Journal of Neonatology & Clinical Pediatrics Category: Clinical Type: Research Article
Continuously Tracking Growth of Preterm Infants from Birth to Two Years of Age
- William R Riddle^{1*}, Susan C DonLevy^{2}
- ^{1} Department Of Radiology And Radiological Sciences, Vanderbilt University, R-1311, Medical Center North, Nashville, TN, United States
- ^{2} Donlevy Consulting, Nashville, TN, United States
^{*}Corresponding Author:
William R RiddleDepartment Of Radiology And Radiological Sciences, Vanderbilt University, R-1311, Medical Center North, Nashville, TN, United States
Tel:+1 6153222432,
Fax:+1 6153223764
Email:bill.riddle@vanderbilt.edu
Received Date: Apr 02, 2015 Accepted Date: May 18, 2015 Published Date: Jun 01, 2015
Abstract
Keywords
ABBREVIATIONS
GA: Gestational Age HC: Head CircumferenceLEN: LengthLMP: Last Menstrual PeriodLMS: Three age specific cubic spline curves the L curve (Box-Cox power to remove skewness), the M curve (Median), and the S curve (coefficient of variation)NICU: Neonatal Intensive Care UnitSD: Standard DeviationU: Mean WHO: World Health Organization
INTRODUCTION
While there have been many published growth charts for premature infants, none of these has been embraced as a universal standard. One of the greatest problems in constructing intrauterine growth curves is the determination of gestational age [7]. Most intrauterine growth curves were developed prior to the routine use of ultrasound scanning. For these studies, gestational age was estimated solely by the mother’s reported Last Menstrual Period (LMP), which may be biased due to erroneous recall by the mother or early bleeding in the pregnancy [8]. Since the 1980s, prenatal ultrasounds are often utilized to provide more precise estimates of gestational age. Nine studies from the United States, Australia, Italy, Israel, Turkey, Sweden and the United Kingdom with gender-specific percentiles for birth weight, head circumference, and length were compared. If some of these studies are statistically identical, we propose that the values can be used as a standard. The objective of this study is to provide gender-specific premature infant growth curves that can be incorporated with the 2006 WHO growth standards to continously track weight, head circumference, and length from 22 weeks of gestion through 2 years of age.
MATERIALS AND METHODS
Percentiles from Thomas (USA)
Percentiles from Dobbins (Australia)
Percentiles from Bertino (Italy)
Percentiles from Davidson (Israel)
Percentiles from Kurtoglu (Turkey)
Percentiles from Niklasson (Sweden)
Percentiles from Cole (UK)
Percentiles from Olsen (USA)
Vanderbilt NICU percentiles (USA)
To summarize and smooth the data, several mathematical models were evaluated: exponential [y = a exp (b x)], power [y = a x^{b}], linear [y = a x + b], quadratic [y = a x^{2} + b x + c], and cubic [y = a x^{3} + b x^{2} + c x + d]. An exponential function analysis fits a linear function to semi-logarithmic data (logarithm Y axis) and a power function analysis fits a linear function to full-logarithmic data (logarithm X and Y axes). The mathematical models were evaluated with SAS statistical software (Cary, NC) to determine the best model based on the Akaike’s information criterion [19] and the Bayesian information criterion [20].
The exponential function, which describes uninhibited growth with a constant growth velocity, was the best model for birth weight. The percentiles for birth weight (in grams) were described with the following function:
(1)where variable GA is gestational age in weeks, constant A has units of grams, and constant B is the growth velocity for weight in units of g/kg/day. Power functions best described head circumference and length. When the power functions for the 50^{th} percentile of HC and LEN were compared to the linear functions with zero intercept, the largest difference between the two models was 1 mm. The simpler linear model with zero intercept was selected to describe HC and LEN and the percentiles (in cm) were described by the following functions:
(2)
(3)where variable GA is gestational age in weeks, constant C is the growth velocity for head circumference in cm/week, and constant D is the growth velocity for length in cm/week. Using these models, best-fit equations for the 5^{th}, 10^{th}, 25^{th}, 50^{th}, 75^{th}, 90^{th} and 95^{th} percentiles for birth weight, head circumference, and length were generated with PSI-Plot (Poly Software Incorporated, Pearl River, NY).
The LMS method is used to construct growth charts [21]. It estimates the percentiles in terms of three age specific cubic spline curves: the L curve (Box-Cox power to remove skewness), the M curve (Median), and the S curve (coefficient of variation). The gender-specific LMS coefficients for birth weight, head circumference, and length were determined with LMS chartmaker light version 2.54 (http://www.healthforallchildren.com/?product=lmschartmaker-light). The degrees of freedom for the fitted LMS spline curves were, respectively, 2, 6 and 4 for weight and 0, 4 and 3 for length and head circumference.
Longitudinal data from a premature infant
Combined intrauterine and WHO growth curves
Birth percentile growth trajectories
Comparing premature percentiles
RESULTS
Data from Vanderbilt NICU
Figure 1: Comparison between the 5^{th}, 50^{th} and 95^{th} percentiles for male birth weight from the Vanderbilt NICU using equation 1 and the LMS method.
GA (wks) | N | mean | SD | Percentiles | ||||||
5^{th} | 10^{th} | 25^{th} | 50^{th} | 75^{th} | 90^{th} | 95^{th} | ||||
Weight (g) | ||||||||||
22 | 6 | 568 | 50 | 556 | ||||||
23 | 22 | 610 | 81 | 551 | 600 | 654 | ||||
24 | 83 | 676 | 95 | 505 | 561 | 619 | 680 | 732 | 790 | 810 |
25 | 85 | 736 | 116 | 531 | 590 | 670 | 756 | 820 | 848 | 870 |
26 | 120 | 833 | 122 | 630 | 688 | 765 | 842 | 903 | 991 | 1041 |
27 | 146 | 968 | 181 | 655 | 740 | 861 | 970 | 1067 | 1199 | 1260 |
28 | 180 | 1047 | 203 | 719 | 769 | 910 | 1040 | 1177 | 1301 | 1389 |
29 | 197 | 1219 | 249 | 828 | 944 | 1041 | 1230 | 1369 | 1472 | 1636 |
30 | 237 | 1389 | 278 | 939 | 1056 | 1220 | 1390 | 1557 | 1712 | 1781 |
31 | 276 | 1605 | 315 | 1068 | 1205 | 1432 | 1608 | 1792 | 1977 | 2116 |
32 | 457 | 1748 | 320 | 1197 | 1348 | 1550 | 1743 | 1950 | 2124 | 2273 |
33 | 463 | 1949 | 381 | 1331 | 1510 | 1735 | 1950 | 2126 | 2394 | 2563 |
34 | 505 | 2186 | 447 | 1502 | 1661 | 1889 | 2170 | 2455 | 2699 | 2911 |
35 | 455 | 2464 | 484 | 1676 | 1843 | 2150 | 2459 | 2750 | 3070 | 3292 |
36 | 482 | 2689 | 469 | 1956 | 2100 | 2400 | 2685 | 2979 | 3269 | 3469 |
Total: | 3714 | |||||||||
HC (cm) | ||||||||||
22 | 4 | 21.3 | 21.3 | |||||||
23 | 13 | 21.2 | 1.6 | 20.0 | 21.0 | 22.0 | ||||
24 | 63 | 22.3 | 1.7 | 20.0 | 20.5 | 22.0 | 22.0 | 23.0 | 23.0 | 24.0 |
25 | 78 | 22.9 | 1.3 | 21.0 | 21.0 | 22.0 | 23.0 | 23.7 | 24.0 | 25.0 |
26 | 112 | 24.2 | 1.6 | 22.0 | 23.0 | 23.0 | 24.0 | 25.0 | 26.0 | 26.7 |
27 | 133 | 25.3 | 1.7 | 22.5 | 23.0 | 24.0 | 25.0 | 26.0 | 27.0 | 28.0 |
28 | 163 | 25.9 | 1.7 | 23.0 | 24.0 | 25.0 | 26.0 | 27.0 | 28.0 | 28.0 |
29 | 188 | 27.0 | 1.6 | 24.5 | 25.0 | 26.0 | 27.0 | 28.0 | 29.0 | 30.0 |
30 | 216 | 28.1 | 1.9 | 25.4 | 26.0 | 27.0 | 28.0 | 29.0 | 30.0 | 31.0 |
31 | 259 | 29.1 | 1.8 | 26.0 | 27.0 | 28.0 | 29.0 | 30.0 | 31.0 | 32.0 |
32 | 418 | 29.9 | 1.7 | 27.0 | 28.0 | 29.0 | 30.0 | 31.0 | 32.0 | 32.0 |
33 | 419 | 30.6 | 1.8 | 28.0 | 28.7 | 29.9 | 31.0 | 31.9 | 33.0 | 33.0 |
34 | 442 | 31.6 | 1.8 | 29.0 | 29.5 | 30.0 | 32.0 | 33.0 | 34.0 | 34.5 |
35 | 409 | 32.6 | 1.9 | 30.0 | 30.5 | 31.5 | 33.0 | 33.7 | 35.0 | 35.0 |
36 | 420 | 33.4 | 2.0 | 30.0 | 31.0 | 32.0 | 33.5 | 34.5 | 35.0 | 36.0 |
Total: | 3337 | |||||||||
LEN (cm) | ||||||||||
22 | 4 | 30.8 | 30.8 | |||||||
23 | 13 | 30.6 | 2.3 | 30.0 | 31.0 | 31.0 | ||||
24 | 61 | 32.4 | 2.6 | 28.0 | 29.0 | 31.0 | 32.0 | 33.5 | 35.5 | 37.0 |
25 | 76 | 33.2 | 2.0 | 30.0 | 31.0 | 32.0 | 33.0 | 34.0 | 36.0 | 36.0 |
26 | 105 | 34.5 | 1.8 | 31.0 | 32.0 | 33.0 | 35.0 | 36.0 | 36.0 | 37.0 |
27 | 131 | 35.8 | 2.6 | 31.0 | 32.0 | 34.0 | 36.0 | 38.0 | 39.0 | 39.3 |
28 | 158 | 36.9 | 2.1 | 33.0 | 34.0 | 35.5 | 37.0 | 38.0 | 39.0 | 40.0 |
29 | 186 | 38.5 | 2.6 | 34.0 | 35.0 | 37.0 | 38.5 | 40.0 | 42.0 | 42.0 |
30 | 213 | 40.1 | 2.4 | 36.3 | 37.0 | 38.5 | 40.0 | 42.0 | 43.0 | 44.0 |
31 | 261 | 41.7 | 2.9 | 37.0 | 38.0 | 40.0 | 42.0 | 43.5 | 45.0 | 46.0 |
32 | 414 | 42.9 | 2.9 | 38.0 | 40.0 | 41.0 | 43.0 | 45.0 | 46.0 | 47.0 |
33 | 411 | 44.0 | 2.7 | 39.0 | 41.0 | 42.5 | 44.0 | 46.0 | 47.0 | 48.0 |
34 | 444 | 45.4 | 3.1 | 40.0 | 42.0 | 43.9 | 46.0 | 47.0 | 49.0 | 50.0 |
35 | 404 | 46.9 | 3.2 | 41.2 | 43.0 | 45.0 | 47.0 | 49.0 | 50.0 | 51.0 |
36 | 409 | 48.0 | 2.8 | 43.0 | 44.0 | 46.0 | 48.0 | 50.0 | 51.5 | 52.0 |
Total: | 3290 |
GA (wks) | N | mean | SD | Percentiles | ||||||
5^{th} | 10^{th} | 25^{th} | 50^{th} | 75^{th} | 90^{th} | 95^{th} | ||||
Weight (g) | ||||||||||
22 | 7 | 521 | 103 | 454 | ||||||
23 | 24 | 589 | 69 | 538 | 592 | 642 | ||||
24 | 68 | 642 | 91 | 504 | 540 | 579 | 643 | 697 | 761 | 796 |
25 | 87 | 701 | 105 | 520 | 561 | 635 | 705 | 770 | 842 | 859 |
26 | 102 | 805 | 154 | 622 | 651 | 705 | 780 | 876 | 1006 | 1097 |
27 | 139 | 918 | 218 | 625 | 668 | 778 | 905 | 1025 | 1194 | 1260 |
28 | 180 | 1047 | 203 | 719 | 769 | 910 | 1040 | 1177 | 1301 | 1389 |
29 | 197 | 1219 | 249 | 828 | 944 | 1041 | 1230 | 1369 | 1472 | 1636 |
30 | 237 | 1389 | 278 | 939 | 1040 | 1150 | 1360 | 1497 | 1659 | 1741 |
31 | 263 | 1493 | 342 | 959 | 1084 | 1272 | 1492 | 1695 | 1863 | 2020 |
32 | 410 | 1673 | 338 | 1185 | 1304 | 1471 | 1655 | 1851 | 2049 | 2191 |
33 | 364 | 1880 | 368 | 1335 | 1450 | 1639 | 1880 | 2092 | 2331 | 2521 |
34 | 388 | 2077 | 412 | 1450 | 1579 | 1834 | 2041 | 2278 | 2536 | 2768 |
35 | 302 | 2274 | 479 | 1505 | 1720 | 1960 | 2227 | 2557 | 2862 | 3152 |
36 | 310 | 2588 | 561 | 1791 | 1915 | 2218 | 2551 | 2906 | 3301 | 3555 |
Total: | 3073 | |||||||||
HC (cm) | ||||||||||
22 | 3 | 20.7 | 20.0 | |||||||
23 | 16 | 22.4 | 2.3 | 21.4 | 22.0 | 22.6 | ||||
24 | 58 | 22.0 | 1.1 | 20.0 | 21.0 | 21.0 | 22.0 | 23.0 | 23.0 | 23.2 |
25 | 74 | 23.1 | 2.2 | 21.0 | 21.0 | 22.0 | 23.0 | 23.5 | 25.0 | 27.1 |
26 | 98 | 23.7 | 1.6 | 21.9 | 22.0 | 23.0 | 23.5 | 24.5 | 25.5 | 26.0 |
27 | 126 | 24.7 | 1.6 | 22.4 | 23.0 | 23.6 | 24.5 | 25.5 | 27.0 | 27.4 |
28 | 156 | 25.6 | 1.6 | 23.0 | 23.5 | 25.0 | 25.8 | 27.0 | 28.0 | 28.0 |
29 | 200 | 26.7 | 1.6 | 24.0 | 24.5 | 25.7 | 27.0 | 27.5 | 29.0 | 29.0 |
30 | 217 | 27.8 | 2.2 | 25.0 | 26.0 | 27.0 | 28.0 | 29.0 | 30.0 | 30.1 |
31 | 252 | 28.5 | 1.9 | 25.6 | 26.0 | 27.0 | 29.0 | 30.0 | 31.0 | 31.0 |
32 | 369 | 29.2 | 1.7 | 26.5 | 27.0 | 28.0 | 29.0 | 30.0 | 31.0 | 32.0 |
33 | 330 | 30.2 | 2.0 | 27.0 | 28.0 | 29.0 | 30.1 | 31.0 | 32.5 | 33.0 |
34 | 347 | 31.1 | 2.1 | 28.0 | 29.0 | 30.0 | 31.0 | 32.0 | 33.0 | 34.0 |
35 | 264 | 31.8 | 2.1 | 28.6 | 30.0 | 31.0 | 32.0 | 33.0 | 34.0 | 35.0 |
36 | 262 | 32.8 | 2.2 | 29.5 | 30.0 | 31.5 | 33.0 | 34.0 | 35.0 | 36.0 |
Total: | 2772 | |||||||||
LEN (cm) | ||||||||||
22 | 3 | 28.3 | 28.0 | |||||||
23 | 15 | 31.6 | 2.0 | 30.0 | 31.0 | 32.0 | ||||
24 | 54 | 32.0 | 2.8 | 29.7 | 30.5 | 32.0 | 33.0 | 34.4 | 35.2 | |
25 | 72 | 32.9 | 2.9 | 28.8 | 29.1 | 31.0 | 33.0 | 34.0 | 36.0 | 36.2 |
26 | 92 | 33.8 | 2.4 | 30.0 | 31.0 | 32.0 | 34.0 | 35.0 | 36.5 | 38.0 |
27 | 125 | 35.3 | 2.5 | 32.0 | 32.5 | 34.0 | 35.0 | 36.5 | 38.3 | 39.0 |
28 | 153 | 36.6 | 2.2 | 33.0 | 33.1 | 35.5 | 37.0 | 38.0 | 39.0 | 40.0 |
29 | 194 | 38.3 | 3.0 | 32.8 | 34.7 | 37.0 | 38.0 | 40.0 | 42.0 | 42.4 |
30 | 210 | 39.9 | 2.5 | 36.0 | 37.0 | 38.0 | 40.0 | 41.0 | 43.0 | 44.0 |
31 | 247 | 41.0 | 2.9 | 36.0 | 37.0 | 39.0 | 41.0 | 43.0 | 44.7 | 45.4 |
32 | 373 | 42.1 | 2.8 | 38.0 | 39.0 | 40.5 | 42.0 | 44.0 | 45.5 | 46.0 |
33 | 326 | 43.7 | 2.9 | 39.0 | 40.0 | 42.0 | 44.0 | 46.0 | 47.0 | 48.0 |
34 | 342 | 44.8 | 2.9 | 40.0 | 41.0 | 43.0 | 45.0 | 47.0 | 48.5 | 49.0 |
35 | 264 | 45.8 | 3.3 | 41.0 | 42.0 | 43.5 | 46.0 | 48.0 | 50.0 | 51.0 |
36 | 260 | 47.4 | 3.0 | 42.0 | 43.5 | 45.5 | 47.8 | 49.0 | 51.0 | 52.0 |
Total: | 2730 |
Percentile | A (g) | B (g/kg/day) | C (cm/week) | D (cm/week) |
Female constants | ||||
5^{th} | 34.32 | 15.64 | 0.8259 | 1.1715 |
10^{th} | 34.32 | 16.03 | 0.8484 | 1.2043 |
25^{th} | 38.02 | 16.2 | 0.8834 | 1.2629 |
50^{th} | 36.53 | 16.98 | 0.9192 | 1.3213 |
75^{th} | 40.87 | 16.98 | 0.9499 | 1.3720 |
90^{th} | 43.71 | 17.18 | 0.9838 | 1.4250 |
95^{th} | 41.90 | 17.69 | 1.0037 | 1.4513 |
Male constants | ||||
5^{th} | 31.07 | 16.29 | 0.8423 | 1.1835 |
10^{th} | 35.15 | 16.21 | 0.8651 | 1.2264 |
25^{th} | 38.41 | 16.43 | 0.8948 | 1.2819 |
50^{th} | 40.56 | 16.75 | 0.9333 | 1.3381 |
75^{th} | 41.49 | 17.12 | 0.9636 | 1.3885 |
90^{th} | 41.86 | 17.52 | 0.9927 | 1.4332 |
95^{th} | 40.54 | 17.95 | 1.0129 | 1.4592 |
DISCUSSION
The 50^{th} percentiles for weight from Niklasson [15] (Sweden), Cole [17] (UK), and Olsen [18] (USA) are parallel to the percentiles from Vanderbilt, Thomas [9] (USA), Davidson [8] (Israel), and Kurtoglu [14] (Turkey). This means these infants have the same growth velocity with systematically higher birth weights, systematic errors in estimating gestational age, and/or different exclusion criteria. Niklasson’s 50^{th} percentiles for females were 21% greater and males were 11% greater than the percentiles from Vanderbilt, Thomas [9] (USA), Davidson [8] (Israel), and Kurtoglu [14] (Turkey). Cole’s 50^{th} percentiles for females were 9% greater and males 4% greater than the percentiles from Vanderbilt, Thomas [9] (USA), Davidson [8] (Israel), and Kurtoglu [14] (Turkey). Olsen’s 50^{th} percentiles for males and females were 4% greater than the percentiles from Vanderbilt, Thomas [9] (USA), Davidson [8] (Israel) and Kurtoglu [14] (Turkey).
The differences between the 50^{th} percentiles for birth weight of males and females from the nine studies showed five studies, Vanderbilt, Thomas, Davidson, Cole and Olsen, in the 5.6% to 6.7% range. Kurtoglu had 2.7% difference and Bertino had 14.3% difference. Niklasson had statistically identical male and female growth curves. This could be due to estimating gestational age solely on ultrasound estimation.
The Vanderbilt male and female 10^{th}, 50^{th} and 90^{th} percentiles for head circumference are identical with percentiles from Olsen [18] (USA). This means that equation 2 can be used to describe the head circumference of the premature infants in both of these studies. Differences from the other studies could be explained by different exclusion criteria, by small numbers, and/or by different methods for determining gestational age.
The Vanderbilt male and female 10^{th}, 50^{th} and 90^{th} percentiles for length are identical with the percentiles from Bertino [13] (Italy), Davidson [8] (Israel) and Olsen [18] (USA). This means that equation 3 can be used to describe the length of the premature infants in all these studies. Differences from the other studies could be explained by different exclusion criteria, by small numbers, and/or by different methods for determining gestational age.
In summary, the intrauterine curves (equations 1, 2, and 3) can be used to describe premature infants from different countries. Growth trajectories for weight, head circumference, and length based on birth percentiles provide insights for the growth for each infant. The combined intrauterine and WHO growth curves depict the growth continium of the prematurely born infant from a gestational age of 22 weeks to 2 years of age. These gender-specific curves are suitable for individualized spreadsheets and electronic medical record applications.
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Citation:Riddle WR, DonLevy SC (2015) Continuously Tracking Growth of Preterm Infants from Birth to Two Years of Age. J Neonatol Clin Pediatr 2: 011.
Copyright: © 2015 William R Riddle, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Weight for Age Curve | HC for Age Curve | Length for Age Curve | |||||||||
L Curve | M Curve | S Curve | L Curve | M Curve | S Curve | L Curve | M Curve | S Curve | |||
GA | Value | Value | Value | Value | Value | Value | Value | Value | Value | ||
Female Curves | |||||||||||
22 | 0.36140 | 518.91 | 0.12525 | 1 | 20.577 | 0.07864 | 1 | 29.385 | 0.08283 | ||
23 | 0.34310 | 576.51 | 0.13963 | 1 | 21.383 | 0.07675 | 1 | 30.561 | 0.08077 | ||
24 | 0.32477 | 635.57 | 0.15468 | 1 | 22.194 | 0.07488 | 1 | 31.736 | 0.07870 | ||
25 | 0.30638 | 704.16 | 0.17041 | 1 | 23.023 | 0.07307 | 1 | 32.923 | 0.07662 | ||
26 | 0.28792 | 791.20 | 0.18583 | 1 | 23.882 | 0.07134 | 1 | 34.150 | 0.07459 | ||
27 | 0.26937 | 895.43 | 0.19877 | 1 | 24.780 | 0.06981 | 1 | 35.443 | 0.07277 | ||
28 | 0.25063 | 1,017.57 | 0.20741 | 1 | 25.709 | 0.06860 | 1 | 36.801 | 0.07126 | ||
29 | 0.23167 | 1,161.39 | 0.21229 | 1 | 26.650 | 0.06774 | 1 | 38.199 | 0.07009 | ||
30 | 0.21279 | 1,316.41 | 0.21377 | 1 | 27.570 | 0.06705 | 1 | 39.590 | 0.06913 | ||
31 | 0.19437 | 1,477.30 | 0.21198 | 1 | 28.448 | 0.06632 | 1 | 40.937 | 0.06840 | ||
32 | 0.17595 | 1,651.39 | 0.20793 | 1 | 29.302 | 0.06571 | 1 | 42.245 | 0.06783 | ||
33 | 0.15709 | 1,841.61 | 0.20432 | 1 | 30.163 | 0.06545 | 1 | 43.530 | 0.06737 | ||
34 | 0.13778 | 2,045.89 | 0.20322 | 1 | 31.026 | 0.06543 | 1 | 44.784 | 0.06696 | ||
35 | 0.11825 | 2,264.15 | 0.20505 | 1 | 31.889 | 0.06555 | 1 | 46.024 | 0.06655 | ||
36 | 0.09862 | 2,493.75 | 0.20834 | 1 | 32.755 | 0.06575 | 1 | 47.271 | 0.06603 | ||
22 | 1.01841 | 552.61 | 0.11408 | 1 | 20.359 | 0.07056 | 1 | 29.676 | 0.06818 | ||
23 |