Centre for Economic Demography, Unit for Social Epidemiology, Department of Clinical Sciences, Faculty of Medicine, Lund University, Lund, Sweden.
PLoS One. 2013 Apr 17;8(4):e61734. doi: 10.1371/journal.pone.0061734. Print 2013.
Maternal smoking during pregnancy (SDP) seems associated with reduced birthweight in the offspring. This observation, however, is based on conventional epidemiological analyses, and it might be confounded by unobserved maternal characteristics related to both smoking habits and offspring birth weight. Therefore, we apply a quasi-experimental sibling analysis to revisit previous findings. Using the Swedish Medical Birth Register, we identified 677,922 singletons born between 2002 and 2010 from native Swedish mothers. From this population, we isolated 62,941 siblings from 28,768 mothers with discrepant habits of SDP. We applied conventional and mother-specific multilevel linear regression models to investigate the association between maternal SDP and offspring birthweight. Depending on the mother was light or heavy smoker and the timing of exposition during pregnancy (i.e., first or third trimester), the effect of smoking on birthweight reduction was between 6 and 78 g less marked in the sibling analysis than in the conventional analysis. Sibling analysis showed that continuous smoking reduces birthweight by 162 grams for mothers who were light smokers (1 to 9 cigarettes per day) and 226 g on average for those who were heavy smokers throughout the pregnancy in comparison to non-smoker mothers. Quitting smoking during pregnancy partly counteracted the smoking-related birthweight reduction by 1 to 29 g, and a subsequent smoking relapse during pregnancy reduced birthweight by 77 to 83 g. The sibling analysis provides strong evidence that maternal SDP reduces offspring birthweight, though this reduction was not as great as that observed in the conventional analysis. Our findings support public health interventions aimed to prevent SDP and to persuade those who already smoke to quit and not relapse throughout the pregnancy. Besides, further analyses are needed in order to explain the mechanisms through which smoking reduces birthweight and to identify other maternal characteristics that are common causes of both birthweight reduction and maternal smoking.
孕妇吸烟（SDP）似乎与后代出生体重降低有关。然而，这一观察结果是基于传统的流行病学分析得出的，可能受到与吸烟习惯和后代出生体重相关的未观察到的母体特征的混杂。因此，我们应用准实验性同胞分析来重新审视先前的发现。我们利用瑞典医学出生登记处，确定了 2002 年至 2010 年间出生的 677922 名瑞典籍母亲所生的单胎婴儿。从这一人群中，我们从 28768 名母亲中分离出了 62941 对有差异 SDP 习惯的同胞。我们应用传统和母亲特异性多水平线性回归模型来研究 SDP 与后代出生体重之间的关联。根据母亲是轻度吸烟者还是重度吸烟者以及怀孕期间暴露的时间（即第一或第三孕期），同胞分析中吸烟对出生体重减轻的影响比传统分析中要小 6 到 78 克。同胞分析表明，与不吸烟者相比，轻度吸烟者（每天 1 至 9 支香烟）的母亲持续吸烟会使出生体重降低 162 克，而整个孕期重度吸烟者的平均出生体重降低 226 克。怀孕期间戒烟会部分抵消与吸烟相关的出生体重减轻 1 至 29 克，而怀孕期间再次吸烟会使出生体重降低 77 至 83 克。同胞分析提供了强有力的证据表明，孕妇吸烟会降低后代的出生体重，尽管这种降低程度不如传统分析观察到的那样大。我们的研究结果支持旨在预防 SDP 的公共卫生干预措施，并说服那些已经吸烟的人戒烟并在整个孕期不复发。此外，还需要进一步分析以解释吸烟如何降低出生体重的机制，并确定其他共同导致出生体重降低和母亲吸烟的母体特征。
