Glyphosate exposure in pregnancy and shortened gestational length: a prospective Indiana birth cohort study

Abstract

Background: Glyphosate (GLY) is the most heavily used herbicide worldwide but the extent of exposure in human pregnancy remains unknown. Its residues are found in the environment, major crops, and food items that humans, including pregnant women, consume daily. Since GLY exposure in pregnancy may also increase fetal exposure risk, we designed a birth-cohort study to determine exposure frequency, potential exposure pathways, and associations with fetal growth indicators and pregnancy length.

Method: Urine and residential drinking water samples were obtained from 71 women with singleton pregnancies living in Central Indiana while they received routine prenatal care. GLY measurements were performed using liquid chromatography-tandem mass spectrometry. Demographic and survey information relating to food and water consumption, stress, and residence were obtained by questionnaire. Maternal risk factors and neonatal outcomes were abstracted from medical records. Correlation analyses were used to assess relationships of urine GLY levels with fetal growth indicators and gestational length.

Results: The mean age of participants was 29 years, and the majority were Caucasian. Ninety three percent of the pregnant women had GLY levels above the limit of detection (0.1 ng/mL). Mean urinary GLY was 3.40 ng/mL (range 0.5-7.20 ng/mL). Higher GLY levels were found in women who lived in rural areas (p = 0.02), and in those who consumed > 24 oz. of caffeinated beverages per day (p = 0.004). None of the drinking water samples had detectable GLY levels. We observed no correlations with fetal growth indicators such as birth weight percentile and head circumference. However, higher GLY urine levels were significantly correlated with shortened gestational lengths (r = - 0.28, p = 0.02).

Conclusions: This is the first study of GLY exposure in US pregnant women using urine specimens as a direct measure of exposure. We found that > 90% of pregnant women had detectable GLY levels and that these levels correlated significantly with shortened pregnancy lengths. Although our study cohort was small and regional and had limited racial/ethnic diversity, it provides direct evidence of maternal GLY exposure and a significant correlation with shortened pregnancy. Further investigations in a more geographically and racially diverse cohort would be necessary before these findings could be generalized.

Keywords: Birth outcomes; Birth weight percentile; Caffeine; Exposure assessment; Gestational length; Glyphosate; Head circumference; Herbicides; Pregnancy; Roundup.

Fig. 1

Trends in urine GLY levels with key maternal characteristics and behavior: (a) Caffeine Intake, (b) Area of Residence, (c) Pre-pregnancy Body Mass Index (BMI), (d) Organic Food Consumption, and (e) Stress During Pregnancy. Legend: For group comparison, the p values were calculated using Fisher’s exact tests at significance level of 0.05. (a) The number of subjects with caffeine intake: < 8 oz. = 16, 8-24 oz. = 38, and > 24 oz. = 8; (b) number of subjects that lived in the residential area: rural = 14, suburban = 50, and urban = 7; (c) number of subjects with pre-pregnancy BMI: < 25 = 33, 25–30 = 20, and > 30 = 18; (d) number of subjects with frequency of organic food consumption: never = 10, rarely = 29, and frequently = 32; and (e) number of subjects with the degree of stress during pregnancy: not = 27, somewhat = 37, and very stressed = 6

Fig. 2

Monotonic relationships between urine GLY in pregnant women and their birth outcomes: (a) Birthweight Percentile, (b) Head Circumference, and (c) Gestational Length. Legend: A monotonic relationship shows that variables are changing concurrently, but not at the same rate, thus, this relationship is not linear. Spearman’s rank-based correlations (r) show here the strength and direction of the monotonic relationships between the urine GLY measures and birth outcomes. p-values were calculated at significance level of 0.05 with key confounders. Correlation analysis was adjusted for the confounders maternal age, BMI, tobacco use, alcohol use, and trimester of pregnancy