A hospital-based birth weight analysis using computerized perinatal data base for a Chinese population

PM2.5 exposure increases the risk of preterm birth in pre-pregnancy impaired fasting glucose women: A cohort study in a Southern province of China

Previous studies have indicated maternal exposure to particles with aerodynamic diameter <2.5 μm (PM_2.5) is associated with preterm birth (PTB). However, no study has investigated this effect in pre-pregnancy impaired fasting glucose (IFG) women. This study aimed to differentiate the effects of maternal PM_2.5 exposure on PTB between pre-pregnancy IFG and normoglycemia women, and to further identify the susceptible window. This cohort study was conducted between January 2014 and December 2017 in 21 Chinese cities. All the recruited women received pre-pregnancy fasting serum glucose (FSG) tests and were followed up for their delivery outcomes. The PM_2.5 exposures were estimated by the daily air pollution concentrations of the nearby monitors. Women with FSG below 7.0 mmol/L were included in the analysis. We employed the Cox proportional hazards models to examine whether PM_2.5 exposure was associated with PTB. 237957 women were included and 7055 (3.0%) of them were pre-pregnancy IFG. During the entire pregnancy, we found 24.1% (HR = 1.241; 95% CI: 1.069, 1.439), 61.8% (HR = 1.618; 95% CI: 1.311, 1.997) and 18.6% (HR = 1.186; 95% CI: 1.004, 1.402) of increases in risk for all PTB, early PTB (20-33 gestational weeks) and late PTB (34-36 gestational weeks) among the pre-pregnancy IFG women, and 15.9% (HR = 1.159; 95% CI: 1.127, 1.192), 33.9% (HR = 1.339; 95% CI: 1.255, 1.430) and 13.2% (HR = 1.132; 95% CI: 1.098, 1.168) of increases in risk for all PTB, early PTB and late PTB among the normoglycemia women, with each 10 μg/m³ increment of PM_2.5 exposure, respectively. Furthermore, PM_2.5 exposure had the strongest effect on all PTB during trimester 1 (0-12 gestational weeks) among the pre-pregnancy IFG women, compared with the less strong effect during trimester 1 among the normoglycemia women. In conclusion, pre-pregnancy IFG increases the risk of PTB attributed to PM_2.5, especially during trimester 1. Moreover, the effects of PM_2.5 are greater on early PTB than late PTB for both pre-pregnancy IFG and normoglycemia women.

Maternal PM2.5 exposure associated with stillbirth: A large birth cohort study in seven Chinese cities

BACKGROUND

Maternal exposure to fine particulate matter (PM_2.5) has been associated with a few adverse birth outcomes. However, its effect on stillbirth remains unknown in China, especially the susceptible windows and potential modifiers.

OBJECTIVE

This study aimed to evaluate the associations between maternal PM_2.5 exposure and stillbirth in seven Chinese cities.

METHODS

We used birth cohort data of 1,273,924 mother-and-birth pairs in seven cities in southern China between 2014 and 2017 to examine these associations. Pregnant women were recruited in the cohort at their first visit to a doctor for pregnancy, and stillbirths were recorded at the time of birth. Air pollution exposures were assessed through linking daily air pollutant concentrations from nearby monitoring stations to the mother's residential community. Cox regression models were applied to determine the associations between PM_2.5 and stillbirth for different gestational periods.

RESULTS

Among the participants, 3150 (2.47‰) were identified as stillbirth cases. The hazard ratio (HR) of stillbirths was 1.52 (95% CI: 1.42, 1.62) for each 10 μg/m³ increase in PM_2.5 during the entire pregnancy after controlling for some important covariates. Relatively stronger associations were observed during the second trimester [adjusted HR = 1.67 (95% CI: 1.57, 1.77)] than trimesters 1 [HR = 1.44 (95% CI: 1.37, 1.52)] and trimester 3 [HR = 1.23 (95% CI: 1.16, 1.30)]. Stratified analyses also showed a stronger association among pregnant women without previous pregnancy and previous delivery experiences.

CONCLUSION

The study indicates that maternal exposure to PM_2.5, especially during the midpoint period of pregnancy, might increase the risk of stillbirths. Maternal previous pregnancy and delivery may modify this association.

Incidence and trend of preterm birth in China, 1990-2016: a systematic review and meta-analysis

OBJECTIVES

To update the WHO estimate of preterm birth rate in China in 1990-2016 and to further explore variations by geographic regions and years of occurrence.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

Pubmed, Embase, Cochrane Library and Sinomed databases were searched from 1990 to 2018.

ELIGIBILITY CRITERIA

Studies were included if they provided preterm birth data with at least 500 total births. Reviews, case-control studies, intervention studies and studies with insufficient information or published before 1990 were excluded. We estimated pooled incidence of preterm birth by a random effects model, and preterm birth rate in different year, region and by livebirths or all births in subgroup analyses.

RESULTS

Our search identified 3945 records. After the removal of duplicates and screening of titles and abstracts, we reviewed 254 studies in full text and excluded 182, leaving 72 new studies. They were combined with the 82 studies included in the WHO report (154 studies, 187 data sets in total for the meta-analysis), including 24 039 084 births from 1990 to 2016. The pooled incidence of preterm birth in China was 6.09% (95% CI 5.86% to 6.31%) but has been steadily increasing from 5.36% (95% CI 4.89% to 5.84%) in 1990-1994 to 7.04% (95% CI 6.09% to 7.99%) in 2015-2016. The annual rate of increase was about 1.05% (95% CI 0.85% to 1.21%). Northwest China appeared to have the highest preterm birth rate (7.3%, 95% CI 4.92% to 9.68% from 1990 to 2016).

CONCLUSIONS

The incidence of preterm birth in China has been rising gradually in the past three decades. It was 7% in 2016. Preterm birth rate varied by region with the West having the highest occurrence.

Increasing trends in incidence of preterm birth among 2.5 million newborns in Guangzhou, China, 2001 to 2016: an age-period-cohort analysis

Background

The incidence of preterm birth (PTB, < 37 weeks of gestation) has been increasing in China and many other countries in recent years. However, the causes of the increase were not well understood. The current study aims to examine the contribution of maternal age, period of delivery, and maternal birth cohorts to long-term trends in preterm birth in Guangzhou, China.

Methods

In a retrospective population-based study, data were obtained from 2,535,000 singleton live births with 20–43 gestational weeks from 2001 to 2016 and recorded in the Guangzhou Perinatal Health Care and Delivery Surveillance System, in China. The age-period-cohort models were applied to investigate the temporal changes in incidences of PTB, stratified by parity.

Results

The incidence of preterm birth steadily increased from 5.1% in 2001 to 5.9% in 2016, with larger rise in primiparous mothers (from 5.0 to 5.9%) compared to multiparous mothers (from 5.6 to 5.9%). A J-shaped and a V-shaped relationship were found between maternal age and PTB among primiparous and multiparous mothers, respectively. A linear cohort effect was found among primiparous mothers with the lowest risk of PTB [risk ratio (RR) = 0.81, 95% confidence interval (CI): 0.74 to 0.89] in 1961 and the highest risk (RR = 1.06, 95% CI: 1.00 to 1.13) in 1997 compared to the mothers born in 1981. An inverse U-shaped association between maternal birth cohort and PTB was found in multiparous mothers. There were weak decreasing period effects on the trend of overall PTB among multiparous mothers and on the trend of extremely (< 27 weeks) or very (28–31 weeks) PTB among both parity groups during the period of 2001–2012.

Conclusions

Our findings showed the PTB incidences had been increasing in the past 16 years in Guangzhou, China and both maternal age and cohort effects contributed to these trends. Further studies are recommended on the impact of altered maternal age and parity on premature births and corresponding public education and public health policies.

Supplementary Information

Supplementary information accompanies this paper at 10.1186/s12889-020-09739-6.

Independent and Combined Effects of Heatwaves and PM2.5 on Preterm Birth in Guangzhou, China: A Survival Analysis

BACKGROUND

Both extreme heat and air pollution exposure during pregnancy have been associated with preterm birth; however, their combined effects are unclear.

OBJECTIVES

Our goal was to estimate the independent and joint effects of heatwaves and fine particulate matter [PM <2.5μm in aerodynamic diameter (PM2.5)], exposure during the final gestational week on preterm birth.

METHODS

Using birth registry data from Guangzhou, China, we included 215,059 singleton live births in the warm season (1 May-31 October) between January 2015 and July 2017. Daily meteorological variables from 5 monitoring stations and PM2.5 concentrations from 11 sites were used to estimate district-specific exposures. A series of cut off temperature thresholds and durations (2, 3, and 4 consecutive d) were used to define 15 different heatwaves. Cox proportional hazard models were used to estimate the effects of heatwaves and PM2.5 exposures during the final week on preterm birth, and departures from additive joint effects were assessed using the relative excess risk due to interaction (RERI).

RESULTS

Numbers of preterm births increased in association with heatwave exposures during the final gestational week. Depending on the heatwave definition used, hazard ratios (HRs) ranged from 1.10 (95% CI: 1.01, 1.20) to 1.92 (1.39, 2.64). Associations were stronger for more intense heatwaves. Combined effects of PM2.5 exposures and heatwaves appeared to be synergistic (RERIs>0) for less extreme heatwaves (i.e., shorter or with relatively low temperature thresholds) but were less than additive (RERIs<0) for more intense heatwaves.

CONCLUSIONS

Our research strengthens the evidence that exposure to heatwaves during the final gestational week can independently trigger preterm birth. Moderate heatwaves may also act synergistically with PM2.5 exposure to increase risk of preterm birth, which adds new evidence to the current understanding of combined effects of air pollution and meteorological variables on adverse birth outcomes. https://doi.org/10.1289/EHP5117.

Ambient PM2.5 and birth outcomes: Estimating the association and attributable risk using a birth cohort study in nine Chinese cities

BACKGROUND

Previous studies have reported that maternal exposure to particles with aerodynamic diameter <2.5 μm (PM_2.5) is associated with birth outcomes. However, a multicity birth cohort study has not been conducted in China, and the attributable fraction of adverse birth outcomes due to PM_2.5 exposure remains unknown.

METHODS

We examined associations in a birth cohort of 1,455,026 mother-and-live-birth pairs who were followed up from the first hospital visit for pregnancy until the birth of the baby during 2014-2017 in nine cites of the Pearl River Delta (PRD) region, China. The PM_2.5 exposures were estimated based on the air pollution concentrations of the nearby monitors. Cox proportional hazards regressions were employed to examine the associations.

RESULTS

We found 1% (HR = 1.01; 95% CI: 1.00, 1.02), 6% (HR = 1.06; 95% CI: 1.05, 1.07), and 7% (HR = 1.07; 95% CI: 1.06, 1.08) increases in risk of PTB and 20% (HR = 1.20; 95% CI: 1.18, 1.22), 18% (HR = 1.18; 95% CI: 1.15, 1.20), and 20% (HR = 1.20; 95% CI: 1.17, 1.23) increases in risk of LBW, with each 10 μg/m³ increase in PM_2.5 from trimester 1 to trimester 3, respectively. For PTB, highest HRs were observed during trimester 3, as for LBW, stronger effect were observed during trimester 1 and trimester 3. We further estimated that 7.84% (95% CI: 6.21%, 9.50%) of PTB and 14.85% (95% CI: 13.00%, 16.61%) of the LBW cases could be attributable to PM_2.5 exposure during the third trimester.

CONCLUSION

The results indicate that maternal PM_2.5 exposure is a risk factor for both LBW and PTB, and responsible for considerable burdens of PTB and LBW in the Pearl River Delta region.

Identifying windows of susceptibility for maternal exposure to ambient air pollution and preterm birth

Maternal exposure to ambient air pollution has been associated with preterm birth (PTB), however, entire pregnancy or trimester-specific associations were generally reported, which may not sufficiently identify windows of susceptibility. Using birth registry data from Guangzhou, a megacity of southern China (population ~14.5 million), including 469,975 singleton live births between January 2015 and July 2017, we assessed the association between weekly air pollution exposure and PTB in a retrospective cohort study. Daily average concentrations of PM_2.5, PM₁₀, NO₂, SO₂, and O₃ from 11 monitoring stations were used to estimate district-specific exposures for each participant based on their district residency during pregnancy. Distributed lag models (DLMs) incorporating Cox proportional hazard models were applied to estimate the association between weekly maternal exposure to air pollutant and PTB risk (as a time-to-event outcome), after controlling for temperature, seasonality, and individual-level covariates. We also considered moderate PTB (32-36 gestational weeks) and very PTB (28-31 gestational weeks) as outcomes of interest. Hazard ratios (HRs) and 95% confidential intervals (95% CIs) were calculated for an interquartile range (IQR) increase in air pollutants during the study period. An IQR increase in PM_2.5 exposure during the 20th to 28th gestational weeks (27.0 μg/m³) was significantly associated with PTB risk, with the strongest effect in the 25th week (HR = 1.034, 95% CI:1.010-1.059). The significant exposure windows were the 19th-28th weeks for PM₁₀, the 18th-31st weeks for NO₂, and the 23rd-31st weeks for O₃, respectively. The strongest associations were observed in the 25th week for PM₁₀ (IQR = 37.0 μg/m³; HR = 1.048, 95% CI:1.034-1.062), the 26th week for NO₂ (IQR = 29.0 μg/m³; HR = 1.060, 95% CI:1.028-1.094), and in the 28th week for O₃ (IQR = 90.0 μg/m³; HR = 1.063, 95% CI:1.046-1.081). Similar patterns were observed for moderate PTB (32-36 gestational weeks) and very PTB (28-31 gestational weeks) for PM_2.5, PM₁₀, NO₂ exposure, but the effects were greater for very PTB. We did not observe any association between pregnancy SO₂ exposure and the risk of PTB. Our results suggest that middle to late pregnancy is the most susceptible air pollution exposure window for air pollution and PTB among women in Guangzhou, China.

Effect of the 2008 cold spell on preterm births in two subtropical cities of Guangdong Province, Southern China

BACKGROUND

A few studies have reported that low temperatures were associated with an increased risk of preterm birth. However, the effect of extreme weather events, such as cold spell, on preterm birth has not been studied in China.

OBJECTIVE

This study was conducted to evaluate the impact of the 2008 cold spell on preterm birth in two subtropical cities of Guangdong Province.

METHODS

Data of daily preterm birth, air pollution and meteorological variables from 2006 to 2010 were collected in Dongguan and Shenzhen. A Poisson regression with a distributed lag nonlinear model was used to investigate the association between the 2008 cold spell and daily rate of preterm birth for each city.

RESULTS

During the 2008 cold spell, total vaginal preterm births were increased by 22.44% and 21.25% in Dongguan and Shenzhen, respectively. The effect of the cold spell on preterm births lasted for more than 1 week, the lag0-6 days cumulative relative risk (RR) is 1.32 (95% CI: 1.10-1.58) and 1.40 (95% CI: 1.18-1.68) in Dongguan and Shenzhen, respectively. The effects were found to be more pronounced for the pregnant women with 34-36 gestation weeks, maternal age < 35 years group.

CONCLUSION

This study demonstrates that cold spell could increase the risk of preterm births in Dongguan and Shenzhen, and the effect lasts for more than 1 week. Specific measures should be considered to protect the pregnant women, especially the vulnerable subgroups.

Birth weight changes in a major city under rapid socioeconomic transition in China

Estimates of trends in birth weight may be useful in evaluating population health. We aimed to determine whether temporal changes in birth weight have occurred amongst 2.3 million neonates born in Guangzhou, China, during 2001-2015 and investigate the socioeconomic determinants of any changes. Trends in mean birth weight and annualized changes with the associated 95% confidence intervals (CIs) in the incidence of small for gestational age (SGA) and large for gestational age (LGA), defined as birth weight <10^th or >90^th centile respectively for gestational age and sex, were examined using linear and Poisson regression models. We found that mean birth weight declined by 1.07 grams/year from 2001 to 2015. After adjustment for gestational length, the decline in birth weight was attenuated (0.37 grams/year). The incidence of both SGA and LGA significantly decreased during the study period (annual decrease of 1.6% [95% CI, 1.5% to 1.7%] for SGA, 1.6% [95% CI, 1.5% to 1.8%] for LGA). We found a narrowing of disparities in SGA and LGA incidence across different maternal educational levels and residence location. Our results demonstrate that there has been an increase in the proportion of neonates born in the healthy birth weight range in Guangzhou.

Cohort study on maternal cytomegalovirus seroprevalence and prevalence and clinical manifestations of congenital infection in China

Congenital cytomegalovirus (CMV) infection is the leading viral cause of birth defects and developmental disabilities in developed countries. However, CMV seroprevalence and burden of congenital CMV infection are not well defined in China.Cohort of newborns from 5 birthing hospitals in 2 counties of Shandong Province, China, were enrolled from March 2011 to August 2013. Dried blood spots (DBS) and saliva were collected within 4 days after birth for IgG testing for maternal seroprevalence and real-time PCR testing for congenital CMV infection, respectively.Among 5020 newborns tested for CMV IgG, 4827 were seropositive, resulting in CMV maternal seroprevalence of 96.2% (95% confidence interval [CI]:95.6%-96.7%). Of the 10,933 newborns screened for congenital CMV infection, 75 had CMV detected, resulting in an overall prevalence of 0.7% (95% CI: 0.5%-0.9%), with prevalences of 0.4% (14/3995), 0.6% (66/10,857), and 0.7% (52/7761) for DBS, wet saliva, and dried saliva specimens screened, respectively. Prevalence of congenital CMV infection decreased with increasing maternal age (0.9%, 0.6%, and 0.3% among newborns delivered from mothers aged 16-25, 26-35, and >35 years, respectively; P = 0.03), and was higher among preterm infants than full term infants (1.3% vs 0.6%, P = 0.04), infants with intrauterine growth restriction (IUGR) than those without (1.8% vs 0.7%, P = 0.03), and twins or triplets than singleton pregnancies (2.8% vs 0.7%, P = 0.04). None of the 75 newborns exhibited symptomatic congenital CMV infection, and there was no difference in clinical characteristics and newborn hearing screening results between infants with and without congenital CMV infection at birth.Congenital CMV infection prevalence was lower and the clinical manifestations were milder in this relatively developed region of China compared to populations from other countries with similarly high maternal seroprevalence. Follow-up on children with congenital CMV infection will clarify the burden of disabilities from congenital CMV infection in China.

Ambient Temperature and the Risk of Preterm Birth in Guangzhou, China (2001-2011)

BACKGROUND

Although effects of weather changes on human health have been widely reported, there is limited information regarding effects on pregnant women in developing countries.

OBJECTIVE

We investigated the association between maternal exposure to ambient temperature and the risk of preterm birth (< 37 weeks of gestation) in Guangzhou, China.

METHODS

We used a Cox proportional hazards model to estimate associations between preterm birth and average temperature during each week of gestation, with weekly temperature modeled as a time-varying exposure during four time windows: 1 week (the last week of the pregnancy), 4 weeks (the last 4 weeks of the pregnancy), late pregnancy (gestational week 20 onward), and the entire pregnancy. Information on singleton vaginal birth between 2001 and 2011 was collected. Daily meteorological data during the same period were obtained from the Guangzhou Meteorological Bureau.

RESULTS

A total of 838,146 singleton vaginal births were included, among which 47,209 (5.6%) were preterm births. High mean temperatures during the 4 weeks, late pregnancy, and the entire pregnancy time windows were associated with an increased risk of preterm birth. Compared with the median temperature (24.4°C), weekly exposures during the last 4 weeks of the pregnancy to extreme cold (7.6°C, the 1st percentile) and extreme heat (31.9°C, the 99th percentile) were associated with 17.9% (95% CI: 10.2, 26.2%) and 10.0% (95% CI: 2.9, 17.6%) increased risks of preterm birth, respectively. The association between extreme heat and preterm birth was stronger for preterm births during weeks 20-31 and 32-34 than those during weeks 35-36.

CONCLUSIONS

These findings might have important implications in preventing preterm birth in Guangzhou as well as other areas with similar weather conditions.

CITATION

He JR, Liu Y, Xia XY, Ma WJ, Lin HL, Kan HD, Lu JH, Feng Q, Mo WJ, Wang P, Xia HM, Qiu X, Muglia LJ. 2016. Ambient temperature and the risk of preterm birth in Guangzhou, China (2001-2011). Environ Health Perspect 124:1100-1106; http://dx.doi.org/10.1289/ehp.1509778.

A new birthweight reference in Guangzhou, southern China, and its comparison with the global reference

OBJECTIVE

To formulate a new birthweight reference for different gestational ages in Guangzhou, southern China, and compare it with the currently used reference in China and the global reference.

DESIGN AND SETTING

All singleton live births of more than 26 weeks' gestational age recorded in the Guangzhou Perinatal Health Care and Delivery Surveillance System for the years 2009, 2010 and 2011 (n=510 837) were retrospectively included in the study. In addition, the study sample was supplemented by all singleton live births (n=3538) at gestational ages 26-33 weeks from 2007 and 2008. We used Gaussian mixture models and robust regression to exclude outliers of birth weight and then applied Generalized Additive Models for Location, Scale, and Shape (GAMLSS) to generate smoothed percentile curves separately for gender and parity.

RESULTS

Of infants defined as small for gestational age (SGA) in the new reference, 15.3-47.7% (depending on gestational age) were considered appropriate for gestational age (AGA) by the currently used reference of China. Of the infants defined as SGA by the new reference, 9.2% with gestational ages 34-36 weeks and 14.3% with 37-41 weeks were considered AGA by the global reference. At the 50th centile line, the new reference curve was similar to that of the global reference for gestational ages 26-33 weeks and above the global reference for 34-40 weeks.

CONCLUSIONS

The new birthweight reference based on birthweight data for neonates in Guangzhou, China, differs from the reference currently used in China and the global reference, and appears to be more relevant to the local population.

No effect of embryo culture media on birthweight and length of newborns

STUDY QUESTION

Does the type of media used to culture embryos for IVF influence the birthweight and length of neonates?

SUMMARY ANSWER

No significant differences were observed in birthweight and length among the three embryo culture media used for in vitro embryo culture.

WHAT IS KNOWN ALREADY

Since the establishment of IVF as an assisted reproductive technology (ART), many different culture systems have been used for the development of human embryos. Some studies have shown that the types of culture media influence the newborn birthweight; however, other studies have shown no effect. To further explore this contradictory issue, we compared the birthweight and length of neonates born after the transfer of embryos cultured in one of three commercially available media.

STUDY DESIGN, SIZE AND DURATION

This retrospective analysis of birthweight and length of newborns included 1201 women who delivered singletons and 445 women who delivered twins. The following three commercially available culture media were used: G5™, Global and Quinn's advantage media. Women who underwent IVF-ET cycles between 2008 and 2010 were analyzed.

PARTICIPANTS/MATERIALS, SETTING AND METHODS

Patients younger than 40 years of age with a body mass index (BMI) <30 kg/m(2) were analyzed. Only data from singletons and twins born alive after the 20th week of gestation were included in the data analysis. Patients who received preimplantation genetic diagnosis (PGD) and donor oocytes were excluded.

MAIN RESULTS AND THE ROLE OF CHANCE

The analysis of 1201 singletons and 445 sets of twins showed no significant association between mean birthweight or mean birth length and the type of embryo culture medium. Inter-twin mean birthweight and length disparities were analyzed, but were not shown to be significantly different. Multiple linear regression analysis showed that maternal weight, maternal height, gestational age and infant gender were significantly related to birthweight, and paternal height, gestational age and newborn complications were significantly associated with birth length.

LIMITATIONS AND REASONS FOR CAUTION

The current study showed that birthweight and length of newborns were not associated with the embryo culture medium. More research needs to be performed to analyze the effects of other culture medium formulations and to evaluate the long-term effects of embryo culture medium on the health of children conceived through ART. WIDER IMPLICATIONS OF THESE FINDINGS: Our retrospective study suggests that embryo culture medium does not influence neonatal birthweight and length; however, the effects of culture medium on epigenetic variation of embryos need to be studied further.

Misclassification of newborns due to systematic error in plotting birth weight percentile values

OBJECTIVES

Higher than expected small for gestational age (SGA) rates and lower than expected large for gestational age (LGA) rates have been observed. A possible explanation is a leftward shift of percentile curves for birth weight due to a systematic error in plotting birth weight values in charts (ie, plotting weekly mean birth weight data at the beginning of the weeks). Our objectives were to assess how common this plotting error is and to analyze the effect of this error on SGA and LGA classification based on data from the German perinatal survey.

METHODS

First, a systematic literature search for birth weight charts was performed, and the charts were analyzed for the plotting error. Second, percentile values (10th, 50th, and 90th) for 25 to 42 completed weeks of gestation were calculated from the data of 1181200 male singleton newborns (German perinatal survey, 1995-2000). Birth weight percentile curves were calculated with and without the plotting error, and the resulting SGA and LGA rates were analyzed.

RESULTS

Fourteen of the 16 identified publications contained the systematic error in plotting. Using our calculated percentile curves, a leftward shift caused by the plotting error led to an SGA rate of 12.5% and an LGA rate of 7.7%; ∼5% of newborns were misclassified.

CONCLUSIONS

Percentile charts should be examined for the described systematic error and, if necessary, corrected.