Increases in risk of prematurity or preterm delivery have been related to exposures to air pollution, lead, and some solvents during pregnancy. 

Exposure and Risk 
There are some known risk factors for premature birth. Even if a woman does everything "right" during pregnancy, unfortunately a premature infant may still be born. 

The known risk factors for pre-term birth are:

• Carrying multiple fetuses (twins, triplets, quadruplets or more)
• Having a previous preterm birth
• Problems with the uterus or cervix
• Chronic maternal health problems such as high blood pressure, diabetes, and clotting disorders
• Certain infections during pregnancy
• Cigarette smoking, alcohol use, or illicit drug use during pregnancy
• Exposure to secondhand smoke

 

Other potential risk factors are:

• Mother's age, race, poverty
• African-American women, women younger than 17 years and older than 35 years, and poor women are at greater risk than other women
• Male babies, associated with singleton preterm birth
• Certain lifestyles and environmental factors, including:
  • Late or no prenatal care
  • Social and economic factors
  • domestic violence
  • lack of social support
  • stress
  • marital status
• long working hours with long periods of standing
• being underweight or overweight before pregnancy
• spacing of births, less than 6-9 months between birth and the beginning of the next pregnancy
• Environmental chemicals: For example, exposure to air pollution or drinking water contaminated with lead

Prevention 
Preterm births can occur for no obvious reason; many women who have a premature birth have no known risk factors. Women who are pregnant or may become pregnant should be urged to comply with the following advice to both improve their own health and lower their risk of having a premature baby:

• Quit smoking and avoid secondhand smoke
• Do not use alcohol or illegal drugs
• See a health care provider for a medical checkup before becoming pregnant
• Work with a health care provider to control diseases such as high blood pressure or diabetes
• Get prenatal care as early as possible and continue care throughout the pregnancy
• Discuss concerns during pregnancy with a health care provider, and seek medical attention for any warning signs or symptoms of preterm labor

Warning signs may include: Contractions every 10 minutes or more often

• Contractions every 10 minutes or more often
• Change in vaginal discharge
• Pelvic pressure
• Cramps
• Abdominal cramps with or without diarrhea

 

Low Birthweight 

LowBirthweight and the Environment
Birth weight is the first weight of the newborn measured immediately after birth. Birth weight of less than 5.5 lbs, or 2500 grams, is considered low birth weight.

A low birth weight infant can be born too small, too early, or both. These conditions often have separate causes. Specific factors may be related to one of these conditions but not the other. For example, smoking during pregnancy is more related to infants born too small (growth retardation) than too early (prematurity). For this reason, low birth weight in the Tracking Network includes only infants who are born full-term.

Compared to infants of normal weight, low birth weight infants may have an increased risk for many negative circumstances. Some of these circumstances are illness through the first six days of life (perinatal morbidity), infections, and the longer-term consequences of impaired development, such as delayed motor and social development or learning disabilities.

Reductions in birth weight or increases in low birth weight have been associated with exposure to lead, solvents, pesticides, polycyclic aromatic hydrocarbons (PAHs), and air pollution during pregnancy. 

Exposure and Risk 
Low birth weight is associated with many risk factors, including:

• Maternal smoking
• Maternal alcohol consumption
• Inadequate maternal weight gain
• Mothers younger than 15 years and older than 35 years
• Social and economic factors
• low income
• low educational level
• stress
• domestic violence or other abuse
• unmarried
• Mothers who have had a previous preterm birth
• Exposure to air pollution (both indoor and outdoor) and drinking water contaminated with lead, which are considered environmental risk factors

Intrauterine growth retardation is associated with the following risk factors:

• Maternal smoking
• Maternal alcohol consumption
• Inadequate maternal weight gain

Prevention 
Early and continuous prenatal care helps identify conditions and behavior that can result in low birth weight infants, such as smoking, drug and alcohol abuse, inadequate weight gain during pregnancy, and pregnancy again in six months or less. Infants born to teenage mothers have a higher risk of being low birth weight babies and a higher mortality rate.

To reduce the risk of having a low-birth weight infant, a woman can:

• Quit smoking
• See your health care provider for a medical checkup before pregnancy
• Work with your health care provider to control diseases such as high blood pressure or diabetes
• Get prenatal care as early as possible and throughout the pregnancy
• Discuss concerns during pregnancy with a health care provider, and seek medical attention for any warning signs or symptoms of preterm labor
• Take a daily multivitamin containing 400 micrograms of folic acid before and throughout pregnancy

 

Infant and Perinatal Mortality 
Infant and Perinatal Mortality and the Environment
Infant mortality is defined as when an infant dies less than 1 year of age. Perinatal mortality is defined as death after the 28th week of pregnancy, but before the 7th day of age.

The fetus and infant may be particularly susceptible to harmful effects of environmental contaminants. Many environmental contaminants may be especially toxic in the womb. Many cross the placenta and make their way into the circulatory system of the developing fetus. Even if a potentially harmful exposure is identified, the health effects on the fetus are often not well understood until years later.

Environmental exposure-related causes of infant and perinatal death are only one factor. Other factors include access to and quality of health care, competency in childcare and understanding injury prevention.

Outdoor air pollution is one example of a connection between environmental health and infant death. Air pollution in the form of particulate matter (PM10) has been associated with an increase in the rate of postneonatal deaths. Postneonatal deaths occur from age 28 days through the first year of life. The major causes of death associated with PM10 exposure were deaths from respiratory causes and Sudden Infant Death Syndrome, or SIDS.

Pesticides have been associated with fetal death and spontaneous fetal losses but more research is needed to determine the degree of association. 

Exposure and Risk

 
The leading causes of infant death include:

• congenital abnormalities
• pre-term/low birth weight
• SIDS
• problems related to complications of pregnancy
• respiratory distress syndrome

 

Unexplained fetal death and death related to growth restriction are the leading causes of fetal loss. Fetal death is a significant source of mortality, with the rate being many times higher than the rate of SIDS among infants.

Markers of increased risk for fetal loss include:

• pre-pregnancy obesity
• lower socioeconomic status
• non-Hispanic black race
• advanced maternal age
• exposure to pesticides

Prevention 
Health care providers should advise their patients about factors that affect birth outcomes, such as maternal smoking, illegal drug and alcohol abuse, poor nutrition, stress, insufficient prenatal care, chronic illness, or other medical problems. Communities can play an important role in this effort by:

• encouraging pregnant women to seek prenatal care in the first trimester
• educating providers, pregnant women, and family members on factors that affect infant mortality such as:
  • smoking,
  • substance abuse,
  • poor nutrition,
  • lack of prenatal care,
  • medical problems, and
  • chronic illness.

Parents and caregivers should always place sleeping infants on their backs. Research has demonstrated that infants who sleep on their stomachs or sides are at higher risk for SIDS. A sleeping environment separate from the parents' bed, such as a crib in the parents' bedroom, is recommended. 

 

Fertility and Infertility 

Fertility and Infertility and the Environment
According to data from the National Survey of Family Growth, 12% of U.S. couples had impaired fertility in 2002, up 20% from 1995. Approximately 10% of problems with fertility are unknown and environmental contaminants including endocrine disruptors have been hypothesized as major contributors. Environmental contamination can have multi-generational impacts on reproduction that need to be studied and tracked long term. 

Exposure and Risk 
The following factors increase a woman's risk of infertility:

• age
• stress
• poor diet
• athletic training
• overweight or underweight
• tobacco use
• alcohol consumption
• sexually transmitted diseases (STDs)
• health problems that cause hormonal changes

The number produced and quality of a man's sperm can be affected by his overall health and lifestyle. The following factors may reduce sperm number and quality include:

• alcohol
• illegal drugs
• environmental toxins
• tobacco use
• medicines
• radiation treatment or chemotherapy for cancer
• age

Prevention 
Most healthy women younger than 30 years should not be concerned about infertility unless they have been attempting to conceive for at least a year. At this point, women and their partners should consult their doctors about a fertility evaluation. 

Women in their 30s who have been trying to conceive for six months should consult their doctors as soon as possible. A woman's probability of conceiving decreases rapidly every year after the age of 30; receiving a complete and timely fertility evaluation is especially important.

Some health issues also increase the risk of fertility problems. Women with the following issues should consult their doctors as soon as possible:

• irregular or no menstrual periods
• very painful periods
• endometriosis
• pelvic inflammatory disease
• more than one miscarriage

Regardless of age, women should consult a doctor before attempting to conceive. Doctors can help women prepare their body for a healthy baby. They can also answer questions on fertility and give advice on conceiving. 

Sex Ratio

Sex Ratio and the Environment
The sex ratio at birth is the ratio of male to female births. The expected sex ratio at birth (male to female) is 1.05. 

Population growth is, in part, related to the number of live male children. Numerous studies have reported changes in the ratio of males to females at birth. How the sex of an infant is determined is unclear. Some scientists have suggested that environmental hazards can affect how many males are born. Parents and the fetus can come in contact with, and become exposed to, different hazards referred to as endocrine disruptors. Fewer males are conceived when exposure to endocrine disruptors causes a decrease in testosterone.

Diethylstilbestrol (DES), a synthetic estrogen widely prescribed to pregnant women during the mid-1900s, is a potent endocrine disruptor. Previous studies have suggested an association between endocrine-disrupting compounds and secondary sex ratio. The secondary sex ratio is the sex ratio of the grandchildren of the exposed women. 

Exposure and Risk 
Factors other than endocrine disruptors can affect the expression of sex. Decreases in male births are inversely related to parental smoking, gestation length, parental age, and birth order. Reproductive practices and social morays regarding sex preferences of males over females, for example, can affect the observed sex ratio. 

Prevention 
Because states have accurate vital statistics records on the sex of live births, changes over time in the sex ratio of infants can be measured as the ratio of males to females. This ratio of total males/total females born in a geographic area such as state, county, zip code, census tract, or block group, at a certain time, and for one birth year or multiple years, is referred to as the sex ratio.​