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Reproductive and Birth Outcomes

The fetus is developing along with critical organ systems during pregnancy. There are critical windows during the development when environmental exposures could damage the fetus growth and function. Additionally, fertility in men and women may be affected by environmental factors (NIEHS, 2020). We know some risk factors and others need more research to understand how family history, genetics, lifestyle, and environment interact to affect a couple's ability bring a healthy baby into the world.

Reproductive and Birth Outcome Measures

In New Mexico, we collect a constellation of measures relating to the ability to conceive, carry, and deliver a healthy, full-term baby that remains healthy throughout the first year of life. The measures are:

A healthy beginning
  • Preterm birth: a single (not multiple) baby born before 37 completed weeks of pregnancy and very preterm birth: a single baby born before 32 completed weeks of pregnancy. The measure is limited to singleton births because preterm birth rates differ dramatically between singleton and multiple births.
  • Low birth-weight: a baby born at, or over 37 weeks whose weight at birth is less than 5.5 lbs. (2500 grams) and very low birth weight: a baby born at any time in gestation, weighing less than 3.3 lbs. (1,500 grams). A low-birth-weight baby can be born too small, too early, or both. These conditions may have separate causes.
  • Infant mortality: death before the age of one year for every 1,000 live births within the same year. We also collect and report data on perinatal deaths, which include fetal deaths at, or over 28 weeks gestation, plus deaths in newborns less than 7 days old. Causes of fetal death are similar to causes of infant death in the first month of life so the combined data gives us a more complete picture.
  • Sex ratio at birth: the ratio of total males/total females born in a geographic area at a certain time.
  • Total fertility rate: the number of children that would be born to the average woman if she were to live to the end of her child-bearing years and give birth to children at the current age-specific fertility rates.

Risks and importance of the measures

Preterm birth: risk factors include delivering a premature baby in the past, being pregnant with multiples, tobacco use and substance abuse, and short time (less than 18 months) between pregnancies. Additionally, pregnancy complications can result in preterm birth because the baby must be delivered early. However, a woman can still have a premature birth even if she has no known risk factors.

Prematurity is the leading cause of death among newborn babies. Being born prematurely is also a risk for serious health problems; however, those babies born earliest are at greatest risk for medical complication or death. Those who survive may face lifelong problems such as intellectual disabilities, cerebral palsy, breathing and other respiratory problems, vision and hearing loss, and feeding and digestive problems.

Low birth weight: Risks include maternal smoking, alcohol consumption, inadequate weight gain/diet of the mother during pregnancy, exposure to air pollution (both indoor and outdoor), exposure to drinking water contaminated with chemical disinfection by-products or lead. Other factors, such as how genes, hormonal changes, maternal stress, racism, occupational and environmental factors, and infections contribute to prematurity and birthweight are being conducted.

Compared to babies of normal weight, low-birth-weight babies may be at increased risk for illness from 28 weeks of gestation through the first six days of the baby's life, infections, and the longer-term consequences of impaired development, such as delayed physical and social development or learning disabilities.

Infant mortality: Risk factors for death before the age of one year include: congenital abnormalities, prematurity, low birth weight, and air pollution in the form of particulate matter. Risk factors that may increase a woman's chance of fetal loss include: pre-pregnancy obesity, lower socio-economic status, older age, and exposure to chemicals during pregnancy.

Overall, congenital malformations, deformations, and chromosomal abnormalities are the leading cause of infant death (20.6% of deaths) (Almli LM, 2020) in the U.S., disorders related to short gestation and low birth weight are the second leading cause of infant death. However, it is important to keep in mind that cause of death varies over the first year of life and combining all causes during the first year of life obscures the importance of sudden infant death syndrome as the leading cause of death in the first few days after birth.

Sex ratio: Numerous studies have reported changes in the ratio (number of males divided by the number of females) at birth; many of the studies have found a fewer males born relative to females in different countries throughout the world. Although mechanisms for what determines the sex of the infant is not completely understood, some studies have suggested that environmental hazards, particularly endocrine disruptors, can affect how many males are born. Other factors besides environmental exposures can affect the sex ratio. A reduced sex ratio at birth has been linked to older-aged parents and parental smoking and an increased sex ratio has been linked to premature births.

Total fertility rate: Several indicators have been used to track fertility on a global, national, state and local level. Indicators most commonly used are the general fertility rate (GFR) which is defined as the number of live births divided by the total number of women of "reproductive age" (15-44 years), and the total fertility rate (TFR). The total fertility rate differs from the general fertility rate in that it adjusts for age-specific differences in fertility and shows the potential impact of current fertility patterns on reproduction allowing for more valid comparisons of rates across time and space.

Tips for healthy birth outcomes

The causes of low birth weight, preterm birth and infant mortality are often related. Therefore, to prevent these conditions it is important for all women of reproductive age to adopt healthy behaviors such as:

  • Quit smoking and avoid second-hand smoke,
  • Avoid drinking alcohol or taking drugs.
  • See your health care provider for a medical check-up before pregnancy. Work with your health care provider to control diseases such as high blood pressure or diabetes.
  • Talk with your health care provider about taking any medications.
  • Get prenatal care early, as soon as you think you may be pregnant, and throughout the pregnancy.
  • Discuss concerns during pregnancy with your health care provider, and provider and seek medical attention for any warning signs or symptoms of preterm labor.
  • Take a daily multivitamin containing 400 micrograms of folic acid, starting before and throughout pregnancy.
  • Learn about the quality of the water you drink (link).
  • Limit outdoor activity when air quality is poor. (link)
  • Reduce sources of indoor air pollutants, such as wood burning stoves and fireplaces. (link)
  • During pregnancy, stay away from mercury. Watch your consumption of fish, especially albacore tuna which may be contaminated with mercury. (link)
  • Stay away from lead and activities that can expose you to lead, such as going to firing ranges, stained glass hobbies, and furniture refinishing (link).
  • Maintain a healthy diet and weight and eat healthy, fresh foods.
  • If you are pregnant, don't apply pesticides and stay out of areas where pesticides have recently been applied. Prevent injuries and consider the safety of your home and family (e.g., wear seat belt, and install and test smoke alarms).
Tips for healthy outcomes