Thursday, May 22, 2008

Numbers geek

The part of my brain that is good at math just likes to see the numbers sometimes...

The first set of percentiles are from the WHO charts, the second set is from the CDC charts and the third set is from an online calculator. I was just curious to see the difference based on a message board conversation I was part of the other day.

The way the numbers jump around point to my lack of trust in the length measurements, especially at the 9 month and 1 year appointments. Although I don't know that anyone could get an accurate measurement of a baby's length when they're being super squirmy!

It's interesting because I never got the impression until this past visit that Heather was anywhere near the 50th percentile for height, and yet it seems like she's spent more time close to the 50th than the 30th - unless you look at the online calculator. I also question the head circumference measurement at 9 months. I think that was the visit that we had a nurse in training...

When I plot her weight points on the CDC chart, I can clearly see the growth "slow down" predicted for breastfed babies as they get older. I'm sure I could do more with these numbers. But for now we'll just leave it as raw data. :-)

Birth
6 lb, 13 oz (3.1 kg) 35% 25% 27%
19.75" long (50.2 cm) 60% 60% 63%

1 month old
7 lb, 15 oz (3.6 kg) 15% 17.5% 6%
20.75" long (52.7 cm) 35% 40% 13%
13.8" HC (35 cm) 10% 8% 3%

2 months old
10 lb, 0 oz (4.5 kg) 15% 25% 14%
22 1/2" long (57.2 cm) 50% 55% 34%
14.6" HC (37 cm) 15% 10% 3%

4 months old
12 lb, 14 oz (5.8 kg) 20% 30% 22%
24" long (61 cm) 35% 45% 26%
15.7" HC (40 cm) 30% 25% 12%

6 months old
14 lb, 12 oz (6.7 kg) 25% 28% 18%
26" long (66 cm) 55% 60% 48%
16.3" HC (41.5 cm) 30% 20% 14%

9 months old
16 lb, 13 oz (7.6 kg) 25% 15% 12%
26 1/2" long (67.3 cm) 10% 20% 12%
16.5" HC (42 cm) 10% 8% 3%

1 year old
18 lb, 1 oz (8.2 kg) 25% 8% 6%
28" long (71.1 cm) 15% 20% 13%
17.3" HC (44 cm) 25% 20% 16%

15 months old
20 lb, 0 oz (9.1 kg) 30% 13% 8%
30.25" long (76.8 cm) 40% 45% 38%
17.7" HC (45 cm) 30% 25% 21%

1 comment:

Michelle said...

when I was doing fetal alcohol prevention research, we always had the head circumference taken three times because the variability even by the same nurse was very surprising. We also had to purchase a length board as well. We were working with newborns and they are also kind of hard to lay flat!

How does your practice do length? Mine varies from laying her on the scale that has length along the side to the very scientific draw a line on the paper by her head and feet and measure!

p.s. we love your number geekiness