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Background INTERGROWTH-21st Newborn Cross-Sectional Study (NCSS) charts were established and recommended for global application. However, whether one international reference is appropriate for all populations is still unclear. We aim to compare the updated Chinese birth size charts by gestational age with INTERGROWTH-21st NCSS charts. Methods A cross-sectional survey was carried out, and the birth weight, length and head circumference of 24,375 infants born after uncomplicated pregnancies at gestational age ranging from 24+0 to 42+6 weeks were measured in 13 cities in China from 2015 to 2018. Growth charts were constructed. The measurements of all these infants were evaluated by the methods of calculating their Z scores using the INTERGROWTH-21st standards. The prevalence of small for gestational age (SGA) and large for gestational age (LGA) based on birth weight was analyzed using Chinese charts and INTERGROWTH-21st charts. Results The mean Z scores were 0.10 for birth weight, 0.35 for length and − 0.02 for head circumference. Compared to the INTERGROWTH-21st charts, the Chinese birth weight percentile curves were higher except for the 90th percentile at 29–37 weeks gestational age, and the length percentile curves were higher after 33 weeks gestational age, while the 10th percentile of the head circumference was lower and the other percentiles were similar. The prevalence of SGA was 10.1% [95% confidence interval (CI) = 9.7%–10.5%] using the Chinese birth weight chart and 6.5% (95% CI = 6.2%–6.8%) using the INTERGROWTH-21st birth weight chart. The prevalence of LGA was 9.9% (95% CI = 9.5%–10.2%) and 8.2% (95% CI = 7.9%–8.6%) using the Chinese and INTERGROWTH-21st birth weight charts, respectively. Conclusions Chinese birth size charts based on infants born after uncomplicated pregnancies were different from the INTERGROWTH-21st charts. Differences in the classification of newborns by the two charts should receive attention, and whether the application of INTERGROWTH-21st in Chinese newborns will lead to misclassification needs to be validated in future clinical practice.

Background With the rapid development of social economy in China, children's dietary behaviors and lifestyle has undergone great changes. Picking eating, inappropriate protein intake, inactive lifestyle may lead to children's poor physical growth. Especially for preschool children who are in the key period for the formation of dietary habits and lifestyle, early identification of problems in their diet and living habits and interventions will be the key procedure to improve the growth and health level of the whole population. Methods All subjects were from a cross-sectional survey in China, a total of 53172 preschool children were included. The anthropometric measurement was completed on site, and dietary behavior, physical activity, sleeping and screen time were collected by face-to-face interview using a self-made questionnaire. Results 1)Among preschool children, 34.0% were picky eaters, the growth level of them was lower than non-picky eaters, the height SDS and weight SDS of picky eaters were 0.01 ± 1.00 and 0.10 ± 1.10, and those of non-picky eaters were 0.17 ± 1.01 and 0.17 ± 1.15. The differences were statistically significant (P

BackgroundLittle consensus exists for growth performance of different feeding patterns in infancy. The objective of this study is to assess the growth performance of exclusively breastfed, partially breastfed and formula fed infants in China.MethodsData from a total of 109,052 infants aged 1-Results34.0% and 43.9% of infants were exclusively breastfed and 41.5% and 36.3% were partially breastfed at 4-ConclusionsPartial breastfed and formula fed infants were a little lighter than exclusively breastfed infants in the first half of the first year. Formula fed infants were a little longer than continued breastfed infants in the second half.

The prevalence of stunting, wasting, overweight and their coexistence are various in different populations and they also have changed with social developing and environmental improving. In this paper, we aimed to analyze the prevalence of stunting, wasting, overweight and their coexistence in some developed regions of China. Data were collected in a population-based cross-sectional survey by a multi-stage cluster sampling method in nine cities located in the northern, central, and southern region of China in 2016. Children under seven years (n = 110,491) were measured. WHO growth standards were used to assess the growth status. Stunting, underweight, wasting, overweight and obesity were considered as the primary forms of malnutrition (includes undernutrition and overnutrition) for infant or young children at population-levels. The prevalence of stunting, underweight, wasting, and overweight or obesity were respectively 0.7%, 0.6%, 1.2%, and 7.6%. Most of these children (95.4%) suffered from one form of malnutrition, and only 0.2% of them concurrently stunted and wasted, 0.4% concurrently stunted and overweight, 1.7% concurrently stunted and underweight, 2.3% concurrently underweight and wasted. Among stunted children, 91.2% were appropriate body proportion, and only 2.3% were wasted, 6.5% were overweight or obesity. Among overweight or obese children, only 0.6% were stunted, whereas, 15.8% were high stature and 83.6% were the appropriate ranges of stature. Sex, age, urban/suburban, and region were associated with these primary forms of malnutrition in the multivariate logistic analysis. In conclusion, we found that the coexistence of stunting and overweight was not common at both population-level and individual-level. The situation for undernutrition had significantly improved, and overweight may be the leading public health issue for children under seven years in the nine cities of China.

To examine if economic development in China correlates with physical growth among Chinese children and adolescents.The height, body weight and physical activity level of children and adolescents aged 18 years and under, as well as dietary data, were obtained from seven large surveys conducted in China between 1975 and 2010. Chinese economic development indicators were obtained from the World Bank. Trends in body weight, height, economic data and diet were examined. Tests were conducted to check for correlations between height at 17 years of age and three indicators of economic development: gross domestic product, urbanization and infant mortality rate. Regional differences in physical growth were assessed.Between 1975 and 2010, the growth of children and adolescents improved in tandem with economic development. The largest increment in height was observed during the period of puberty. Regional inequalities in nutritional status were correlated with disparities in economic development among regions. Over the past two decades, undernutrition declined among children less than 5 years of age, but in 2010 underweight and stunting were still common in poor rural areas. A large increase in obesity was observed in both urban and rural areas, but especially in large cities and, more recently, in small and medium-sized cities and affluent rural areas.The average weight of children and adolescents has been increasing progressively since the 1970s. Current strategies to combat both child undernutrition and obesity need to be improved, especially in poor rural areas.Examiner si le développement économique en Chine est corrélé avec la croissance physique chez les enfants et adolescents chinois.La taille, le poids et le niveau d'activité physique des enfants et adolescents âgés de 18 ans et moins, ainsi que les données relatives à leur alimentation, ont été obtenus à partir de 7 grandes études menées en Chine entre 1975 et 2010. Les indicateurs du développement économique chinois ont été obtenus auprès de la Banque mondiale. Les tendances en matière de taille, de poids, des données économiques et de l'alimentation ont été examinées. Des tests ont été effectués pour vérifier les corrélations entre la taille à l'âge à 17 ans et 3 indicateurs du développement économique: le produit national brut, le taux d'urbanisation et le taux de mortalité infantile. Les différences régionales en matière de croissance physique ont été analysées.Entre 1975 et 2010, la croissance des enfants s'est améliorée en tandem avec le développement économique. La plus grande augmentation de taille a été observée pendant la puberté. Les inégalités régionales en matière d'alimentation ont été corrélées avec les disparités du développement économique existant entre les régions. Au cours des 2 dernières décennies, la dénutrition a diminué chez les enfants de moins de 5 ans, mais en 2010, les insuffisances pondérales et les retards de croissance étaient toujours courants dans les zones rurales pauvres. Une forte augmentation de l'obésité a été observée à la fois dans les zones urbaines et rurales, mais particulièrement dans les grandes villes et, plus récemment, dans les villes de petite et moyenne taille et dans les zones rurales riches.Le poids moyen des enfants et adolescents a augmenté progressivement depuis les années 1970. Les stratégies actuelles de lutte contre la dénutrition et l'obésité chez les enfants doivent être améliorées, en particulier dans les zones rurales pauvres.Examinar si el desarrollo económico de China está relacionado con el crecimiento físico entre los niños y adolescentes chinos.Se obtuvieron datos sobre la altura, el peso y el nivel de actividad física de niños y adolescentes hasta 18 años, así como datos sobre la dieta, a partir de siete grandes encuestas llevadas a cabo en China entre 1975 y 2010. Los indicadores del desarrollo económico chino se obtuvieron del Banco Mundial. Se examinaron las tendencias en el peso corporal, la altura, los datos económicos y la dieta. Se realizaron pruebas para comprobar la correlación entre la altura a los 17 años de edad y tres indicadores del desarrollo económico: el producto interior bruto, la urbanización y la tasa de mortalidad infantil, y se evaluaron las diferencias regionales en el crecimiento físico.Entre 1975 y 2010, el crecimiento de los niños mejoró a la par que el desarrollo económico. El mayor incremento en la altura se observó durante la pubertad. Las desigualdades regionales en el estado nutricional se correlacionaron con las diferencias de desarrollo económico entre las regiones. En las últimas dos décadas, la desnutrición disminuyó entre los niños menores de cinco años, pero, en 2010, una talla y peso bajos seguían siendo frecuentes en zonas rurales pobres. Se observó un gran aumento de la obesidad tanto en zonas urbanas como rurales, pero especialmente en las grandes ciudades y, más recientemente, en ciudades pequeñas y medianas y en zonas rurales prósperas.El peso medio de los niños y adolescentes ha ido aumentando progresivamente desde la década de 1970. Es necesario mejorar las estrategias actuales para combatir tanto la desnutrición como la obesidad infantil, particularmente, en las zonas rurales pobres.دراسة ما إذا كانت التنمية الاقتصادية في الصين ترتبط بالنمو البدني بين الأطفال والمراهقين في الصين.تم الحصول على طول الأطفال والمراهقين في سن 18 سنة فأقل وأوزان أجسامهم ومستوى نشاطهم البدني، بالإضافة إلى بيانات النظام الغذائي، من سبع دراسات استقصائية كبرى تم إجراؤها في الصين في الفترة بين عامي 1975 و2010. وتم الحصول على مؤشرات التنمية الاقتصادية في الصين من البنك الدولي. وتم دراسة الاتجاهات في وزن الجسم والطول والبيانات الاقتصادية والنظام الغذائي. وأجريت الاختبارات للكشف عن الارتباطات بين الطول في سن 17 عاماً ومؤشرات التنمية الاقتصادية الثلاثة: الناتج المحلي الإجمالي والتوسع العمراني ومعدل وفيات الرضع. وتم تقييم الاختلافات في النمو البدني بين الأقاليم.تحسن نمو الأطفال بين عامي 1975 و2010 بالترادف مع التنمية الاقتصادية. ولوحظت أقصى زيادة في الطول خلال فترة البلوغ. وارتبطت التباينات في الحالة التغذوية بين الأقاليم بالفوارق في التنمية الاقتصادية بين الأقاليم. وعلى مدار العقدين المنصرمين، انخفض نقص التغذية بين الأطفال الأقل من خمسة سنوات ولكن في عام 2010 ظل نقص الوزن والتقزم شائعين في المناطق الريفية الفقيرة. ولوحظت زيادة كبيرة في السمنة في المناطق الحضرية والريفية على حد سواء، وبالأخص في المدن الكبيرة، وفي الآونة الأخيرة لوحظت في المدن الصغيرة ومتوسطة الحجم والمناطق الريفية الغنية.يزداد متوسط وزن الأطفال والمراهقين تدريجياً منذ سبعينيات القرن العشرين. ويجب تحسين الاستراتيجيات الراهنة لمكافحة نقص التغذية والسمنة لدى الأطفال، لا سيما في المناطق الريفية الفقيرة.调查中国的经济发展是否与中国儿童和青少年体格发育有关联。从1975到2010年在中国开展的七个大型调查中获取18岁及以下儿童和青少年的身高、体重和身体活动水平以及饮食数据。从世界银行获取中国经济发展指标。调查体重、身高、经济数据和饮食的趋势。执行检验以检查17岁青少年身高和三项经济发展指标(国内生产总值、城市化和婴儿死亡率)之间的相关性。评估体格发育的地区差异。1975至2010年间,儿童发育随经济发展同步改善。据观察,青春期身高增长最大。地区营养状态不均衡与各个地区经济发展差异有关。在过去二十年中,五岁以下孩子营养不良状况减少,但是在2010年,贫穷农村地区依然普遍存在体重不足和生长迟缓的现象。城市和农村地区都出现大幅增加的肥胖儿童,但在大城市尤其如此,这种情况最近在中小城市和富裕的农村地区也凸显出来。自二十世纪七十年代以来,儿童和青少年的平均体重逐步增加。必须改进当前应对儿童营养不良和肥胖症的策略,在贫穷乡村地区尤其如此。Определить, коррелирует ли экономическое развитие в Китае с физическим ростом китайских детей и подростков.Рост, вес тела и уровень физической активности детей и подростков в возрасте до 18 лет, а также данные по питанию были получены из семи крупных исследований, проведенных в Китае в период с 1975 по 2010 гг. Показатели экономического развития Китая были получены от Всемирного банка. В ходе исследования были рассмотрены изменения показателей массы тела, роста, экономических данных, а также режим питания. Были проведены исследования корреляции роста детей в возрасте 17 лет с тремя показателями экономического развития: валовым внутренним продуктом, уровнем урбанизации и младенческой смертностью. Проведена оценка региональных различий в физическом развитии.В период с 1975 по 2010 гг. рост детей улучшался в соответствии с экономическим развитием. Самый интенсивный рост наблюдался в период полового созревания. Региональные неравенства в уровне питания коррелировали с различиями в экономическом развитии регионов. За последние два десятилетия уровень недостаточного питания снизился среди детей в возрасте до пяти лет, но в 2010 году дефицит массы тела и задержка в росте все еще были широко распространены в бедных сельских районах. Значительное увеличение числа людей, имеющих ожирение, наблюдалось как в городских, так и в сельских районах, но особенно в крупных городах, а в последнее время в малых и средних городах и богатых сельских районах.Начиная с 1970-х годов постепенно увеличивается средний вес детей и подростков. Необходимо совершенствование используемых стратегий по борьбе как с детским недоеданием, так и ожирением, особенно в бедных сельских районах.

Objectives: To report the secular growth changes of Chinese children aged 0–7 years between 1975 and 2005. Methods: Height and weight measurements obtained from four consecutive national surveys were used to analyze the secular trends. Urban-rural difference and regional difference in growth were compared, respectively. Results: A rapid positive secular trend was observed in China over the last three decades, increased by 5.3 and 5.0 cm in height for urban boys and girls at age 6–7 years, respectively. Urban–rural height difference has continuously reduced, but weight difference has gradually widened after 3-years old which results from the excessive weight increase of urban children, 2.68 kg for rural boys aged 6–7 years but 3.26 kg for urban during the 30 years. Clear regional differences in growth are not narrowing over time. Generally, the growth level in eastern China is higher than central-western, successively higher than southern. Conclusions: The rapid positive secular trends will still continue with the rapid socio-economic development in China. Urban-rural height difference will further narrow. Currently no sufficient evidence indicates that growth difference in inter-city has reduced. Weight increases rapidly for urban children, which does not match with height. Am. J. Hum. Biol., 2011. © 2010 Wiley-Liss, Inc.

The objective of this study was to examine the effect of socioeconomic development on secular trend in height among children and adolescents in China. Body height and spermarcheal/menarcheal ages were obtained from two periodic large-scale national representative surveys in China between 1975 and 2010. Chinese socioeconomic development indicators were obtained from the United Nations world population prospects. The effects of plausible determinants were assessed by partial least-squares regression. The average height of children and adolescents improved in tandem with socioeconomic development, without any tendency to plateau. The increment of height trend presented larger around puberty than earlier or later ages. The partial least-squares regressions with gross national income, life expectancy and spermarcheal/menarcheal age accounted for increment of height trend from 88.3% to 98.3% for males and from 82.9% to 97.3% for females in adolescence. Further, through the analysis of the variable importance for projection, the contributions of gross national income and life expectancy on height increment were confirmed to be significant in childhood and adolescence, and the contribution of spermarcheal/menarcheal age was superior to both of them in adolescence. We concluded that positive secular trend in height in China was significantly associated with socioeconomic status (GNI as indicator) and medical and health conditions (life expectancy as indicator). Earlier onset of spermarche and menarche proved to be an important role in larger increment of the trend over time of height at puberty for a population.

To study the body cut-offs of mass index (BMI) for the purpose of screening overweight and obesity for Chinese children and adolescents aged 2 - 18 years.Based on the BMI growth reference values for Chinese children aged 0 - 18, using the common methods to establish the BMI cut-offs for screening overweight and obesity. These methods were having the same empirical percentile or Z scores and the BMI value at 18 years consistent with adults. Three sets of BMI cut-offs, including (BMI₂₄, BMI₂₈), (P₈₅, P₉₅) and (Z₁, Z₂), were initially identified. Differences were compared on different cut-off points and prevalence rates of overweight and obesity with different BMI reference, different values and "prevalence" of overweight and obesity based on "2004 Beijing Child and Adolescent Metabolic Syndrome Study". Cut-offs standards which recommended by the Chinese Working Group on Obesity for Children (WGOC) and by the International Obesity Task Force (IOTF) were also used. Finally the appropriate cut-offs were defined.Three sets of BMI cut-offs for screening overweight and obesity for Chinese children and adolescents aged 2 - 18 years were obtained according to the above mentioned methods for selection. The prevalence rates of overweight and obesity defined by those cut-offs appeared not to be significantly different. Compared with the WGOC, the BMI cut-off points for screening overweight and obesity for both boys and girls from our study were very close to the WGOC', but cut-off points for screening overweight for girls aged 8.5 - 15.5 y was 0.3 - 1.0 kg/m² lower than the WGOC'. Going through the database on screening of "2004 Beijing Children's Metabolic Syndrome Survey", the prevalence of overweight for girls was about 3.4% higher than using the cut-offs of WGOC.Results from this study suggested that the BMI cut-offs passed through the cut-off point of BMI₂₄ and BMI₂₈ at 18 years was appropriate for screening overweight and obesity in Chinese children from 2 to 18 years, and achieved the continuity in age and consistency in screening standard when using the BMI indicator in children and adolescents.

To construct the body mass index (BMI) reference data and curves for Chinese children and adolescents from birth to 18 years of age.Data from two national representative cross-sectional surveys which were The National Growth Survey of Children under 7 years in the Nine Cities of China in 2005 and The Physical Fitness and Health Surveillance of Chinese School Students in 2005. Height (length was measured for children under 3 years) and weight data of 93,702 urban healthy children from nine cities/provinces used to calculate the BMI. The LMS method was used to smooth the BMI, with estimates of L, M, and S parameters, values of percentile and Z-score curves which were required were calculated, and then standardized growth charts were generated. Adult cut-offs for overweight and obesity at 18 years was used to study the cut-offs for children 2 to 18 years of age.The smoothed percentiles and Z-scores reference data and curves of BMI-for-age for boys and girls aged 0-18 years were made out respectively. BMI cut-off values for overweight and obesity for children from 2 to 18 years of age were also defined. At 18 years, the BMI values are equivalent to the overweight cut-off (or =24 kg/m2) and obesity cut-off (or =28 kg/m2) for Chinese adults. Comparison with the reference of the WHO and 2000 CDC for the United States, there were some difference among them, at the 97th percentile curve there was a big difference between Chinese and U. S. adolescents. On the whole, the China BMI curve for boys was higher than the new WHO curve and lower than 2000 CDC at 97 percentile curve, but the China BMI curve for girls was lowest among the three curves. There was also significant difference between China and Japan BMI values at 97 percentile curve.BMI growth curves are very useful in child growth monitoring and nutritional surveillance, discovering overweight and obesity. The BMI growth charts are recommended for use in pediatric clinic and public health service.

To construct the height and weight growth charts for Chinese children and adolescents from birth to 18 years for both clinical and preventive health care uses.Data from two national representative cross-sectional surveys which were The National Growth Survey of Children under 7 years in the Nine Cities of China in 2005 and The Physical Fitness and Health Surveillance of Chinese School Students in 2005. The data from 94,302 urban healthy children were used to set up the database of length/height (length was measured for children under 3 years) and weight. The LMS method was used to smooth the growth curves, with estimates of L, M, and S parameters, values of percentile and Z-score curves which were required were calculated, and then generated standardized growth charts.The 3rd, 10th, 25th, 50th, 75th, 90th, 97th smoothed percentiles curves and -3, -2, -1, 0, +1, +2, +3 Z-scores curves of weight-for-age, length/height-for-age for boys and girls aged 0-18 years were made out respectively. Comparison with the new WHO growth charts and 2000 CDC growth charts for the United States, the results showed that there was some big difference in weight and height among the three growth charts. For boys under 15 years of age and girls under 13 years of age, the China curves are slightly higher than WHO and CDC curves, but after those ages, the China curves fall behind and the difference became larger as age progresses. At the age of 18 years, the Chinese children are 3.5 cm shorter in boys and 2.5 cm shorter in girls as compared with the U. S. children. The difference in weights are very large for the school children, especially in girls. The weight of Chinese boys was 5.9 kg less than that of the U. S. boys at 18 years, and the difference was much bigger in girls, the weight of U.S. girls between 8 to 18 years was 4.1-20.5 kg more than that of Chinese girls at the same age range.The new growth charts of height and weight were based on national survey data and therefore are recommended as the China national growth standards for use in pediatric clinics and public health service. Application of the charts will promote child growth monitoring, discovering early growth disorder, and will be useful to diagnosis of diseases and assessment of therapeutic effects.

To explore the growth patterns and simple mathematic models of height and weight of Chinese children.The original data had been obtained from two national representative cross-sectional surveys which were 2005 National Survey of Physical Development of Children (under 7 years of age) and 2005 Chinese National Survey on Students Constitution and Health (6 - 18 years). Reference curves of height and weight of children under 7 years of age was constructed by LMS method, and data of children from 6 to 18 years of age were smoothed by cubic spline function and transformed by modified LMS procedure. Growth velocity was calculated by smoothed values of height and weight. Simple linear model was fitted for children 1 to 10 years of age, for which smoothed height and weight values were used.(1) Birth length of Chinese children was about 50 cm, average length 61 cm, 67 cm, 76 cm and 88 cm at the 3rd, 6th, 12th and 24th month. Height gain was stable from 2 to 10 years of age, average 6 - 7 cm each year. Birth length doubles by 3.5 years, and triples by 12 years. The formula estimating average height of normal children aged 2 - 10 years was, height (cm) = age (yr) x 6.5 + 76 (cm). (2) Birth weight was about 3.3 kg. Growth velocity was at peak about 1.0 - 1.1 kg/mon in the first 3 months, decreased by half and was about 0.5 - 0.6 kg/mon in the second 3 months, and was reduced by a quarter, which was about 0.25 - 0.30 kg/mon, in the last 6 months of the first year. Body mass was up to doubles, triples and quadruple of birth weight at about the 3rd, 12th and 24th month. Average annual gain was about 2 kg and 3 kg from 1 - 6 years and 7 - 10 years, respectively. The estimated formula for children 1 to 6 years of age was weight (kg) = age (yr) x 2 + 8 (kg), but for those 7 - 10 years old, weight (kg) = age (yr) x 3 + 2 (kg).Growth patterns of height and weight at the different age stages were summarized for Chinese children, and simple reference data of height and weight velocity from 0 to 18 years and approximate estimation formula from 1 - 10 years was presented for clinical practice.

Background Family-based child obesity prevention and control strategy has not yet established in many countries or regions, including China, thus what it needs to do now is to continuously develop and improve the strategies. The purpose of this study were to describe a wider spectrum of risk factors of obesity among preschool children and add to the mounting evidence for further improving suggested intervention measures in future family-based programs. Methods Data was collected as part of a series of national epidemiological surveys in childhood conducted in 9 Chinese cities. A population-based, 1:1 matched case–control design was employed to examine risk factors of obesity by means of conditional logistic regression. Obesity was defined as the International Obesity Task Force (IOTF) BMI-for-age cut offs. Eligible subjects were 1234 boys and 610 girls aged 3–7 years in 1996 and 2290 boys and 1008 girls in 2006, including obese and non-obese. Results High birth weight, gestational hypertension and parents’ BMI were closely associated with childhood obesity. Breast feeding in the first 4 months was a protective factor in univariate model in 2006 (OR = 0.834, P = 0.0234), but the association was not seen in multivariate. Appetite, eating speed, daily time and intensity for outdoor activities, night sleep time, and time for TV viewing were identified statistically by multivariate model. Those children brought up in extended family or mainly raised by their grandparents or lived in high income or low education families might have an increased risk of becoming obese. Parents’ attitudes on weight control of their children significantly differed between obese and non-obese groups. Discussion A wider spectrum of risk factors and an empirical aggregation of family-related risk factors are discussed to further improve future family-based child obesity prevention and control strategies. Most of the risk factors identified by this study presented ranked or quantitative characteristics which might be transformed from unhealthy threshold to healthy range by behavior modification. Some variables are likely to interact each other, such as appetite and eating speed, or outdoor activity and TV viewing, or BMI and income, but which needs to be further explored in future surveys. Conclusions The family-related risk factors were summarized from our identified risk factors of obesity among preschool children which strongly supported the further development of family-based programs in preschool period.