Low Birthweight and Pre-Term Delivery

Low Birthweight

Any baby born before 39 weeks is preterm.

The CDC offers these definitions of term-related, birth rates and outcomes:

  • Full term delivery- Birth of a baby after 39 weeks of pregnancy.
  • Preterm birth rate- The number of births delivered at less than 37 completed weeks of gestation per 100 total births, based on the obstetric estimate of gestation.
  • Early preterm birth rate- The number of births delivered at less than 34 completed weeks of gestation per 100 total births, based on the obstetric estimate of gestation.
  • Late preterm birth rate- The number of births delivered at 34–36 completed weeks of gestation per 100 total births, based on the obstetric estimate of gestation.
  • Birth rate at 34, 35, and 36 weeks- The number of births delivered at the specified completed weeks of gestation per 100 total births, based on the obstetric estimate of gestation.
  • Singleton births- Births in single-gestation pregnancies.
  • Multiple births- Births in multiple-gestation pregnancies (i.e., twin and triplet and higher-order births).

In a web resource called “Why Is 40 Weeks So Important,” the New York Department of Health highlights that a full term delivery:

  • Reduces the risk of several health problems stemming from difficulty breathing, keeping warm, and nursing normally;
  • Lowers the incidence of newborn jaundice; and
  • Provides time for the baby’s brain and neurological system to fully develop (this part of the brain is responsible for more complex thinking  and it doubles in size during the last few weeks of pregnancy), lessening the risk of ADHD, autism, and metabolic or reproductive disorders as adults.

Key science is highlighted below, or see all relevant bibliography items on gestational length here.

Preterm Delivery

Babies born below 2,500 grams, or around 5.5 pounds, are considered low birthweight.

The CDC’s National Center for Health Statistics provides an overview of Birthweight and Gestation for the U.S. In 2017, CDC reports that:

  • 318,873 babies, or 8.3% of all live births, were born with low birthweights (less than 2500 grams, or 5.5 pounds);
  • 4% were born with very low birth weights;
  • 382,726 babies were born pre-term, or just under 10% of all live births.

Key science is highlighted below, or see all relevant bibliography items on birthweight here.

Key Science

  • In 2018, a Heartland Study research team published a paper found a “significant negative correlation” between urinary glyphosate levels and shorter gestational lengths.  In other words, women with higher amounts of the herbicide in their urine were more likely to have shorter pregnancies, if not necessarily preterm delivery.

Several other studies have reported an association between low-birth weight and/or pre-term delivery and pesticide exposures, including:

  • Earlier in his career, Heartland Study Co-PI Dr. Paul Winchester researched the incidence of preterm birth and shortened gestation in areas with high pesticide use in California.  In a paper published in 2016, he and his team identified an association between higher pesticide exposure and shorter gestation and lower birth weights.
  • Research on transgenerational, epigenetic impacts of herbicide exposure reported in 2018 that pregnant rats exposed to glyphosate were more likely to have offspring that in turn had shorter pregnancies, and gave birth to lower birthweight pups.

Birth Defects

Developmental Effects

Epigenetic Impacts

Reproductive Impacts: Conception & Pregnancy

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