How do they measure...?

CrazyMary77 · December 2012

Last week I had an u/s at 24w5d and they said that our baby is measuring 25w6d. They also told us that our baby is in the 65th percentile for size. After I left I starting wondering if the baby is measuring a week ahead just because she is slightly larger than average? Anyone know how do they measure how far along the baby is? They said that the size is measured by the length of the arm and leg bones, but is that what they also use to determine that she's 25w6d? I'm going to ask my OB when I see her on Monday (I got the u/s done at the office where we had our genetic screening, not the OB's office), but was curious if anyone knows.

old_time_girl · December 2012

Ya know, i have no clue. Interesting question. You'll have to let me know when you find out.
This LO was 3 days ahead, but it sounded to me like they were basing that off of babys weight, which they mentioned was just slightly above average. They didn't give me the percentiles though.

jackie9480 · December 2012

That is a good question. I will be interested to hear what you find out too! I have measured a week ahead at both 20 & 24 wks. They said measurments are in the 90% percentile. I was confused by mine after I had gotten home and thought about it more.

skoogirl · December 2012

I think they measure head to rump.

finallyplanned · December 2012

Sorry, I'm no help either but when I had my ultrasound, the measurements came back with a due date of March 29th but the doctor gave me a due date of April 6th using the first day of the last period.

I do know that my OB explained to me early in my pregnancy that the first trimester basically every baby grows and develops at the same rate. Once we get into the second and third trimester, there are many different factors that play into the size of the baby such as geographical location, diet, mothers size, genetics, etc. So, a person on one side of the country at 25w5days could have a baby that is 10% larger(or smaller) than someone on the other side of the country at the same gestation.

I'm not too worried about any of that, I figure this baby is coming when she is ready whether its 10 days before or after the EDD. I've given myself a 1 month window, 2 weeks either way, to expect her arrival. All we can do is hope for the best and be prepared when it is time.

lexyraejay · December 2012

The percentile is how the arm and leg measurements compare to the average measurements for babies at that stage of development. So, if you're 20 weeks exactly, but your baby measures above the 50th percentile, then they'll probably tell you the baby is measuring more than 20 weeks - what ever week & day matches the percentile of the baby's arm & leg measurements.

Ooglybear · December 2012

I think (emphasis on "think") that the measurement means the average fetus at 25w6d has those measurements. At this stage, baby's development was vary from average quite a big, so even though your LO is 24w5d gestation, s/he is measuring on the largish side.

I believe the main measurements are arm and leg bones, like you said, but they take all the measurements into consideration.

Zelda925 · December 2012

My doc said go by your LMP.... as growth will vary because I measured 3 days early at 50 % and I asked him if it meant anything (i.e. did my due date change?) and he said no.

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