Department of Epidemiology and Biostatistics, Michigan State University, East Lansing, MI; Department of Pediatrics and Human Development, Michigan State University, East Lansing, MI.
Section of Endocrinology, Diabetes, Nutrition and Weight Management, Department of Medicine, Boston University School of Medicine, Boston, MA.
Am J Obstet Gynecol. 2021 Jan;224(1):82.e1-82.e8. doi: 10.1016/j.ajog.2020.06.052. Epub 2020 Jul 9.
US iodine intake, estimated from the median urinary iodine concentration of population representative data, has declined by half since the 1970s, which is problematic because maternal iodine intake is critical for fetal neurodevelopment. Relying on median urinary concentrations to assess iodine intake of populations is standard practice but does not describe the number of individuals with insufficient intake. Prevalence estimates of inadequate and excessive intake are better for informing public health applications but require multiple urine samples per person; such estimates have been generated in pediatric populations but not yet among pregnant women.
Our aims were as follows: (1) to assess median urinary iodine concentrations across pregnancy for comparison with national data and (2) to estimate the prevalence of inadequate and excessive iodine intake among pregnant women in mid-Michigan.
Data were collected from 2008 to 2015 as part of a prospective pregnancy cohort in which women were enrolled at their first prenatal clinic visit. Few exclusion criteria (<18 years or non-English speaking) resulted in a sample of women generally representative of the local community, unselected for any specific health conditions. Urine specimens were obtained as close as practicable to at least 1 specimen per trimester during routine prenatal care throughout pregnancy (n=1-6 specimens per woman) and stored at -80°C until urinary iodine was measured to estimate the iodine intake (n=1014 specimens from 464 women). We assessed urinary iodine across pregnancy by each gestational week of pregnancy and by trimester. We used multiple urine specimens per woman, accounted for within-person variability, performed data transformation to approximate normality, and estimated the prevalence of inadequate and excessive iodine intake using a method commonly employed for assessment of nutrient status.
Maternal characteristics reflected the local population in racial and ethnic diversity and socioeconomic status as follows: 53% non-Hispanic white, 22% non-Hispanic black, and 16% Hispanic; 48% had less than or equal to high school education and 71% had an annual income of <$25,000. Median urinary iodine concentrations in the first, second, and third trimester-including some women contributing more than 1 specimen per trimester-were 171 μg/L (n=305 specimens), 181 μg/L (n=366 specimens), and 179 μg/L (n=343 specimens), respectively, with no significant difference by trimester (P=.50, Kruskal-Wallis test for equality of medians). The estimated prevalence of inadequate and excessive iodine intake was 23% and <1%, respectively.
Median urinary iodine concentrations in each trimester were above the World Health Organization cutoff of 150 μg/L, indicating iodine sufficiency at the group level across pregnancy. However, the estimated prevalence of inadequate iodine intake was substantial at 23%, whereas prevalence of excessive intake was <1%, indicating a need for at least some women to increase consumption of iodine during pregnancy. The American Thyroid Association, the Endocrine Society, and the American Academy of Pediatrics recommend that all pregnant and lactating women receive a daily multivitamin or mineral supplement that contains 150 μg of iodine. The data presented here should encourage the collection of similar data from additional US population samples for the purpose of informing the American College of Obstetricians and Gynecologists' own potential recommendations for prenatal iodine supplementation.
自 20 世纪 70 年代以来，美国的碘摄入量（根据代表性人群尿液碘中位数估计）下降了一半，这是一个问题，因为母体碘摄入量对胎儿神经发育至关重要。依靠尿液碘中位数来评估人群的碘摄入量是标准做法，但无法描述摄入不足的个体数量。摄入不足和过量的流行率估计值更有利于为公共卫生应用提供信息，但需要每人多次尿液样本；这些估计值已经在儿科人群中产生，但尚未在孕妇中产生。
我们的目的如下：（1）评估整个孕期的尿液碘中位数，与全国数据进行比较；（2）估计密歇根州中部孕妇碘摄入不足和过量的流行率。
数据收集于 2008 年至 2015 年期间，作为前瞻性妊娠队列研究的一部分，在第一次产前检查时招募了女性。只有不到 18 岁或不会说英语的少数排除标准导致了一个通常代表当地社区的一般女性样本，未针对任何特定健康状况进行选择。尽可能接近每位孕妇至少获得 1 份每个孕期的尿液样本（n=1-6 份/位女性），并在 -80°C 下储存，直到测量尿液碘以估计碘摄入量（n=1014 份样本来自 464 位女性）。我们通过每个孕期的妊娠周和妊娠分期来评估孕期的尿液碘。我们使用每位女性的多个尿液样本，考虑个体内的变异性，对数据进行转换以近似正态分布，并使用常用于评估营养状况的方法来估计碘摄入不足和过量的流行率。
母体特征反映了当地人口的种族和民族多样性以及社会经济地位，具体如下：53%的非西班牙裔白人、22%的非西班牙裔黑人、16%的西班牙裔；48%的人受教育程度低于或等于高中，71%的人年收入低于 25000 美元。第一、二和三期的中位数尿液碘浓度（包括一些每位孕妇贡献多于 1 份样本的情况）分别为 171μg/L（n=305 份样本）、181μg/L（n=366 份样本）和 179μg/L（n=343 份样本），各妊娠分期之间无显著差异（P=.50，Kruskal-Wallis 检验用于检验中位数的均等性）。碘摄入不足和过量的估计流行率分别为 23%和<1%。
每个孕期的中位数尿液碘浓度均高于世界卫生组织规定的 150μg/L，表明整个孕期的碘摄入在人群水平上是充足的。然而，估计碘摄入不足的流行率高达 23%，而过量摄入的流行率<1%，表明至少有一些孕妇需要在怀孕期间增加碘的摄入量。美国甲状腺协会、内分泌学会和美国儿科学会建议所有孕妇和哺乳期妇女服用含有 150μg 碘的每日多种维生素或矿物质补充剂。这里提出的数据应鼓励从其他美国人群样本中收集类似数据，以便为美国妇产科医师学会自身的产前碘补充建议提供信息。
