The aim of this study was to summarise the available information regarding the partition of toxic metal (Cd, Hg, Mn, Pb) levels in the maternal/foetal unit from large epidemiological studies. We performed a systematic search of PubMed/MedLine, EMBASE, and ISI Web of Science for papers on Cd, total Hg, Mn or Pb levels in the maternal/cord blood that were published in English (n > = 200; 2010-2017). Data on year of publication, sample size, location, year of survey, and main results were extracted. We found a total of 35 papers. Most studies included large convenience samples of healthy pregnant women. The maternal/cord blood was properly used as a biomarker of prenatal exposure to toxic metals. The partition of these toxic metal levels in the maternal/foetal unit was metal-specific. Cd median levels (IQR) in cord blood reported worldwide were much lower [∼ 70% < LOD = ± 0.11 µg/L] than those found in maternal blood [0.23 µg/L (0.15 - 0.35), ∼ 65% > LOD]. Considering that Cd was under LOD in 70% of the cord blood, Cd cord:maternal ratio as well as Cd cord proportion were not provided. Total Hg median levels (IQR) in cord blood [0.75 µg/L (0.40 - 1.19), ∼30% < LOD = ±0.35 µg/L] were usually higher than in maternal blood [0.55 µg/L (0.40 - 0.85), ∼ 10% < LOD = ±0.15 µg/L]. Hg cord:maternal ratio was 1.34 (1.00 - 1.91), and infants born would have Hg cord:(cord + maternal) proportion ranged from 0.50 to 0.63. Mn was the only metal that was detected in 100% in both maternal (LOD : ±0.50 µg/L) and cord (LOD = ±0.2 µg/L) blood. Mn median levels (IQR) in cord blood [32.96 µg/L (26.90 - 40.10)] were 2 times higher than in maternal blood [14.01 µg/L (11.50 - 17.58)]. Mn cord:maternal ratio was 2.35 (1.09 - 3.80), and infants born would have Mn proportion ranged from 0.52 to 0.79. Pb median levels (IQR) in cord blood [5.79 µg/L (4.34 - 8.38), ∼ 5% < LOD : ±2.07 µg/L] were usually equal to or lower than those reported in maternal blood [8.07 µg/L (5.79 - 10.76), ∼ 1% < LOD = ±1.03 µg/L]. Pb cord:maternal ratio was 0.71 (0.59 - 0.96), and infants born would have Pb proportion ranged from 0.37 to 0.49. Globally, the results indicate that total Hg and Mn levels were lower in maternal blood but higher in cord blood. However, much greater variability was seen with Cd and Pb. At delivery, total Hg and Pb levels in maternal blood were strong predictors of cord blood levels. Our findings empty that understanding the partition, levels and correlations of toxic metals in the maternal/cord blood may help to elucidate the adverse effects of these metals on foetuses and neonates.

中文翻译：

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母体/胎儿单位中的有毒金属（Cd、Hg、Mn、Pb）分配：近期流行病学研究的系统小型回顾

本研究的目的是总结来自大型流行病学研究的有关母体/胎儿单位中有毒金属（Cd、Hg、Mn、Pb）水平分配的可用信息。我们对 PubMed/MedLine、EMBASE 和 ISI Web of Science 进行了系统搜索，以查找有关母体/脐带血中 Cd、总 Hg、Mn 或 Pb 水平的英文论文（n > = 200；2010-2017） . 提取出版年份、样本量、地点、调查年份和主要结果的数据。我们一共找到了 35 篇论文。大多数研究包括健康孕妇的大量方便样本。母体/脐带血被适当地用作产前接触有毒金属的生物标志物。这些有毒金属水平在母体/胎儿单元中的分配是金属特异性的。全球报道的脐带血中 Cd 中值水平 (IQR) 远低于母血 [~ 70% < LOD = ± 0.11 µg/L] [0.23 µg/L (0.15 - 0.35)，~ 65% > LOD] . 考虑到 70% 的脐带血中 Cd 低于 LOD，因此未提供 Cd 脐带：母体比例以及 Cd 脐带比例。脐带血中的总汞中值水平 (IQR) [0.75 µg/L (0.40 - 1.19), ∼30% < LOD = ±0.35 µg/L] 通常高于母血 [0.55 µg/L (0.40 - 0.85) , ∼ 10% < LOD = ±0.15 µg/L]。Hg 脐带：母体比为 1.34（1.00 - 1.91），出生婴儿的 Hg 脐带：（脐带 + 母体）比例为 0.50 至 0.63。Mn 是唯一在母体 (LOD：±0.50 µg/L) 和脐带 (LOD = ±0.2 µg/L) 血液中 100% 检测到的金属。脐带血中锰的中值水平 (IQR) [32.96 µg/L (26.90 - 40. 10)] 比母血 [14.01 µg/L (11.50 - 17.58)] 高 2 倍。Mn 脐带：母体比为 2.35 (1.09 - 3.80)，出生的婴儿的 Mn 比例在 0.52 至 0.79 之间。脐带血中铅的中值水平 (IQR) [5.79 µg/L (4.34 - 8.38), ∼ 5% < LOD : ±2.07 µg/L] 通常等于或低于母血 [8.07 µg/L ( 5.79 - 10.76)，∼ 1% < LOD = ±1.03 µg/L]。Pb 脐带：母体比率为 0.71 (0.59 - 0.96)，出生的婴儿的 Pb 比率范围为 0.37 至 0.49。在全球范围内，结果表明母血中的总 Hg 和 Mn 水平较低，但脐带血中的总水平较高。然而，Cd 和 Pb 的变异性要大得多。分娩时，母血中的总 Hg 和 Pb 水平是脐带血水平的强预测因子。我们的发现消除了对分区的理解，