When is small for dates a concern?

[Plummeting]

I just had an anatomy scan today, at what was 21wk3d by LMP, but I didn't track ovulation or anything. I DO have extremely, extremely regular periods at 27 to 28 days, and am never late. I know that with my 2nd dd, I conceived 8 or 9 days before my period was due (I know that's unusual, but it happened), so it's possible I have a short luteal phase normally, which would mean it would be normal for my due date to be a few days behind when they think it should be. So anyway, they said I should be 21wk3 days based on my LMP, but that overall, the baby was measuring 19wk6d. They adjusted my due date by 8 days based on that, which is not the 11 days they said I was off, so I have no idea how this works, lol.

Of all the measurements they took, nothing was outside the margin of error. So for instance, something like 19wk5d +/-14 days. If it could be plus or minus 14 days, then I'm good, since I'm somewhere around 21wk3d. The arm, leg, and head measurements were all somewhere in the 19 week range. The abdominal measurement was actually 21wk6d, so it's not small all over - apparently just short and fat with a small head circumference. The weight they were guessing was 12 ounces (I know they can be off by a LOT, but this is what they're basing everything on, so this is what I'm sharing). Online I've read everything from 10.58 ounces to 13.9 ounces is the average weight for a 21 week fetus, so I have no idea what's accurate.

They want me to come back in 4 weeks to check to see that the baby is growing. I think everything is fine, but would like some reassurance. Am I likely wrong or likely right? They said the baby looked fine in every way, just small. For reference, my two daughters were born at 38wk1d, at 6lbs10oz, 19"long and 39wk5d at 8lb0oz, 20.25" long.

[mamaforever]

Hi Plummeting, I don't have a lot of knowledge about this but I'm pretty sure that everything is fine.  You must be really scared though and I'm sorry you're going through this!  I think when you get into the second trimester, the babies start growing at different rates and can be bigger or smaller than the average and be perfectly fine.  My DS at my 18 week scan measured to be 19.5 weeks, so was bigger than average by 1.5 weeks.  They thought about changing my due date, but I was absolutely certain when I conceived.  He measured big throughout the rest of the pregnancy and was 8 lbs 4 oz at 39 weeks when he was born.  You're right that the scans are not absolutely accurate so they could definitely be off by the size and weight too.

I'm sorry if my post is not helpful - but I really think all is okay with your LO.  Hugs.

[Plummeting]

To tell the truth, I'm really not scared. I'm annoyed because I think they're freaking out over absolutely nothing. When I went in for my first visit, I said my LMP was either 8/21 or 8/22, and I wasn't sure which. The nurse panicked and said I absolutely must have a dating ultrasound, to be sure, which is absurd. One day is irrelevant, but she insisted I choose a date. I said, "Fine. The 21st." If I had told her the 22nd, then they would have sent me on my merry way yesterday, assured that all was well. They told me that their cutoff was 10 days difference between the u/s and my dates by LMP. I missed it by ONE day. I think they're being ridiculous and I'm just curious if other people agree, or if I'm being cavalier. Any time someone tells you something might be wrong, there's always that nagging doubt, so of course I have that right now, but mainly I'm just aggravated.

Oh, I forgot to say that I'm only 5'0" tall, so if I had another small baby, that really shouldn't be a shocker. One was average, one was small. Seems realistic to expect someone my size might have a short baby. And they don't actually measure head circumference, but the length from side to side. If the baby has a narrow head, as do my husband and both of my daughters, then it would measure small. That's sort of to be expected. So the whole thing just seems weird to be freaking out about. How anyone could look at me and think I should NOT have a short baby is beyond me, lol. Sounds like it'll be between DD1, who was small all over, and DD2, who was right at average length, but 8 ounces over average weight - so short and fat.

[mamaforever]

I definitely agree with you, and I'm glad you're not freaking out about it.  That's ridiculous that they stressed about the LMP so much, and it doesn't even mean anything because ovulation day can be so different for different women.  I really think all is fine and I hope others reply too to give you some more reassurance.

[Plummeting]

Thank you! It's good to know that at least one other person can see why I think they're overreacting. I know a lot of my friends are quite sure I should be in full on panic mode right now. lol

[norskelove]

Given your size and your history of luteal phases likely on the shorter end, I would not be concerned.   Did you have a dating ultrasound early in the pregnancy?  Those are much more accurate when it comes to determining a due date.  My DD1 measured small at her 20 week u/s, but was measuring exactly on track for her 8 week u/s......so nobody batted an eye.   My OB told me she will not change a due date based on the 20 week u/s, but she will change a due date if the baby is more than a week ahead or behind on the first trimester u/s.  

[Plummeting]

I didn't do an early ultrasound. I know there were 3 days in one week that we DTD over the weekend, but no other days after that for a couple of weeks, and I think I ovulated on about day 18 or 19 of my cycle. I wasn't tracking, so I can't be sure. I just know I have about 12 hours worth of ovulation pain every month, and I had that sort of pain a few days after we DTD, then I kind of had an "Oh, I wonder if I'm going to get pregnant now," thought, and even talked to DH about it, so I know it wasn't on day 14. I know when I did get pregnant with dd2, which is my only clue as to having a short luteal phase since I never paid attention to when I ovulated, other than noticing I was in pain. So I think it's very likely that I ovulated a few days after when they think I did, I just don't want to say that for sure because I'm solely going on what I assume to be ovulation pain.

I never knew I would ever put this much thought into trying to guess when I ovulated. lol I guess the point is that I could've had an LMP a day later than they have officially recorded, and ovulated 4 days "late" based on that, which would put me within 6 days of their measurements. That seems reasonable.