根據美國印第安納大學醫學院，臨床小兒科教授的研究，美國早產兒發生比例的上升，和殺蟲劑與含硝酸鹽的肥料使用增加有關。
溫徹斯特醫師（Paul Winchester）7日發表他的調查結果表示：「有越來越多的證據顯示，產前暴露在殺蟲劑、硝酸鹽類、和其他環境污染物之下，對許多懷孕的結果有害。身為小兒科醫生，我看到新生兒缺陷、早產兒有增加的趨勢，我想我們需要更勇敢的面對環境所造成的後果。」
早產兒是指在懷孕滿37週前出生的嬰兒。在美國早產兒發生比例約佔8-10%。根據美國疾病預防控制中心，衛生統計部門的資料，自1981年政府開始追蹤早產兒至2005年為止，美國早產兒的比例增加約30%。
溫徹斯特及其同僚發現，早產兒的比例，與殺蟲劑和硝酸鹽水面測量值最高的4-7月間同時達到高峰，而8-9月硝酸鹽和殺蟲劑含量最低時，早產率也最低。
早產率最高發生在5月和6月，約11.91%，最低的10.79%在8月和9月。這些結果不受母親年齡、種族、教育程度、婚姻狀況、喝酒與吸菸、或是母親居住在城市、郊區、農村的影響。
根據美國地質調查所的研究，殺蟲劑和硝酸鹽類在水面的含量也在5-6月最高，而8-9月最低。
溫徹斯特說：「美國早產兒隨著不同的月分有週期性和季節性的變化。而水面殺蟲劑和硝酸鹽含量在美國各處也有相似的變化。硝酸鹽與殺蟲劑會中斷荷爾蒙的分泌，而一氧化氮則來到成長中胎兒的地方。」
The rising rate of premature births in the United States is associated with the increased use of pesticides and fertilizers containing nitrates, according to research by a professor of clinical pediatrics at the Indiana University School of Medicine.
"A growing body of evidence suggests that the consequence of prenatal exposure to pesticides and nitrates as well as to other environmental contaminants is detrimental to many outcomes of pregnancy. As a neonatologist, I am seeing a growing number of birth defects, and preterm births, and I think we need to face up to environmental causes," Paul Winchester, MD, reports his findings today.
A premature baby is born before the 37th week of pregnancy. Premature birth occurs in between eight to 10 percent of all pregnancies in the United States. The rate of premature birth in the United States has risen about 30 percent between 1981, when the government began tracking premature births, and 2005, according to the National Center for Health Statistics, a division of the Centers for Disease Control and Prevention.
Winchester and his colleagues found that preterm birth rates peaked when pesticides and nitrates measurements in surface water were highest, from April through July, and were lowest when nitrates and pesticides were lowest, in August and September.
The highest rate of prematurity, 11.91 percent, occurred in May and June and the lowest, 10.79 percent in August and September. These results were independent of maternal age, race, education, marital status, alcohol or cigarette use, or whether the mother was an urban, suburban or rural resident.
Pesticide and nitrate levels in surface water were also highest in May-June and lowest in August and September, according to the U.S. Geological Survey.
"Preterm births in the United States vary month to month in a recurrent and seasonal manner. Pesticides and nitrates similarly vary seasonally in surface water throughout the U.S. Nitrates and pesticides can disrupt endocrine hormones and nitric oxide pathways in the developing fetus," Winchester said.
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