Background: There has been no large nationwide population-based study to examine the effects of maternal smoking status during pregnancy on birth weight that simultaneously controlled for clinical information, socioeconomic status, and maternal weight. Thus, this study aimed to determine the association between maternal smoking status during pregnancy and birth weight, while taking these confounding factors into consideration.
Methods: This study examined the first-year fixed dataset from a large nationwide birth cohort study that commenced in 2011. The dataset consisted of information on 9369 singleton infants born before December 31, 2011. Children were divided into 4 groups for statistical analysis: those born to mothers who did not smoke (NS), who quit smoking before pregnancy, who quit smoking during early pregnancy, and who smoked (SM). Multiple linear regression models were conducted for each sex to examine the association between maternal smoking status during early pregnancy and fetal growth. Birth weight was estimated using the least-squares method after controlling for covariates.
Results: After controlling for potential confounding factors, maternal smoking status during pregnancy was significantly associated with birth weight. There was a significant difference in birth weight between NS and SM for both male and female infants (male infants, 3096.2 g [NS] vs 2959.8 g [SM], P < 0.001; female infants, 3018.2 g [NS] vs 2893.7 g [SM], P < 0.001).
Conclusions: Using data from a large nationwide birth cohort study in Japan, we have shown that maternal smoking during pregnancy may reduce birth weight by 125-136 g.
背景：: 妊娠中の喫煙が出生体重に与える影響について、臨床情報や社会経済的状況、さらには母体の体重を同時に考慮した全国規模の研究はほとんどない。そこで、この研究ではこれらの交絡因子を考慮したうえで、妊娠中の喫煙と出生体重の関連を検討することを目的とした。
方法：: 2011年に開始された日本を代表する大規模な出生コホート研究の、当初1年分の固定データを用いて解析を行った。このデータは2011年12月31日以前に、単胎として出生した9369人の情報を含む。これらの出生児は母親の喫煙状況により、「喫煙なし（NS）」「妊娠前に禁煙」「妊娠初期に禁煙」「喫煙あり（SM）」の4群に分類された。男女別の重回帰モデルにより、妊娠中の喫煙と胎児の発育についての関連を検討した。最小2乗法により共変量を調整した調整後出生体重を推定した。
結果：: 交絡因子を調整した結果、妊娠中の喫煙は男児、女児とも出生体重と有意に関連していた。NS群とSM群における出生体重には有意な差が存在した（男児：3096.2 g (NS) vs. 2959.8 g (SM) [p < 0.001]; 女児：3018.2 g (NS) vs. 2893.7 g (SM) [p < 0.001]）。
結論：: 日本において全国規模の出生コホート研究のデータを用いて、妊娠中の喫煙が出生体重を125—136g減少させる可能性を示した。