JAMA：孕妇超重及肥胖与早产风险增加相关

　　据6月12日发表在《美国医学会杂志》上的一则研究披露，瑞典的一项包括了150万例的分娩案例研究指出，怀孕妇女在妊娠期间超重及肥胖与婴儿早产风险的增加有关，且与极端早产的最高风险有关。

　　根据文章的背景资料：“由于高流行率以及相关风险，怀孕妇女超重及肥胖已经在许多国家取代了吸烟而成为针对不良妊娠结果的最重要的可预防性风险因子。早产被定义为在妊娠达到37孕周前产下活婴，它是在非畸形婴儿中造成婴儿死亡、新生儿疾病及长期残疾的首要原因，而且死亡、患病和残疾的风险随着胎龄的变小而升高。”

　　瑞典斯德哥尔摩卡罗林斯卡医学院的Sven Cnattingius, M.D., Ph.D.及其同事开展了一项研究，旨在通过胎龄及通过早产前体来检查早期妊娠身体质量指数（BMI）与早产风险之间的关系。这项研究包括了从1992年至2010年间在瑞典生下活体单胎的妇女。怀孕妇女特征及其妊娠特征是从覆盖瑞典全国的瑞典医学出生登记记录中获取的。本研究主要检测的转归为早产风险（22-27周为极端早产；28-31周为严重早产；32-36周为中度早产）。这些转归被进一步地描绘为自发性（与早产宫缩或早产胎膜早破有关）及有医学指针的早产（在产程发动或诱导的产程发动之前进行剖腹产）。

　　BMI是根据首次产前就诊时的身高及体重资料进行计算的。BMI被用来描述妇女的体重，程度分别为过轻（BMI<18.5）、正常（18.5-<25）、过重（25-<30）、一级肥胖（30-<35）、二级肥胖（35-<40）或三级肥胖（≥40）。

　　在159万9551例具有早期妊娠BMI资讯的分娩案例中，有3082例为极端早产、6893例为严重早产、6万7059例为中度早产。研究人员发现，极端早产、严重早产和中度早产的风险会随着BMI的增加而升高，而与超重及肥胖相关的极端早产性风险是最高的。与正常体重妇女相比，二级及三级肥胖妇女（BMI≥35）的极端早产率会增加0.2%至0.3%，而严重早产率会增加0.3%至0.4%。

　　文章的作者得出结论：“鉴于在极端早产婴儿中的高疾病率和死亡率，即使是小幅的绝对风险差异都会对婴儿的健康与存活产生后果。即使美国的肥胖症流行看来已趋平稳，仍然还有相当多的妇女在开始怀孕时就具有相当高的BMI。鉴于其与公共卫生的潜在关系，我们的结果需要在其他人群中得到证实。还需要发现通过母体肥胖而影响后代健康的通路来提供特别针对具有最高早产风险妇女的关键信息。”

Maternal Obesity and Risk of Preterm Delivery
Importance
Preterm birth is a leading cause of infant mortality, morbidity, and long-term disability, and these risks increase with decreasing gestational age. Obesity increases the risk of preterm delivery, but the associations between overweight and obesity and subtypes of preterm delivery are not clear.
Objective
To study the associations between early pregnancy body mass index (BMI) and risk of preterm delivery by gestational age and by precursors of preterm delivery.
Design, Setting, and Participants
Population-based cohort study of women with live singleton births in Sweden from 1992 through 2010. Maternal and pregnancy characteristics were obtained from the nationwide Swedish Medical Birth Register.
Main Outcomes and Measures
Risks of preterm deliveries (extremely, 22-27 weeks; very, 28-31 weeks; and moderately, 32-36 weeks). These outcomes were further characterized as spontaneous (related to preterm contractions or preterm premature rupture of membranes) and medically indicated preterm delivery (cesarean delivery before onset of labor or induced onset of labor). Risk estimates were adjusted for maternal age, parity, smoking, education, height, mother's country of birth, and year of delivery.
Results
Among 1 599 551 deliveries with information on early pregnancy BMI, 3082 were extremely preterm, 6893 were very preterm, and 67 059 were moderately preterm. Risks of extremely, very, and moderately preterm deliveries increased with BMI and the overweight and obesity-related risks were highest for extremely preterm delivery. Among normal-weight women (BMI 18.5-<25), the rate of extremely preterm delivery was 0.17%. As compared with normal-weight women, rates (%) and adjusted odds ratios (ORs [95% CIs]) of extremely preterm delivery were as follows: BMI 25 to less than 30 (0.21%; OR, 1.26; 95% CI, 1.15-1.37), BMI 30 to less than 35 (0.27%; OR, 1.58; 95% CI, 1.39-1.79), BMI 35 to less than 40 (0.35%; OR, 2.01; 95% CI, 1.66-2.45), and BMI of 40 or greater (0.52%; OR, 2.99; 95% CI, 2.28-3.92). Risk of spontaneous extremely preterm delivery increased with BMI among obese women (BMI≥30). Risks of medically indicated preterm deliveries increased with BMI among overweight and obese women.
Conclusions and Relevance
In Sweden, maternal overweight and obesity during pregnancy were associated with increased risks of preterm delivery, especially extremely preterm delivery. These associations should be assessed in other populations.