Sadly, about one in 33 infants born in the U.S. annually has one or more birth defects.
According to the CDC, “when discussing exposures and risk factors in regards to birth defects, we are talking about anything the fetus is exposed to as well as anything that may alter conditions within the womb. This includes everything the mother may come into contact with during pregnancy.”
The CDC goes on to highlight that most structural birth defects are associated with development of the fetus that occur early in pregnancy, during the “periconceptional” period (the month before and first 3 months after conception).
Thus, a significant share of birth defects research focuses on possible causes in the first trimester of pregnancy (the first 12 weeks).
Types of Birth Defects
The most common categories of birth defects are:
- Congenital heart disease – An abnormality in the heart that develops before birth.
- Down syndrome – A genetic chromosome 21 disorder causing developmental and intellectual delays.
- Cleft lip and cleft palate – Openings or splits in the roof of the mouth and lip.
- Spina bifida – A birth defect in which a developing baby’s spinal cord fails to develop properly.
- Club foot – A birth defect in which the foot is twisted out of shape or position.
- Phenylketonuria – A birth defect that causes an amino acid called phenylalanine to build up in the body.
- Edwards’ syndrome – A condition that causes severe developmental delays due to an extra chromosome 18.
The Eunice Kennedy Shriver National Institute of Child Health and Development provides further details on common birth defects in two major categories: Structural Birth Defects, and Functional or Developmental Birth Defects.
Our Research on Birth Defects
Studies cannot always provide a definitive answer about whether a particular exposure, risk factor or both caused a birth defect.
Instead, results are reported as changes in birth defects risk for exposed pregnancies compared to unexposed.
The Heartland Study is designed to explore possible linkages between prenatal herbicide exposure levels and birth outcomes, including the frequency of birth defects.
Known birth defects are relatively rare, collectively impacting just 3% of newborns. The frequency of specific birth defects is much lower. This is why epidemiological studies exploring the impacts of chemicals or other environmental causes on birth defects need to track birth outcomes in a large number of pregnancies. This is one reason for the Heartland Study’s ambitious goal of bringing at least 2,000 mother-infant pairs through our research protocol.
The Heartland Study will calculate risk ratios that reflect the odds of a given birth defect or adverse birth outcome occurring in the group of pregnant women most heavily exposed to herbicides, compared to the group that is exposed to the lowest average levels.
The CDC provides these benchmarks for evaluating the outcomes of epidemiological studies like the Heartland Study:
- Higher risks – a doubling or more – suggests an association between the exposure and the condition in question. This may mean the studied exposure/risk factor contributes to the birth defect.
- Decreased risks – one half or less – indicates a protective effect. The exposure appears to prevent the birth defect from occurring.
- No change in risk – implies that the exposure and the defect are not closely related.
Several studies have reported associations between herbicide use and exposures and birth defects. We highlight a few below, or you can see all relevant bibliography records here.
- Exposure to the herbicide atrazine has been linked to increased incidence of hypospadias, a rare birth defect in male babies where the opening to the urethra is on the underside of the penis instead of the tip (Wintson et al., 2016), and chanal atresia or stenosis, a condition where the back of the nasal passage is blocked (Agopian et al., 2013A, Agopian et al., 2013B).
- Heartland Study Co-PI Paul Winchester documented that pesticide use was correlated with increased birth defects in the U.S. in this 2009 paper.
- Research on the Ontario Farm Family Study in Canada that was published in 2008 found that parental exposure to dicamba herbicide was significantly correlated to increased risk of birth defects in male babies.
- A key paper by Garry et al. published in 2002 found that farm families in Minnesota’s Red River Valley that conceived babies during the spring planting (and spraying) season were significantly more likely to be born with birth defects.