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. 2018 May 15;8:7567. doi: 10.1038/s41598-018-25744-7

New birthweight percentiles by sex and gestational age in Southern China and its comparison with the INTERGROWTH-21st Standard

Fei Yao 1,#, Huazhang Miao 1,#, Bing Li 1,#, Yuntao Wu 1, Qingguo Zhao 2,✉
PMCID: PMC5954150  PMID: 29765081

Abstract

We first showed the sex- and gestational age (week)-specific birthweight distributions from primiparous and multiparous mothers. Birthweight percentiles were created by using the Lambda Mu Sigma (LMS) method. We established the birthweight percentiles in Southern China and provide clinicians and researchers with up-to-date population norms of birthweight percentiles. Then we use the data from Birth Certificate System between Jan 1st, 2017 and Oct 31st, 2017, which included 1,245,364 live births to calculate SGA and LGA ratio by these three birthweight references- the new INTERGROWTH-21st standard, China’s 2015 research standard and our birthweight percentiles. The overall prevalence of SGA estimated by our standards, the China’s 2015 research standards and INTERGROWTH-21st standards, were 10.21%, 12.93% and 7.98%, respectively, whereas the overall prevalence of LGA was 9.88%, 4.48% and 8.37%, respectively.

Introduction

Neonatal birthweight has been an important indicator of common concern in obstetrics and neonatology. This factor is critical for the study of adverse pregnancy outcomes and the prediction of neonatal mortality and morbidity. Extreme (large or small) neonatal birthweight increase the risks of diseases in adulthood1,2. The birthweight percentile is used to monitor the clinical measurement within the population value of the individual within the range. Infants who are SGA or LGA, are commonly defined as below the 10th or above the 90th centiles according to the birthweight percentile reference standard3,4. Brazil, India, Korea, Canada, United States, Japan, and Australia have published studies for assessing birthweight for gestational age (week)5–11. Nowadays, INTERGROWTH-21st reported a new global newborn birthweight standard, and attempted to define an international birthweight standard in the context of optimal maternal health and fetal growth12.

In our analysis, we first showed the sex- and gestational age (week)–specific birthweight distributions for primiparous and multiparous mothers separately. Using the birth certificate data in 2017, the SGA ratio and the LGA ratio obtained through the standards’ 10th and 90th percentile values. Standards included the new INTERGROWTH-21st standard and China’s 2015 research standard then we compare the ratios. In China, the Chinese newborn collaboration network also produced a newborn birthweight standard in 201513. Since birthweight may differ by race and ethnicity, and there have been increasing number of older and multiparous mothers after the general implementation of two-child policy in China since 2016, the birthweight standard may change and the outdated classification of infants as SGA or LGA may not be accurately defined. This paper is to establish our birthweight standard in Guangdong province in Southern China and study up-to-date birthweight changes and abnormal birthweight risk factors.

Materials and Methods

All birth data were obtained from the Guangdong Provincial Birth Certificate System, about 1900 medical institutions, which collected all information about infants who were admitted to medical institutions accredited to midwifery in Guangdong Province. After the birth, maternity medical workers would bare the baby on the electronic scales, read the stable weight data, weighing accuracy is 1 g; on the other hand, health care attendants or midwives would fill in the newborns’ delivery information in the regional maternal and child information system. The system setting logic was corrected to ensure the correct range. At last, regional maternal and child information would upload to Guangdong Provincial Birth Certificate System. The Chief of Midwifes and the Chief of Physicians in hospitals confirmed the information after data entry. Before the birth certificate is issued, the Department of Medical Administration and parents also confirmed the birth information. All the information was verified by the medical professional. The birth registry database maintains the date of birth, gestational age (week) at birth, birthweight, infant sex, parents’ ages, registered residence and parity. We included the babies in the study which were born except for stillbirth, death within seven days, and birth defects. Our analyses were based on 5,516,173 births after exclusions. The study was reviewed and approved by Ethics Committee of Guangdong Women and Children Hospital.

The raw data of all newborns (1,771,534 in 2014, 1,627,254 in 2015, and 1,757,385 in 2016) were analyzed. The gestational age (week) was measured combining with mother-reported last menstrual period, early pregnancy ultrasound, and postnatal gestational age (week) assessment. It was expressed in completed weeks. The birthweight was measured immediately after the delivery with measurement accurate to 1 gram. Birthweight percentiles were created by using the Lambda Mu Sigma (LMS) method, which can be fitted within the GAMLSS package by assuming that the birthweight has a Box-Cox Cole and Green (BCCG) distribution14,15. The smoothed data were represented by the BW percentile curves. The curves appeared at intervals of one week by gestation and separated into all single births. We also constructed separate curves and tables for male and female newborns for the 3rd, 5th, 10th, 25th, 50th, 75th, 90th, 95th, and 97th percentiles from 25 to 42 completed weeks based on smoothed estimated curves. The charts and tables were stratified by gender and parity for the 3rd, 5th, 10th, 50th, 90th, 95th and 97th percentiles, and SD were obtained after smoothing. SGA was defined as weight below the 10th percentile of a sex- and gestational age (week)–specific birthweight curve.

Then we use the data from Birth Certificate System between Jan 1st, 2017 and Oct 31st, 2017, which included 1,245,364 live births to calculate SGA and LGA ratio by three birthweight references. The 10th percentile values of the above three birthweight references were compared against each other, and the difference in cutoff weight at each gestational age (week) was calculated. The same comparison was performed for the 90th percentile values. The GAMLSS package (version 5.0.6) for R statistical software (version 3.4.2) was used for the analysis.

Results

A retrospective survey for data pertaining to birthweight, maternal parity and infant gender was conducted on 5,516,173 singleton live births at gestational age (week)s 25–42 weeks from January 1st, 2014 to December 31st, 2016.We included the babies in the study which were born except for stillbirth, death within seven days, and birth defects. After exclusion of birthweight outliers, we included 5,516,173 single neonates in the analysis, comprising 710,480 firstborn boys, 649,882 firstborn girls, 2,053,993 later-born boys, and 1,741,818 later-born girls. Males comprised 53.61% of the births, and 25.70% of infants were firstborn. Late premature infants born at 34–36 weeks’ gestation and premature infants born at <34 weeks’ gestation accounted for 3.64% and 0.78% of the total infant population, respectively. 20 to 34 years-old mothers accounted for 84.10% of all pregnant women, among which 8.90% were above 35 years-old, and was 18.20% of fathers were older than 35 years-old. Vaginal delivery and cesarean section delivery accounted for 72.10% and 27.70% respectively, while the remaining delivery modes were unclear.

The percentile charts (3rd, 5th, 10th, 50th, 90th, 95th and 97th centiles) were stratified by sex and mother’s parity. First of all, we showed smoothed percentiles for birthweight by gestational age (week) for male and female babies in Table 1. Then all infants from the primiparous mothers were grouped based on gestational age (week), and the data at the 3rd, 5th, 10th, 25th, 50th, 75th, 90th, 95th, and 97th percentiles were presented in Table 2. Infants from the multiparous mothers were plotted in the same way. The Table 3 showed smoothed percentiles for birthweight (in grams) of later-born male and female. As the gestational age (week) increases, the growth curves for various percentiles are smooth and increasing steadily. In the 10th, 50th, and 90th percentile graphs of singleton births, boys showed higher BWs than those of girls in the total infant graphs at each GA; moreover, Single births showed weight gained the most at 36–37 weeks, and growth slowed after 37 weeks (Fig. 1).

Table 1.

Smoothed percentiles for birthweight (grams) of male and female.

GA (weeks) Male babies smoothed percentiles Female babies smoothed percentiles
N C3 C10 C25 C50 C75 C90 C97 L M S N C3 C10 C25 C50 C75 C90 C97 L M S
25 64 555 632 700 772 848 926 1022 −0.26 772 326 23 635 705 768 834 903 972 1054 −0.23 834 153
26 228 634 715 787 862 940 1022 1124 −0.28 862 459 107 694 776 850 929 1011 1095 1197 −0.26 929 654
27 572 722 810 887 967 1052 1140 1251 −0.33 967 137 310 757 855 942 1035 1133 1236 1367 −0.35 1035 544
28 1273 810 911 1000 1092 1189 1291 1422 −0.37 1092 365 790 826 943 1047 1157 1275 1402 1571 0.14 1157 358
29 1698 889 1011 1117 1228 1344 1468 1630 −0.29 1228 289 1118 900 1040 1163 1293 1433 1589 1805 0.15 1293 408
30 2626 966 1110 1234 1363 1499 1646 1839 −0.28 1363 309 1670 981 1147 1289 1437 1599 1781 2037 0.09 1437 321
31 3795 1058 1223 1365 1512 1668 1835 2056 0.17 1512 305 2328 1087 1273 1433 1599 1777 1976 2253 0.16 1599 346
32 5605 1181 1366 1525 1689 1862 2047 2289 −0.13 1689 306 3750 1223 1427 1602 1784 1977 2186 2465 −0.15 1784 338
33 8513 1326 1528 1702 1882 2070 2270 2526 −0.08 1882 346 5726 1385 1601 1790 1986 2191 2408 2685 −0.10 1986 338
34 15824 1477 1695 1883 2078 2280 2492 2760 0.06 2078 336 11030 1569 1796 1995 2204 2420 2644 2920 0.08 2204 359
35 28548 1659 1888 2087 2294 2507 2728 3000 0.12 2294 360 20166 1768 2001 2208 2426 2651 2881 3158 0.11 2426 363
36 66292 1849 2085 2295 2513 2737 2966 3240 0.18 2513 367 46054 1980 2209 2418 2641 2872 3107 3387 0.13 2641 372
37 239695 2068 2303 2517 2744 2978 3213 3490 0.16 2744 366 165833 2214 2431 2635 2859 3094 3331 3609 0.16 2859 369
38 621082 2319 2540 2750 2979 3217 3455 3730 0.15 2979 367 474002 2399 2602 2800 3022 3257 3492 3762 0.14 3022 361
39 849913 2504 2713 2918 3147 3388 3627 3897 0.15 3147 372 751125 2510 2708 2907 3132 3372 3610 3878 0.33 3132 362
40 709857 2610 2818 3025 3260 3507 3750 4018 0.14 3260 383 688392 2564 2769 2976 3210 3458 3702 3974 0.30 3210 374
41 187571 2654 2870 3087 3332 3590 3841 4115 0.13 3332 392 197254 2634 2849 3064 3308 3565 3816 4093 0.28 3308 385
42 21317 2731 2954 3178 3431 3696 3953 4232 −0.28 3431 410 22022 2623 2846 3070 3324 3594 3858 4151 −0.23 3324 406
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Table 2.

Smoothed percentiles for birthweight (grams) of first born male and female.

GA (weeks) First born male babies smoothed percentiles First born female babies smoothed percentiles
N C3 C10 C25 C50 C75 C90 C97 L M S N C3 C10 C25 C50 C75 C90 C97 L M S
25 12 657 725 788 856 926 993 1067 −0.26 856 326 6 600 673 738 805 872 936 1007 −0.27 805 798
26 58 721 803 878 958 1040 1120 1210 −0.28 958 459 28 667 753 830 910 990 1069 1157 −0.27 910 1252
27 138 792 892 982 1077 1174 1271 1383 −0.33 1077 137 80 732 833 923 1016 1112 1207 1318 −0.30 1016 1102
28 307 869 993 1101 1213 1327 1443 1584 −0.37 1213 365 198 803 920 1025 1135 1249 1366 1506 −0.39 1135 1161
29 440 953 1101 1227 1355 1487 1624 1796 −0.29 1355 289 297 883 1021 1144 1273 1408 1550 1725 −0.39 1273 1352
30 670 1047 1216 1358 1502 1650 1807 2008 −0.28 1502 309 448 968 1128 1270 1419 1577 1743 1955 −0.26 1419 1443
31 979 1162 1352 1511 1671 1838 2014 2243 0.17 1671 305 606 1065 1250 1413 1582 1760 1948 2189 0.27 1582 1602
32 1450 1300 1508 1684 1862 2046 2241 2490 −0.13 1862 306 1018 1190 1400 1581 1768 1962 2165 2420 0.06 1768 1764
33 2129 1461 1680 1869 2063 2262 2468 2726 −0.08 2063 346 1573 1351 1574 1766 1964 2167 2376 2633 −0.12 1964 1975
34 4195 1640 1867 2067 2273 2483 2697 2954 0.06 2273 336 3054 1547 1776 1976 2181 2391 2604 2859 −0.23 2181 2193
35 7699 1824 2058 2266 2482 2701 2919 3173 0.12 2482 360 5813 1752 1984 2189 2403 2620 2837 3092 −0.10 2403 2418
36 17663 2040 2272 2483 2704 2930 3152 3406 0.18 2704 367 12894 1956 2182 2387 2604 2826 3046 3302 0.19 2604 2614
37 59435 2274 2495 2702 2927 3159 3388 3648 0.16 2927 366 43413 2182 2394 2595 2813 3040 3266 3525 0.11 2813 2828
38 151706 2461 2668 2872 3099 3337 3572 3835 0.15 3099 367 122852 2368 2566 2761 2979 3209 3438 3697 0.25 2979 2996
39 222147 2579 2784 2990 3223 3469 3710 3975 0.15 3223 372 206784 2485 2680 2876 3098 3334 3567 3827 0.15 3098 3116
40 709857 2610 2818 3025 3260 3507 3750 4018 0.14 3260 383 187135 2547 2748 2951 3183 3428 3667 3930 0.14 3183 3199
41 187571 2654 2870 3087 3332 3590 3841 4115 0.13 3332 392 58249 2622 2829 3040 3281 3535 3780 4046 0.14 3281 3297
42 21317 2731 2954 3178 3431 3696 3953 4232 −0.28 3431 410 5434 2603 2817 3035 3286 3549 3803 4075 −0.20 3286 3297
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Table 3.

Smoothed percentiles for birthweight (grams) of later born male and female.

GA (weeks) Later born male babies smoothed percentiles Later born female babies smoothed percentiles
N C3 C10 C25 C50 C75 C90 C97 L M S N C3 C10 C25 C50 C75 C90 C97 L M S
25 52 625 712 787 865 947 1035 1153 −0.36 865 211 17 619 685 747 814 885 959 1050 −0.20 814 146
26 170 722 814 892 974 1060 1153 1276 −0.38 974 316 79 688 769 843 923 1008 1098 1211 −0.33 923 499
27 434 817 919 1008 1100 1197 1303 1442 −0.33 1100 252 230 760 858 947 1042 1143 1252 1393 −0.23 1042 630
28 966 898 1019 1124 1233 1349 1475 1642 −0.35 1233 339 592 835 953 1058 1168 1288 1419 1594 −0.25 1168 394
29 1258 971 1113 1236 1365 1502 1650 1849 −0.30 1365 258 821 916 1054 1176 1304 1443 1598 1814 −0.23 1304 416
30 1956 1062 1226 1368 1517 1675 1847 2074 −0.25 1517 287 1222 1003 1165 1305 1452 1613 1795 2054 −0.23 1452 336
31 2816 1187 1370 1529 1696 1871 2059 2305 0.27 1696 288 1722 1105 1290 1450 1618 1800 2006 2297 0.21 1618 347
32 4155 1335 1535 1708 1888 2077 2278 2535 −0.23 1888 330 2732 1234 1438 1615 1802 2001 2221 2518 −0.12 1802 354
33 6384 1483 1701 1889 2084 2287 2500 2769 −0.18 2084 343 4153 1391 1607 1796 1995 2205 2428 2716 −0.33 1995 336
34 11629 1664 1894 2094 2302 2516 2739 3016 0.08 2302 353 7976 1575 1800 1999 2208 2426 2652 2931 0.11 2208 369
35 20849 1859 2096 2306 2524 2750 2981 3262 0.22 2524 380 14353 1774 2007 2214 2432 2659 2890 3169 0.16 2432 373
36 48629 2081 2317 2531 2759 2995 3234 3517 0.28 2759 383 33160 1991 2221 2430 2653 2885 3121 3404 0.36 2653 385
37 180260 2336 2557 2767 2996 3236 3476 3753 0.36 2996 376 122420 2231 2447 2651 2875 3110 3348 3627 0.27 2875 373
38 469376 2521 2730 2934 3163 3404 3643 3914 0.35 3163 371 351150 2412 2614 2812 3033 3269 3504 3772 0.25 3033 362
39 627766 2622 2831 3039 3273 3520 3763 4033 0.25 3273 376 544341 2519 2716 2914 3139 3379 3616 3883 0.24 3139 364
40 526358 2661 2878 3095 3341 3600 3852 4128 0.15 3341 392 501257 2568 2772 2978 3213 3461 3706 3978 0.09 3213 376
41 134437 2738 2962 3188 3443 3709 3968 4249 0.34 3443 403 139005 2633 2847 3063 3308 3566 3818 4094 0.24 3308 389
42 16498 2714 2949 3187 3457 3742 4018 4319 −0.25 3457 424 16588 2617 2843 3070 3327 3599 3865 4160 −0.17 3327 415
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Figure 1.

Figure 1

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Smoothed percentiles for weight (gms) by gestational age (week) (weeks) for (A) male and (B) female babies. Smoothed percentiles for weight (gms) by gestational age (week) (weeks) for (C) male and (D) female babies from primiparous mothers. Smoothed percentiles for weight (gms) by gestational age (week) (weeks) for (E) male and (F) female babies from multiparous mothers. (A) We first showed the male and gestational age (week)-specific birthweight distributions from mothers who may had ever delivered or did not give birth ever. Curve fitting of the third percentile birthweight of each gestational age (week) (25–42 gestational age (week)) was presented. Above the third percentile, it is the 10th percentile, the 25th percentile, the 50th percentile, the 75th percentile, the 90th percentile, and the 97th percentile of each gestational age (week). (B) Showed the female and gestational age (week)-specific birthweight distributions from mothers who may give birth once or not. (C) Representative the male and gestational age (week)-specific birthweight distributions from primiparous mothers. (D) Representative the female and gestational age (week)-specific birthweight distributions from primiparous mothers. (E) Representative the male and gestational age (week)-specific birthweight distributions from multiparous mothers. (F) Representative the female and gestational age (week)-specific birthweight distributions from multiparous mothers.

We use the Birth certificate data between Jan 1st, 2017 and Oct 31st, 2017 as our test dataset which were categorized into the 10th and 90th percentiles of birthweight for gestational age (week) (i.e., SGA, LGA) using cut points derived from our research standards, China’s 2015 research standards13 and INTERGROWTH-21st standards. The Table 4 provides the sex-specific proportions of these births at 25–42 gestational age (week) ranges.

Table 4.

Comparison with the China’s 2015 Standard and INTERGROWTH-21st Standard.

GA (weeks) N Guangdong Standard China’s 2015 Standard INTERGROWTH-21st Standard
SGA(%) AGA(%) LGA(%) SGA(%) AGA(%) LGA(%) SGA(%) AGA(%) LGA(%)
25 22 13.64 81.82 4.55 0 90.91 9.09
26 83 13.25 79.52 7.23 2.41 90.36 7.23
27 229 12.66 82.53 4.80 2.62 93.89 3.49
28 493 11.76 77.08 11.16 3.85 89.45 6.69
29 691 11.14 78.00 10.85 3.47 90.45 6.08
30 946 11.31 80.55 8.14 5.39 89.75 4.86
31 1343 11.24 79.75 9.01 5.96 88.24 5.81
32 2090 11.29 80.57 8.13 6.36 87.94 5.69
33 3448 12.30 79.79 7.92 7.45 87.91 4.64 3.65 88.31 8.03
34 6562 10.06 81.04 8.90 7.99 87.11 4.91 5.61 86.64 7.76
35 11507 10.87 79.37 9.76 8.65 86.73 4.62 6.41 85.57 8.01
36 26147 11.01 79.97 9.01 8.57 86.71 4.72 6.02 85.15 8.84
37 93877 9.78 80.33 9.89 9.90 85.81 4.29 4.71 84.81 10.48
38 262138 10.67 78.49 10.84 11.10 84.50 4.40 5.10 85.27 9.62
39 376992 8.79 80.78 10.43 12.23 83.47 4.30 6.46 84.56 8.99
40 377739 11.43 79.76 8.80 16.12 79.53 4.35 11.61 81.58 6.82
41 75187 9.55 80.69 9.76 13.72 80.07 6.21 11.96 81.66 6.38
42 5870 10.51 79.98 9.51 16.75 76.78 6.47 19.01 76.15 4.84
total 1245364 10.21 79.91 9.88 12.93 82.59 4.48 7.98 83.65 8.37
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The curves show the incidence of SGA at each gestational age (week), and the three criteria are compared (Fig. 2). In the same way, the incidence of LGA and the incidence of AGA in each gestational age (week) was observed by these three criteria. As the INTERGROWTH-21st national standards only cover 33–42 weeks of gestational age (week), we only calculate the 10th and 90th percentiles of birthweight for gestational age (week) (i.e., SGA, LGA) at 33–42 weeks using this reference. As expected, the thresholds derived from INTERGROWTH-21st standards below the 10th and above the 90th percentile across all gestational age (week) categories were from 3.65% to 19.01%. On the other hand, the thresholds derived from China’s 2015 research standards captured a greater proportion of SGA births (16.75% in 42 gestational age (week), while included only 9.09% (25 gestational age (week)) of LGA births within the gestation ranges in their research dataset. In our research, the 10th and 90th-percentile proportions of birthweight for gestational age (week) were relatively stable. The maximum value was found in SGA of 25 gestational age (week) (13.64%), while the minimum value is found in LGA of 25 gestational age (week) (4.55%). The overall prevalence of SGA estimated by our standards, the China’s 2015 research standards and INTERGROWTH-21st standards, were 10.21%,12.93% and 7.98%, respectively, whereas the overall prevalence of LGA was 9.88%, 4.48% and 8.37%, respectively.

Figure 2.

Figure 2

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Comparison with the China 2015 Standard and INTERGROWTH-21st Standard. (A) In each gestational age (week), the SGA rate is calculated by dividing the number of infants who are judged as SGA by the total number of infants born during this gestational age (week). The number of AGA infants were determined by three criteria. (B) The LGA rate is calculated by dividing the number of infants who are judged as LGA by the total number of infants born during this gestational age (week). The number of LGA infants were determined by three criteria. (C) The AGA rate is calculated by dividing the number of infants who are judged as AGA by the total number of infants born during this gestational age (week). The number of AGA infants were determined by three criteria.

Discussion

The birthweight references included newborns with adverse pregnancy outcomes. These references served the purpose of comparing newborns with the general population, but they were not the prescribed criteria on how newborns should grow under the optimal pregnancy conditions. Infant birthweight is influenced by both environmental and genetic factors; therefore, it is important to identify the percentile distribution of birthweight during pregnancy using recent data to evaluate infants16. The birthweight standard for Chinese infants was published in 1988, which was nearly three-decade old and cannot reflect the current newborns’ situation17. The male birthweight is bigger than that of female; thus, the birthweight curve should be sex-specific. For example, a cross-sectional population-based study in Australia between 1998 and 2007, by comparing term babies of the same gestational age (week), the median birthweight is 0–25 g heavier for male infants, and 5–45 g higher for female infants than 10 years ago11. In our analyses, from 25 gestational age (week) to 42 gestational age (week), the average birthweight of males is from 903 g to 3470 g. The average birthweight of females is from 844 g to 3341 g. The 3rd, 5th, 10th, 50th, 90th, 95th and 97th centiles birthweight of males is heavier than that of girls. In 1988, Zhang et al.18 reported the physical development of different gestational age (week) neonates in 15 cities in China. Their study showed that from 28 gestational age (week) to 42 gestational age (week), the birthweight of the male neonate from 50th were from 1234 g to 3405 g. The 50th birthweight of female newborns were from 1103 g to 3292 g. In 2015, a nationwide neonatology network in China made a survey in 63 hospitals. And the mean birthweight of male was (3271 ± 576) g, the mean birthweight of female was (3188 ± 528) g13. Compared with references using previously published percentiles in Australia, increases in age-specific 10th and 90th percentiles observed from current data will therefore increase the rate of SGA and decrease the rate of LGA for term births11. In the United States, the 50th percentile birthweight of male and female at 40 gestational age (week) were respectively 3572 g and 3431 g in 20119, which were higher than those published in China’s 2015 research birthweight standard (3482 g for male and 3349 g for female). In Guangdong population, the birthweight at 50 percentiles was 3339 g and 3213 g for male and female respectively. In general, birthweight in China is smaller compared to that in the developed countries, while the BWs in Guangdong province is even smaller than China’s average.

The average birthweight of primipara male infants at 40 gestational age (week) was 120 g higher than that of female. The largest mean birthweights gap between the male and the female infants was 135 g at 41 gestational age (week). These gender differences are bigger than the ones in India where the term firstborn males were found to be 45 g heavier than females on average (the mean birthweight were 2934 g and 2889.5 g for males and females respectively). When considering later born preterm babies, the males outweighed the female babies by 111 grams. The mean birthweight were 2089 g and 1978 g respectively19.

In Australia, a mean increase in birthweight of 23 g from 1990 to 2005 for male babies in New South Wales could be translated into an 18% increase in those identified as SGA, or 21% increase in those identified as LGA for females. The test data from 2017 shows between 25 and 27-week gestational age (week), we observed the highest prevalence (12.66~13.64%) of SGA by applying the new Guangdong Province birthweight standard. In contrast, by applying the same standard, the incidence of SGA was the lowest (8.79%) in 39 gestational age (week). Relative to the other two standards, the prevalence of LGA was the highest estimated by our research standards in general. The use of the other two percentiles may lead to the unnecessary intervention and anxiety to the parents of babies whose weight fall in the range of lower and upper centiles according to our centiles. With the China’s 2015 research standards, the total incidence of SGA is the largest (12.93%), while the total incidence of SGA by our research and International standards is 10.21% and 7.98% respectively. On the contrary, the total incidence of LGA by the 2015 China standard is lowest (4.48%) compared to the other two standards.

A study has shown that infants defined by Guangdong new birthweight reference (a new reference) as SGA, 15.3–47.7% (depending upon gestational age (week)) were considered appropriate for gestational age (week) (AGA) by the currently used reference of China. Of the infants defined as SGA by the new reference, 92% with gestational age (week) between 34 and 36 weeks and 14.3% between 37 and 41 weeks were considered AGA by the global reference20.

Our method to assess gestational age (week) may be constrained by methodology. Ideally, gestational age (week) should be combined with the assessment of mother’s last menstrual period, prenatal ultrasound measurement, and postnatal assessment; such practice could be found from the National Perinatal Data Collection (NPDC) of the Australian Institute of Health and Welfare (AIHW) National Perinatal Statistics Unit11,21 and Scottish neonatal birthweight percentiles by Bonellie et al.22. However, in actual clinical practice in Guangdong, the gestational age (week) assessment was mainly assessed by mother’s last menstrual period. If the conditions of midwifery technical services of medical institutions allow, the early pregnancy ultrasound correction of gestational age (week) may have been carried out. Although the ultrasound examination to assess the gestational age (week) has been commonly used, and the regular pregnancy test performed in the early gestational age (week) also becomes popular, it is difficult to collect obstetric information; and therefore, most of the newborn’s gestational age (week)s are still solely based on mother’s last menstrual time.

Author Contributions

Prof Zhao and Fei Yao conceptualized and designed the study and the data collection instruments, and coordinated and supervised data collection, critically reviewed the manuscript, and approved the final manuscript as submitted. Huazhang Miao carried out the main data processing and analysis, drafted the initial manuscript, and approved the final manuscript as submitted. Bing Li and Yuntao Wu participated in the data collection and carried out the initial analyses. Prof Zhao and Fei Yao assisted the data processing and model construction, critically reviewed the manuscript. All authors have reviewed and revised the manuscript, and approved the final manuscript as submitted.

Competing Interests

The authors declare no competing interests.

Footnotes

Fei Yao, Huazhang Miao and Bing Li contributed equally to this work.

Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

References

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