp chart back in August I had a lower temp 3 days and 8 days prior to when I got the dotted line, both marked with comments of ewcm so I suppose it's very possible!

 

[DobbyForever]

Ooo could be! If that's the case I would think 20 weeks for sure.

 

[Tui]

I was told that due dates aren't changed unless more than a week different, but they tend to go with earliest scan as its more accurate. Anatomy scans don't usually change anything date wise as they are to big for CRL. Averages are taken from head diameter, tummy, and leg length etc so your tech will be quoting averages. Maybe you are having a tall girl? Lol. I wouldn't worry about it regardless

 

[Mrs Dragonfly]

Maybe she is going to be tall! At my 12 week scan I thought she looked different than our first. Our first was round and squishy but this one is all legs

 

[Girly922]

My midwife said they will always take the date from the 12wk scan and disregard the LMP EDD. I'm not sure about the fetal medicine consultant though as we don't see ours until 28 weeks.

 

[Mrs Dragonfly]

Good to know, thank you Girly. I had always thought the 12 week scan was supposed to be the accurate one in determine size since at 6 weeks things are so small and hard to measure. I see my midwife again in a couple weeks so I'll just wait to ask.

 

[superfrizbee]

Go from the dates given by your 12 weeks scan. I know when I ovulate too but still ended up a week ahead on dates. I think I have babies that implant early, which can make quite a bit of difference as to dates.

 

[xdxxtx]

Yeah. There's no way your 12 or 20 week scans should figure conception date. At around 9 weeks, a fetus will form its own growth curve based on genetics and no longer follows the "average" all the time. 3 of my babies have all been "big" at my 20 week ultrasounds, one was smaller and was actually born the biggest.

 

[sil]

I was always told the first scan is most accurate as well. I measured a week ahead at 12 wks and 19 wks and my date is not changing.

 

[Girly922]

Yeah. There's no way your 12 or 20 week scans should figure conception date. At around 9 weeks, a fetus will form its own growth curve based on genetics and no longer follows the "average" all the time. 3 of my babies have all been "big" at my 20 week ultrasounds, one was smaller and was actually born the biggest.

Our first scan in the UK is at 12wks so that is the one they use for dating purposes.

 

[Mummafrog]

Yes from what I know the most accurate time to measure/date the pregnancy is between 11 and 14 weeks, so if you were put forward a week at the 12 week scan then I'd say that's what the doctor meant when he said you were 20 weeks now I would go from the date from the 12 week scan x

 

[Mrs Dragonfly]

Thanks ladies! For now I'll stick with that I'm at 19+6 and when I see my midwife again at 24 weeks I'll ask what's actually in my chart