About a decade ago, a hypothesis was put forward to explain the preponderance of females among neural tube defect (NTD) fetuses. That hypothesis predicts that a woman's higher levels of early gestational intake of methyl groups, such as folic acid, will be associated with lesser male‐to‐female ratio differences in NTD‐affected births, specifically less preponderance of females. We explored this hypothesis in four distinct studies that investigated human NTDs, obtained information on folic acid, and capitalized on timing of folic acid fortification by investigating data that were collected both prior to and after the 1998 initiation of U.S. mandatory folic acid fortification of grains.

中文翻译：

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NTDs 和女性围孕期叶酸摄入量之间的男女比例。

大约十年前，提出了一个假设来解释神经管缺陷 (NTD) 胎儿中女性的优势。该假设预测，女性在妊娠早期摄入的甲基组（如叶酸）水平较高，将与受 NTD 影响的生育中男性与女性的比例差异较小有关，尤其是女性占优势的比例较低。我们在四项不同的研究中探讨了这一假设，这些研究调查了人类 NTD，获得了有关叶酸的信息，并通过调查 1998 年美国强制谷物叶酸强化之前和之后收集的数据来利用叶酸强化的时间。