Factors influencing the relationship between a newborn assessment of gestational maturity and the gestational age interval

This study examines the correlation and agreement between the calculated 'gestational interval' from the date of last menstrual period (LMP) and the Ballard newborn assessment of gestational maturity. It then investigates selected maternal socio-demographic, prenatal, intrapartum and infant factors which may account for differences between these two gestational age determination methods. Single live-born deliveries (n = 10,794) were selected from a 1982-1986 medical university perinatal information data system for analysis. The Ballard assessment overestimates the LMP at earlier gestational ages and underestimates in the post-term range. The discrepancy between LMP and Ballard varies across the range of gestational age values and the extent of variation differs by several maternal and infant risk factors. These findings suggest considerable bias may result from the indiscriminate case mixing of LMP and Ballard values for use in gestational age research or in standardising developmental tests. We highlight the deficiencies in using correlation coefficients or mean differences to assess agreement between these measures.     

Ethnic variation in postnatal assessments of gestational age: a reappraisal

While the possibility of an ethnic bias in postnatal assessments of gestational age has been suggested by several investigators, others have reported that postnatal assessments do not provide biased estimates in non-White ethnic groups. In the light of this ongoing controversy, this study examines the validity of the Ballard postnatal assessment of gestational age by ethnicity, using a relatively large hospital data base that allows for the inspection of ethnic variations in the agreement between the Ballard assessment and last menstrual period (LMP). The results indicate that there is a greater over-estimation of the LMP interval by the Ballard method in Blacks compared with Whites and suggest that systematic differences exist by ethnicity of mother in the agreement between the Ballard postnatal assessment and the LMP interval. After taking maternal characteristics and pregnancy complications into account, for a given gestational age interval, Blacks have on average a greater level of maturity as measured by Ballard. One interpretation of these findings is that postnatal assessments may provide biased over-estimates of the LMP gestational age interval in certain ethnic groups. An alternative interpretation of these data is that the gestational age interval based on LMP is not a valid indicator of fetal maturity, readiness for birth and infant risk status across all ethnic groups.     

Variation between last-menstrual-period and clinical estimates of gestational age in vital records

An accurate assessment of gestational age is vital to population-based research and surveillance in maternal and infant health. However, the quality of gestational age measurements derived from birth certificates has been in question. Using the 2002 US public-use natality file, the authors examined the agreement between estimates of gestational age based on the last menstrual period (LMP) and clinical estimates in vital records across durations of gestation and US states and explored reasons for disagreement. Agreement between the LMP and the clinical estimate of gestational age varied substantially across gestations and among states. Preterm births were more likely than term births to have disagreement between the two estimates. Maternal age, maternal education, initiation of prenatal care, order of livebirth, and use of ultrasound had significant independent effects on the disagreement between the two measures, regardless of gestational age, but these factors made little difference in the magnitude of gestational age group differences. Information available on birth certificates was not sufficient to understand this disparity. The lowest agreement between the LMP and the clinical estimate was observed among preterm infants born at 28-36 weeks' gestation, who accounted for more than 90% of total preterm births. This finding deserves particular attention and further investigation.     

Comparison of gestational age at birth based on last menstrual period and ultrasound during the first trimester

Reported last menstrual period (LMP) is commonly used to estimate gestational age (GA) but may be unreliable. Ultrasound in the first trimester is generally considered a highly accurate method of pregnancy dating. The authors compared first trimester report of LMP and first trimester ultrasound for estimating GA at birth and examined whether disagreement between estimates varied by maternal and infant characteristics. Analyses included 1867 singleton livebirths to women enrolled in a prospective pregnancy cohort. The authors computed the difference between LMP and ultrasound GA estimates (GA difference) and examined the proportion of births within categories of GA difference stratified by maternal and infant characteristics. The proportion of births classified as preterm, term and post‐term by pregnancy dating methods was also examined. LMP‐based estimates were 0.8 days (standard deviation = 8.0, median = 0) longer on average than ultrasound estimates. LMP classified more births as post‐term than ultrasound (4.0% vs. 0.7%). GA difference was greater among young women, non‐Hispanic Black and Hispanic women, women of non‐optimal body weight and mothers of low‐birthweight infants. Results indicate first trimester report of LMP reasonably approximates gestational age obtained from first trimester ultrasound, but the degree of discrepancy between estimates varies by important maternal characteristics.     

Determining Gestational Age in a Low-resource Setting: Validity of Last Menstrual Period

The validity of three methods (last menstrual period [LPM], Ballard and Dubowitz scores) for assessment of gestational age for premature infants in a low-resource setting was assessed, using antenatal ultrasound as the gold standard. It was hypothesized that LMP and other methods would perform similarly in determining postnatal gestational age. Concordance analysis was applied to data on 355 neonates of <33 weeks gestational age enrolled in a topical skin-therapy trial in a tertiary-care children''s hospital in Bangladesh. The concordance coefficient for LMP, Ballard, and Dubowitz was 0.878, 0.914, and 0.886 respectively. LMP and Ballard underestimated gestational age by one day (±11) and 2.9 days (±7.8) respectively while Dubowitz overestimated gestational age by 3.9 days (±7.1) compared to ultrasound finding. LMP in a low-resource setting was a more reliable measure of gestational age than previously thought for estimation of postnatal gestational age of preterm infants. Ballard and Dubowitz scores are slightly more reliable but require more technical skills to perform. Additional prospective trials are warranted to examine LMP against antenatal ultrasound for primary assessment of neonatal gestational age in other low-resource settings.Key words: Gestational age, Last menstrual period, Neonatal health, Obstetrics, Bangladesh     

United States vital statistics and the measurement of gestational age

Estimates of the gestational age of the newborn based on US Birth Certificate data are extensively used to monitor trends in infant and maternal health and to improve our understanding of adverse pregnancy outcome. Two measures of gestational age, the 'date of the last normal menses' (LMP) and the 'clinical estimate of gestation' (CE), have been available from birth certificate data since 1989. Reporting irregularities with the LMP-based measure are well-documented, and important questions remain regarding the derivation of the CE. Changes in perinatal medicine and in vital statistics reporting in recent years may have importantly altered gestational age data based on vital statistics. This study describes how gestational age measures are collected and edited in US national vital statistics, and examines changes in the reporting of these measures by race and Hispanic origin between 1990 and 2002. Data are drawn from the National Center for Health Statistics' restricted use US birth files for 1990–2002. Bivariable statistics are used.
The percentage of records with missing LMP dates declined markedly over the study period, overall, and for each racial/Hispanic origin group studied. A marked shift in the distribution of the CE of gestational age was also observed, suggesting changes both in the true distribution of age at birth, and in the derivation of this measure. Agreement between the LMP-based and CE estimates increased over the study period, especially among preterm births. However, a high proportion of LMP dates continue to be missing or invalid and the derivation of the CE is still uncertain. In sum, although the reporting of gestational age measures in vital statistics appears to have improved between 1990 and 2002, substantial concerns with both the LMP-based and the CE persist. Efforts to identify approaches to further improve upon the quality of these data are needed.     

小于胎龄儿发病相关危险因素分析

【目的】分析小于胎龄(small for gestational age,SGA)儿发病的相关危险因素,为临床防治提供参考。【方法】采用1∶2配对的病例对照研究方法,选取本院2005年1月～2006年12月出生的240例单胎活产SGA儿及同期出生的相同胎龄的适于胎龄儿(appropriate for gestational age,AGA)480例,应用Logistic回归分析方法,对其影响因素进行分析。【结果】多元回归分析显示:妊娠高血压综合症、既往异常妊娠史、母亲文化程度低、孕期被动吸烟与SGA发生有关联,其OR值分别为5.65、2.83、3.53、4.71。【结论】妊娠高血压综合症、既往异常妊娠史、母亲文化程度低、孕期被动吸烟,是SGA发生的危险因素,应从孕期保健做起,避免或减少SGA的发生。     

孕产妇暴露因素与小于胎龄儿关系的研究现状

本文通过文献研究,简述了孕产妇暴露因素与小于胎龄儿（SGA）的国内外的研究现状,分析并总结了SGA的结局及其与孕产妇暴露因素之间的关系,为降低SGA的发生、实现优生优育提供重要指导和参考。     

Racial differences in birthweight for gestational age and infant mortality in extremely-low-risk US populations

Using national data, we develop and contrast the birth-weight percentiles for gestational age by infants of extremely-low-risk (ELR) White and African-American women and examine racial differences in the proportion of small-for-gestational-age (SGA) births. We then scrutinise racial variations in infant mortality rates of the infants of ELR women. We further compare the infant mortality rates of infants at or below the 10th percentile of birthweight for gestational age of each race group to determine whether infants with similar restricted fetal growth have comparable risks of subsequent mortality. Single live births, 34-42 weeks' gestation, to White and African-American US-resident mothers were selected from the 1990-91 US Linked Live Birth--Infant Death File (n = 4,360,829). Extremely-low-risk mothers were defined as: married, aged 20-34 years, 13+ years of education, multiparae, with average parity for age, adequate prenatal care, vaginal delivery, and no reports of medical risk factors, tobacco use or alcohol use during pregnancy. Marked racial variation in birthweight percentiles by gestational age was evident. Compared with ELR White mothers, the risk of an SGA infant was 2.64 times greater for ELR African-American mothers and the risk of infant mortality was 1.61 times greater. For the ELR group, the infant mortality rates of African-American and White infants at or below the 10th percentile of birthweight for gestational age of their respective maternal race group were essentially identical after controlling for gestational age. In conclusion, race differences in fetal growth patterns remained after controlling for risk status. Efforts to remove racial disparities in infant mortality will need to develop aetiological pathways that can explain why African-Americans have relatively higher rates of preterm birth and higher infant mortality rates among term and non-SGA infants.     

Comparison of gestational age classifications: date of last menstrual period vs. clinical estimate

PURPOSE: The purpose was to compare the two different measures of gestational age currently used on birth certificates (the duration of pregnancy based on the date of last menstrual period [LMP] and the clinical estimate [CE] as related to health status indicators. We contrasted these measures by race/ethnicity. METHODS: NCHS natality files for 2000-2002 were used, selecting cases of single live birth to U.S. resident mothers with both LMP and CE gestational age information. RESULTS: Approximately 75% of the records had valid LMP and CE values and for approximately one-half of these, the LMP and CE values did not exactly agree. Overall and for each race and ethnic group, the LMP measures resulted in higher proportions of very preterm, preterm, postterm and SGA births. CE value provided preterm rates of 7.9% and for LMP, 9.9%. The odds ratio of preterm birth for African-Americans using the CE measure was 1.78 [95% Cl 1.77-1.79]. The odds ratio using LMP was 1.93 [95% Cl 1.92-1.94]. Whites were the referent population. CONCLUSIONS: Different measures of gestational age result in different overall and race-specific rates of very preterm, preterm, postterm, and SGA births. These findings indicate that substituting or combining these measures may have consequences.     

The use of covariates to identify records with implausible gestational ages using the birthweight distribution

Parker JD, Liao D, Schenker N, Branum A. The use of covariates to identify records with implausible gestational ages using the birthweight distribution. Paediatric and Perinatal Epidemiology 2010. The objective of this study was to evaluate the usefulness of covariates in identifying birth records with implausible values of gestational age. Birthweight distributions for births with early reported gestational ages are markedly bimodal, suggesting a mixture of two distributions. Most births form a normal‐shaped left‐hand (primary) distribution and a smaller number form the right‐hand (secondary) distribution. The births in the secondary distribution are thought to have gestational age mistakenly reported. Prior work has found that births in the secondary distribution are at higher risk of poor outcomes than those in the primary distribution. Using 2002 US Natality data for gestational ages 26–35 weeks, we fit normal mixture models to birthweight with and without covariates (maternal race, education, parity, age, region of the country, prenatal care initiation) by reported gestational age. Additional models were stratified by infant sex. This approach allowed for the relationship between the covariates and birthweight to differ between the components. Mixture models fit reasonably well for reported gestational ages <33 weeks, but not for later weeks. Counter to the hypothesis, results were similar for models with and without covariates or stratification or both, although stratified models without covariates predicted slightly more girls and slightly fewer boys in the secondary distribution than did the corresponding unstratified models. For reported gestational ages <33 weeks, predictions from the four sets of models were highly correlated and predictions were similar for subgroups defined by the clinical estimates of gestational age and other covariates. For births with reported gestational ages of 29 or more weeks, the proportion in the secondary distribution exceeded 30%, although this varied by maternal characteristics. The use of covariates and stratification complicated model fitting without materially improving identification of implausible gestational age values, supporting inferences from prior studies using data ‘cleaned’ without consideration of maternal or infant characteristics.     

The research implications of the selection of a gestational age estimation method

There are three primary methods of gestational age estimation: dating based on last menstrual period (LMP), ultrasound-based dating and neonatal estimates. We review the strengths and limitations of each method as well as their implications for research. Dating based on LMP is a simple, low-cost method of estimating gestational age. Limitations associated with the use of menstrual-based dating include reporting problems such as uncertainty regarding the LMP date, possibly due to bleeding not associated with menses, as well as concerns about the incidence of delayed ovulation, which can result in invalid estimates of gestation, even for women with certain LMP dates. Given that most women in the US have at least one ultrasound during pregnancy, it is becoming increasingly common for clinicians to verify menstrual dates using early ultrasound. To calculate gestational age with the use of ultrasound, fetal measurements are compared with a gestational age-specific reference. The primary limitation of this method is the fact that the gestational age estimates of symmetrically large or small fetuses will be biased. Further, given that ultrasound references were developed using pregnancies that were dated according to reliable LMP dates, they are potentially biased in the same direction as dates calculated according to LMP. Neonatal estimates of gestational age have been shown to be the least precise dating method. To highlight the research implications of the choice of a gestational dating method, we used data from the Routine Antenatal Diagnostic Imaging with Ultrasound Study to identify risk factors for post-term delivery. Risk factors for post-term delivery are shown to vary according to the choice of a gestational dating method, suggesting that some findings are an artefact of the choice of a method rather than evidence of causality.     

Agreement between maternal interview- and medical record-based gestational age.

Agreement between maternal interview- and medical record-based gestational age was assessed by using data from a case-control study of childhood strabismus. The sample consisted of 383 cases of strabismus and their age-matched controls, diagnosed between 1985 and 1986 in Baltimore, Maryland, who were under age 7 years when diagnosed. Medical record-based gestational age was derived, in order of priority, from early ultrasound examination, time from the last menstrual period, pediatric examination, and obstetric examination. The intraclass correlation coefficient, kappa, and mean difference were used to compare agreement between maternal interview- and medical record-based gestational age by maternal and pregnancy characteristics and characteristics related to study design. Overall, 86 percent of mothers were within 2 weeks of the gestational age reported in the medical record. The intraclass correlation coefficient comparing maternal and medical record-based gestational age was 0.83 (95% confidence interval 0.80-0.86). Agreement was positively associated with shorter length of recall, low birth order, and having a neonatal illness related to prematurity. Agreement was poor among mothers of healthy preterm infants. There was a weak positive association between recall and some sociodemographic covariates. There was greater misclassification of prematurity in the controls than in the cases. The results suggest that, in general, women recall gestational age well, which supports the use of gestational age derived from maternal interviews.     

出生胎龄与小于胎龄儿智能发育的相关性分析

目的 分析出生胎龄与小于胎龄儿(SGA)智能发育的相关性,为SGA的管理和早期干预提供参考。方法 采用回顾性病例对照方式将纳入研究的SGA按出生胎龄分为早期早产儿(<32周)、中期早产儿(32~33^+6周)、晚期早产儿(34~36^+6周)、早期儿(37~38^+6周)和足月儿(≥39周)5个组,应用0~6岁小儿神经心理发育量表对纳入研究的SGA进行智能发育评估。组间比较采用方差分析、Kruskal-Wallis检验、卡方检验和Fisher精确检验,胎龄与智能发育水平的相关性采用多元回归模型、曲线拟合以及阈值效应分析。结果 本研究共纳入研究对象203例。调整了可能的混杂因素后,早期儿组SGA较早期早产儿组SGA发育商得分高23.06分(95%置信区间[confidence interval,CI],12.58-33.55;P<0.01),较中期早产儿组SGA高7.03分(95%CI:0.74-13.32;P<0.05),较晚期早产儿组SGA高5.2分(95%CI:0.91-9.49;P<0.05),较足月儿组SGA高6.08分(95%CI:1.19-10.98;P<0.05)。阈值效应分析发现出生胎龄的关键时间点为37周,当出生胎龄<37周时,胎龄每增加1周SGA的发育商得分提高2.29分(95%CI:1.07-3.52,P<0.01);当出生胎龄>37周时,胎龄每增加1周SGA的发育商得分降低2.14分(95%CI:0.11-4.17,P<0.05)。结论 SGA智能发育水平与出生胎龄呈"U"型相关,在SGA的随访管理中应当将早产和足月SGA作为重点监测人群。     

Premature or Just Small? Training Guatemalan Birth Attendants to Weigh and Assess Gestational Age of Newborns: An Analysis of Outcomes

We describe Guatemalan birth attendants’ identification of vulnerable newborns, their evaluation of gestational age and anthropometry, and the validity of the Capurro and New Ballard newborn gestational age assessment methods. We interviewed 49 birth attendants and trained 10 of these women to assess 63 newborns. The Capurro and Ballard methods were correlated (Spearman rho = .75, p < .001) and showed agreement (Bland-Altman plot, difference and bias, ?0.33 ± 1.3 weeks). Prematurity was estimated at 27% (Ballard) and 24% (Capurro); low birth weight (LBW) was 30%. Capurro provided a simplified, equivalent estimate of gestational age compared with New Ballard that could be used by birth attendants.     

妊高征与小于胎龄儿的相关性研究

目的:探讨妊高征与小于胎龄儿(SGA)之间的联系。方法:选取2000年1月~2004年10月在本院出生的单胎活产SGA病例共834例(男443例,女391例)作为病例组。以胎儿性别及出生孕周进行频数匹配,按1∶3的比例,采用完全随机抽样方法选取出生体重在10%~90%分位的适于胎龄儿2 502例(男1 329例,女1 173例)为对照组,比较病例组及对照组新生儿母亲孕期患妊高征的比例。结果:①病例组母亲患轻度、中度及重度妊高征比例分别是对照组的2.52(95%C I,1.35~4.69)、4.21(2.03~8.70)和5.15(3.10~8.54)倍;②分层分析表明,男性及女性病例组母亲妊高征的患病比例分别是对照组的4.45(2.72~7.27)和3.51(2.14~5.75)倍,男性及女性病例组母亲妊高征的患病优势比无显著差异,早产和足月病例组母亲患妊高征的比例分别为对照组的9.96(4.50~22.02)和3.21(2.15~4.78)倍,早产病例组母亲妊高征的患病优势比显著高于足月病例组;③校正性别、足月与否及母亲年龄的多因素分析结果与单因素分析结果类似。结论:妊高征可显著增加SGA发病的危险性。     

Implications of cleaning gestational age data

Gestational age is an important birth characteristic examined in epidemiological studies. Though there are well-documented problems with the reporting of gestational age on birth certificates, schemes for addressing this issue have not been systematically evaluated. With singleton births from the 1995-97 US linked birth/infant death files, we compared a handful of perinatal outcome estimates derived from the resulting analytical files using two published methods often used to manage inconsistent gestational age data. The first method (Alexander et al., 1996), provides cut-points for implausible birthweight-gestational age combinations and excludes infants with birthweights outside a plausible range. The second (Zhang and Bowes, 1995), provides different cut-points for implausible birthweight-gestational age combinations and then substitutes the clinical gestational age estimate for the original value, if available, reducing the number of births at the affected gestational age, but excluding fewer births from the resulting analytical files. The Alexander method excluded 0.4 of our study population and the Zhang method reassigned and excluded 1.0 and 0.2, respectively; however, over 20 of birth records with gestational age 28-30 weeks were modified by either method. Using either method, more high-risk than low-risk and more black than white births were excluded. These differential exclusions affected corresponding perinatal outcome estimates and relative risks between maternal risk groups for preterm delivery, gestation-specific infant mortality and birthweight; overall infant mortality rates were not affected. Systematic comparisons between results of different studies will need to consider the data modifications used, the populations affected, and the outcomes assessed when drawing conclusions.     

孕周别体重和体质指数分析

目的 建立孕周别体重和体质指数（BMI）参考值范围,探讨其孕期变化规律. 方法 对2009年6月—2011年5月在北京市顺义区医院和顺义区妇幼保健院进行第1次产前检查（9周≤孕周＜14周）的孕妇进行间隔为5（±1）周的定期随访至分娩,采用偏度-中位数-变异系数法修匀其孕期体重和BMI百分位数,并探讨其每周环比增长规律. 结果 获得顺义区孕周别体重和BMI修匀百分位数,二者随孕周增加呈现直线增长的趋势,孕期体重和BMI每周环比增长曲线变化规律相似,均在13周时开始上升,24周后缓慢下降,32 ～38周平稳,体重每周环比增长曲线38周之后又缓慢升高,BMI则保持平坦. 结论 本研究建立了北京市顺义区孕周别体重和BMI百分位数修匀曲线,可为该地区及其它类似地区的孕妇孕期增重和营养评价提供新的参考依据.     

Social determinants of infant mortality in a historical Swedish cohort

Background: Infant mortality rates have fallen considerably in the past decades. However, because of sparseness of historical data, it is unclear how social differences in infant mortality have changed over time. Methods: The aim of this study was to assess the association between prenatal social determinants and infant mortality in a Swedish cohort of 13 741 singletons born between 1915 and 1929. Associations and potential mediation of these determinants through other maternal and birth factors were studied using Cox regression. Analyses were repeated for deaths within the neonatal and post‐neonatal periods. Results: Mother's single marital status, high parity, low birthweight (LBW), low gestational age and male sex were associated with infant mortality in fully adjusted models, whereas the associations of maternal social class, region of residence and maternal age appeared to be largely mediated through other variables. Contrary to studies reporting a ‘LBW paradox’, no interactions between gestational age or birthweight and maternal social characteristics on infant mortality were observed in this study. High maternal age, LBW and low/high gestational age were associated with neonatal mortality, whereas single marital status, high parity, LBW, low gestational age and male sex were associated with post‐neonatal mortality. An association of family social class with post‐neonatal mortality was largely mediated by other maternal variables. Conclusions: Our findings of determinants of neonatal and post‐neonatal mortality in 1915–1929 are strikingly consistent with results from contemporary cohorts. On the other hand, contrary to most recent findings, there is no evidence of a LBW paradox in this historical cohort.     

Relationship between newborn size and mother's blood cadmium levels, Toyama, Japan

The effect of blood cadmium (Cd), which reflects not only Cd body burden but also recent Cd exposure and communicates with fetal blood in the placenta, on newborn size at birth was investigated. Blood Cd of 55 mothers from Toyama, Japan, at 30-32 gestational weeks was measured using a flameless atomic absorption spectrophotometer. The relationship between blood Cd and newborn size was analyzed after adjustment for gestational age and maternal build. A significant inverse correlation was found between infant height and maternal blood Cd. After adjustment for gestational age and maternal weight at 30-32 gestational weeks, the significant inverse relationship between maternal blood Cd and infant height was shown using the multiple regression analysis. Newborn size might be influenced by maternal blood Cd levels to which infants may be exposed during gestation.