Although the reasons for the development of most birth conditions are unknown, scientific research has identified both environmental and genetic factors that can be associated with birth conditions.
Finding the causes of birth defects has become a priority area for many in the field of maternal and child health. Research has proven conclusively that a variety of human factors, such as insufficient folic acid and advanced maternal/paternal age at conception, can cause birth defects, but studies investigating the role of environmental hazards have not been as consistent or strong in association for several reasons.
First, it is difficult to study the relationship between environmental factors and birth defects simply because the number of birth defects cases is too small. Some researchers have tried to increase the number of cases by grouping together similar birth defects, such as heart-related birth defects, but this is not always effective since researchers have found that different environmental hazards can cause one specific type of birth defect within a grouping of birth defects, while a specific environmental hazard can cause many different types of birth defects.
Timing of exposure to the environmental hazard during pregnancy is also a limiting factor in studying birth defects. A good example of this is the drug Thalidomide. Thalidomide causes severe limb deformities in children of mothers who took the drug during the third to sixth week of pregnancy, but not at any other time. Thalidomide was also associated with an increased risk of autism, but only if taken 20-24 days after conception.
These issues combined with genetics, nutrition, the health of the mother, and other factors that can affect the chances of a child being born with a birth defect, make studying the relationship between the environment and birth defects extremely difficult. While more studies and information are needed before conclusive statements regarding the causal effect of environmental hazards can be made, it is important to know what has been discovered so far.
Certain environmental hazards have the potential to cause birth defects and developmental disabilities. These include lead, mercury, polychlorinated biphenyl (PCB), arsenic, pesticides, carbon monoxide, ozone, and runoff from landfills and hazardous waste sites.
Pregnant women may be exposed to lead through inhalation during lead abatement, ingestion from water that has passed through lead pipes, from eating or drinking from lead crystal glasses or lead-containing ceramic dishes, or from certain arts and crafts material. Although few pregnant women in this country are exposed to high enough levels of lead to cause concern, babies born to women who are highly exposed are more likely to have developmental disabilities or birth defects, be stillborn, or be born preterm or of low birth weight.
Mercury is another environmental factor linked to developmental disabilities. Most pregnant women are exposed to mercury by eating contaminated fish. In 2004, the US Food and Drug Administration and the Environmental Protection Agency advised women who are pregnant, or might become pregnant, to follow these three recommendations
- Do not eat shark, swordfish, king mackeral, or tilefish
- Eat up to 12 ounces (2 meals) a week of a variety of fish and shellfish that are low in mercury (shrimp, canned light tuna, salmon, pollock, and catfish are the best). Albacore (white) tuna is higher in mercury than canned light tuna; if albacore tuna is consumed as a meal, then no other fish should be eaten during that week.
- Check local advisories about the safety of fish caught by friends and family. If a local advisory is unavailable and locally caught fish is consumed, then no other fish should be eaten during that week.
Another environmental contaminant found in fish is polychlorinated biphenyl or PCB. Exposure to PCB during pregnancy may contribute to developmental disabilities, birth defects, and low birth weight in babies. Before consuming locally caught fish, check with the state health department or fish and game department for PCB advisories in the area. The EPA should also be able to provide this information.
Arsenic in drinking water is a concern for all New Hampshire residents with private wells. Arsenic is present in the bedrock layer that many wells are drilled into and can cause birth defects and low birth weight in babies, as well as bladder cancer in adults. Because you cannot tell if arsenic is present in well water by sight or taste, it is important to have your well water tested and treated if the level is high. Well water testing is available through the NH Department of Environmental Services. If water is tested for arsenic, also have it tested for cadmium and nitrates because both can also affect the developing fetus. Arsenic can also be found in pressure-treated lumber and it is recommended that pregnant women avoid construction projects with pressure-treated lumber.
Pesticides used at normal levels in the home have not been found to pose a risk to pregnant women; however, it is best for pregnant women to reduce their level of exposure by having someone else apply the pesticides, open the windows to allow ventilation, and wipe off all counters where food is prepared. Pesticide use for farming should be avoided due to their potential to cause birth defects, miscarriage, and preterm delivery. The insect repellant DEET has not been sufficiently studied, so pregnant women should NOT apply DEET directly to their skin and should use gloves when spraying the repellant on their clothes or on others.
Air pollution in the form of carbon monoxide and ozone has been linked to heart defects. Women exposed to high levels of these two pollutants during the second month of pregnancy are more likely to have infants with various heart defects. Heart formation occurs primarily in the 2 nd month of pregnancy and the higher the level of ozone and carbon monoxide, the higher the risk for heart defects.
Many express concern over birth defects caused by contaminants from nearby toxic/hazardous waste sites, landfills, and other dumpsites. These are valid concerns as studies have found elevated risks for birth defects in areas near those sites. Birth defects associated with living near waste sites, landfills, and other dumpsites include heart defects, central nervous system disorders, musculoskeletal defects, oral clefts, and neural tube defects, as well as low birthweight and intrauterine growth retardation.
Some pregnant women are exposed to hazards at the workplace. Women who are employed as factory workers, laboratory technicians, artists, graphic designers, printing industry workers, hairstylists, semi-conductor plant workers, photography developers, silk screeners, or have hobbies that involve using solvents, are at risk for increased birth defects among exposed fetuses. Common organic solvents include alcohols, degreasers, paint thinners and varnish removers, lacquers, silk-screening inks, and some paints. Women who work with these types of chemicals should make sure the workplace is well ventilated, that appropriate clothing is worn, and that food and drinks are not consumed in the workplace. Birth defects associated with organic solvent exposure are frequently severe and include heart defects, oral clefts, neural tube defects, limb reduction defects, gastroschisis (intestine protrudes through a hole in abdomen), and other major structural birth defects.
Many of the risks associated with environmental hazards can be avoided by adopting a prevention strategy and using a little common sense. If you have concerns or questions, ask a health care provider.
Although the cause of many birth defects is still unknown, some birth defects are caused by genetic factors. A genetic counselor can help to understand whether birth defects in a person's family are genetic and if they have a chance of recurring. When a couple meets with a genetic counselor, a thorough family history is taken. You will discuss any risk actors to your pregnancy, review genetic and prenatal testing options, and explore any concerns or questions that you have.
People see genetic counselors for several reasons:
- Maternal age – Women who are 35 or older at the time of delivery
- Family history of birth defects, stillbirth, multiple miscarriages
- Known genetic disorders in the family or developmental delays
- Previous child or family member with a chromosomal disorder (such as Down syndrome)
- Abnormal prenatal screening results
- Couples going through in-vitro fertilization (IVF) or other infertility procedures (ICSI)
- Abnormal ultrasound
- Certain ethnic groups have a higher risk of genetic diseases
In addition to genetic counseling, there are several types of tests that are available to help determine the risk for having a baby with a birth condition. These tests include:
First Trimester Screening Thiscombines ultrasound and maternal blood testing to estimate the risk of Down syndrome and Trisomy 18. It is done between 11 and 13 weeks of pregnancy.
Maternal Serum Screening This is a blood screening test performed between 15-20 weeks gestation. Maternal Serum Screening is used to estimate the risk of Down syndrome, Trisomy 18, and open neural tube defects (such as spina bifida).
Ultrasound This can provide information about size, growth, and the presence of twins, in addition to identifying certain birth defects. High-resolution ultrasound evaluation at 18-20 weeks is used to screen for certain chromosome disorders, including Down syndrome.
Amniocentesis or Chorionic Villus Sampling (CVS) These involve the collection of a sample of cells from around the baby by inserting a thin needle into the womb or through the cervix. These are diagnostic tests that identify chromosome abnormalities and are performed at 15 -20 weeks (amniocentesis) or 10-12 weeks (CVS).
For more information on genetic conditions please see the following resources: