Reproductive Health and Birth Outcomes and the Environment
Adverse reproductive and birth outcomes may include infertility, low birth weight, prematurity, and fetal and infant death. Research on reproductive and birth outcomes has improved understanding of the risks of several substances found in the environment. Results from research into the role specific environmental hazards play in these outcomes have been inconsistent. Some authors have suggested increased rates of adverse birth outcomes; others have found no effect. The following risk factors reflect the limited knowledge of the environment’s role.
There are a variety of recognized teratogens that women may be exposed to during pregnancy and many substances that have not been recognized as teratogens yet. A teratogen is any agent or organism that results in death or abnormality when a fetus is exposed to it. The criteria applied to prove teratogenicity include proven exposure to the agent at critical times during the prenatal period; reports of similar outcomes in epidemiologic studies; documentation of clinical cases and presentation; teratogenicity in animal models; and experimental proof when available. A listing of known and suspected teratogens is found in the Catalog of Teratogenic Agents by Thomas Shepard.
Teratogens may include infections such as listeria, rubella, toxoplasmosis, parvovirus, cytomegalovirus, sexually transmitted infections and HIV. It is difficult to determine the extent to which infections result in fetal loss.
Environmental exposures to lead, radiation, chemicals, medication and anesthetic agents such as nitrous oxide, have been implicated in pregnancy loss. Current epidemiologic surveys do not indicate that there are proven hazards to operating room personnel from trace anesthetic gases.
Pesticide exposures have been linked to an increase in late fetal and neonatal death (between 20 weeks and term gestation) due to congenital anomalies. The risk appears highest when women live within a mile of the area where the pesticide is applied and are exposed during the third to eighth week of pregnancy. Pesticides that have been associated with fetal death include
Arsenic , found in higher levels in women living or working near metal smelting plants or who consume drinking water contaminated with arsenic based fertilizers, has been associated with increased pregnancy loss.
Medications associated with unexpected or adverse pregnancy outcomes include retinoid medications, methotrexate, non-steroidal anti-inflammatory medications, lithium, androgen hormones, captopril, cocaine, Coumadin, enalapril, mercury, tetracyclines, thalidomide and valproic acid.
Severe malnutrition as sometimes seen in anorexia and bulimia, as well as obesity can predispose to pregnancy loss. Some endocrine disorders, such as poorly controlled diabetes and thyroid disorders can also impact pregnancy outcome.
Although seldom considered, paternal factors can also impact reproductive outcomes. Exposure of the father to high levels of lead may result in a significant increase in miscarriage. Chronic alcohol abuse has an impact on the immune system and hormone secretion in the offspring in animal models. Advanced paternal age can result in cellular mutations resulting in conditions such as neurofibromatosis and achondroplasia (a form of dwarfism). Paternal age may also affect the incidence of Down syndrome.