Lawlor Debbie A, Clark Heather, Smith George Davey, Leon David A
Department of Social Medicine, University of Bristol, Bristol, United Kingdom.
Pediatrics. 2006 May;117(5):e894-902. doi: 10.1542/peds.2005-2412.
The objective of this study was to examine whether the established positive association between birth weight and childhood psychometric intelligence is seen within singleton sibling pairs from the same family as well as between nonsiblings.
We examined the association of intrauterine growth (measured as birth weight standardized for gender and gestational age) with psychometric intelligence (measured using the Moray House picture test) at 7 years old in a birth cohort of 9792 individuals who were singleton births occurring in Aberdeen, Scotland, between 1950 and 1956. We further compared this association within siblings with that between nonsiblings in the cohort; this family-based analysis included 1645 sibling pairs (N = 3290 individuals).
There was a positive linear association between birth weight and childhood psychometric intelligence at age 7 in the whole cohort, which remained with adjustment for a range of potential confounding factors. A one standard deviation increase in birth weight for gestational age z score was associated with a greater intelligence score in a regression model adjusting for sex, year of birth, paternal social class, maternal height, age, gravidity, and birth outside of marriage. The mean age difference between the siblings within each family pair was 2.2 years. In the family-based analysis there was no strong association between birth weight for gestation age z score and intelligence within sibling pairs from the same family, but there was a positive association between nonsiblings; the difference in these effects being unlikely to be due to chance. With additional adjustment for social class, maternal height, age, gravidity, and birth outside of marriage, the within-sibling pair effect was unaltered and the nonsibling effect attenuated, although an apparently robust positive association remained. In these adjusted analyses there was still evidence that the within-sibling effect differed from that between nonsiblings. We found no evidence that the main effects or the family-based analyses differed between males and females.
Our family-based analyses are consistent with one previous large family-based study that included >2500 sibling pairs and found no within-sibling-pairs association between birth weight and childhood intelligence, but did not make a direct statistical comparison between the within-sibling-pairs association and that between nonsiblings. In a second large study that included only sibling pairs of the same sex, in males there was a within-sibling-pairs association between birth weight and childhood intelligence. However, for females there was no within-sibling-pairs association. The authors commented that this sex difference was puzzling and needed replication. Although we had less power than this earlier study to assess sex differences, the point estimates and statistical tests in our study suggested that there was no sex difference.
The lack of any association within sibling pairs from the same family suggests that the association between birth weight and childhood intelligence in the general population of singletons is largely explained by fixed family factors that are closely matched in siblings of a similar age. These factors include family socioeconomic characteristics, parental education and intelligence, genetic factors and fixed maternal factors, such as her behaviors, size, and metabolic and cardiovascular health that are constant from one pregnancy to the next and could therefore affect her offspring growth and intelligence across all pregnancies.
本研究的目的是检验出生体重与儿童心理测量智力之间已确立的正相关关系，在来自同一家庭的单胎同胞对以及非同胞个体之间是否也成立。
我们在一个由9792名个体组成的出生队列中，研究了子宫内生长情况（以根据性别和孕周标准化的出生体重衡量）与7岁时心理测量智力（使用莫雷豪斯图片测验测量）之间的关联。这些个体是1950年至1956年间在苏格兰阿伯丁出生的单胎。我们进一步比较了该队列中同胞对之间以及非同胞个体之间的这种关联；这种基于家庭的分析包括1645对同胞（N = 3290人）。
在整个队列中，出生体重与7岁时儿童心理测量智力之间存在正线性关联，在对一系列潜在混杂因素进行调整后该关联依然存在。在一个对性别、出生年份、父亲社会阶层、母亲身高、年龄、妊娠次数和非婚生育进行调整的回归模型中，孕周z评分的出生体重每增加一个标准差，智力得分就会更高。每个家庭对中同胞之间的平均年龄差为2.2岁。在基于家庭的分析中，同一家族同胞对中孕周z评分的出生体重与智力之间没有强关联，但非同胞个体之间存在正相关；这些效应的差异不太可能是偶然的。在进一步对社会阶层，并对母亲身高、年龄、妊娠次数和非婚生育进行调整后，同胞对内部效应未改变，非同胞效应减弱，尽管仍存在明显稳健的正相关。在这些调整后的分析中，仍有证据表明同胞对内部效应与非同胞个体之间的效应不同。我们没有发现证据表明主要效应或基于家庭的分析在男性和女性之间存在差异。
我们基于家庭的分析与之前一项大型基于家庭的研究一致，该研究包括>2500对同胞对，发现同胞对内部出生体重与儿童智力之间没有关联，但没有对同胞对内部关联与非同胞个体之间的关联进行直接统计比较。在另一项大型研究中，该研究仅包括同性别的同胞对，在男性中，出生体重与儿童智力之间存在同胞对内部关联。然而，对于女性来说，同胞对内部没有关联。作者评论说这种性别差异令人困惑，需要重复验证。尽管我们评估性别差异的能力比早期这项研究弱，但我们研究中的点估计和统计检验表明没有性别差异。
来自同一家庭的同胞对之间缺乏任何关联表明，在单胎总体人群中出生体重与儿童智力之间的关联很大程度上是由固定的家庭因素所解释的，这些因素在年龄相近的同胞中密切匹配。这些因素包括家庭社会经济特征、父母教育程度和智力、遗传因素以及固定的母亲因素，例如她的行为、体型以及代谢和心血管健康状况，这些在每次怀孕时都是恒定的，因此可能会影响她所有怀孕后代的生长和智力。
