while pregnant, thus increasing the likelihood that both mother and baby could be exposed. routes of exposure harmful substances can enter a woman's body through breathing in (inhalation), contact with the skin, or swallowing (ingestion). pregnant workers and those planning to become pregnant should be especially concerned about exposure to reproductive hazards. some chemicals (such as alcohol) can circulate in the mother's blood, pass through the placenta, and reach the developing fetus. other hazardous agents can affect the overall health of the woman and reduce the delivery of nutrients to the fetus. radiation can pass directly through the mother's body to harm her eggs or the fetus. some drugs and chemicals can also pass through a mother's body into the nursing baby through the breast milk. reproductive hazards do not affect every woman or every pregnancy. whether a woman or her baby is harmed depends on how much of the hazard they are exposed to, when they are exposed, how long they are exposed, how they are exposed, and personal factors like age, stage of menstrual cycle, stage of pregnancy or when exposure occurs. for example, exposure to a hazard could block ovulation and pregnancy only at specific times of the menstrual cycle. exposure during the first 3 months of pregnancy might cause a birth defect or a miscarriage. exposure during the last 6 months of pregnancy could slow the baby's growth, affect its brain development, or cause premature labor. workplace substances that affect female workers and their pregnancies can also harm their families. without knowing it, workers can bring home harmful substances that can affect the health of other family members—both adults and children. for example, lead brought home from the workplace on a worker's skin, hair, clothes, shoes, tool box, or car can cause lead poisoning in family members, especially young children. occupational reproductive hazards a number of occupational hazards can impact reproductive health and subsequently reproductive outcomes including chemical, physical, and psychosocial hazards. although more than 1,000 workplace chemicals have been shown to have reproductive effects on animals, most have not been studied in humans. in addition, most of the 4 million other chemical mixtures in commercial use remain untested. some reproductive hazards include: anesthetic gases antineoplastic (cancer treatment drugs) chemical disinfectants and sterilants certain ethylene glycol ethers such as 2-ethoxyethanol (2ee) and 2-methoxyethanol (2me) carbon disulfide (cs2) epoxies and resins ethylene oxide formaldehyde heat infectious agents lead and other heavy metals noise pesticides ionizing radiation non-ionizing radiation secondhand smoke smoke and by-products of burning solvents shift work and long working hours strenuous physical demands (e.g. prolonged standing, heavy lifting, bending) many chemicals are not evaluated for reproductive toxicity and occupational exposure limits are developed based on nonpregnant adults. exposure levels considered safe for an adult may, or may not be safe for a fetus. reproductive health problems that might be caused by workplace exposures workplace hazards can lead to certain reproductive health problems, such as: reduced fertility or infertility erectile dysfunction menstrual cycle and ovulatory disorders women's health problems linked to sex hormone imbalance miscarriage stillbirth babies born too soon or too small birth defects child developmental disorders childhood cancers occupational hazards and female reproductive health some workplace hazards can affect reproductive health, the ability to become pregnant, and the health of unborn children. most women can safely keep working in their job during their pregnancy. but some jobs involve exposures that are harmful to pregnant or breastfeeding women. some female health problems that may be caused by workplace reproductive hazards include the following: disruption of the menstrual cycle and hormone production high levels of physical or emotional stress or exposure to chemicals such as pesticides, polychlorinated biphenyls (pcbs), organic solvents and carbon disulfide, may disrupt the balance between the brain, pituitary gland, and ovaries. this disruption can result in an imbalance of estrogen and progesterone, and lead to changes in menstrual cycle length and regularity and ovulation. because these sex hormones have effects throughout a woman's body, severe or long-lasting hormone imbalances may affect a woman's overall health. hazards that can disrupt the menstrual cycle and/or sex hormone production include: a variety of pesticides carbon disulfide (cs2) polychlorinated biphenyls (pcbs) organic solvents jet fuel shift work infertility and subfertility about 10% to 15% of all couples are infertile or have subfertility, which means that they are unable to conceive a child after 1 year of trying to become pregnant. many factors can affect fertility, and these factors can affect one or both partners. damage to the woman's eggs or the man's sperm, or a change in the hormones needed to regulate the normal menstrual cycle are just a few things that can cause problems with fertility. more common causes of infertility include: damage to the woman's eggs damage to the man's sperm infertility can be caused by change in the hormones needed to regulate the normal menstrual cycle and uterine growth. hazards that can reduce fertility in women include: cancer treatment drugs, including antineoplastic drugs lead ionizing radiation, including x-rays and gamma rays nitrous oxide (n2o) miscarriages and stillbirths about 1 in every 6 pregnancies ends in a miscarriage—the unplanned termination of a pregnancy. miscarriages can occur very early in pregnancy, even before the woman knows she is pregnant. miscarriages and stillbirths occur for many reasons, such as the following: the egg or sperm may be damaged so that the egg cannot be fertilized or cannot survive after fertilization. a problem may exist in the hormone system needed to maintain the pregnancy. the fetus may not have developed normally. physical problems may exist with the uterus or cervix. birth defects a birth defect is a physical abnormality present at birth, though it may not be detected until later. about 2% to 3% of babies are born with a major birth defect. in most cases, the cause of the birth defect is unknown. the first 3 months of the pregnancy is a very sensitive time of development because the internal organs and limbs are formed during this period. many women are not aware that they are pregnant during much of this critical period. low birth weight and premature birth about 7% of babies born in the united states are born underweight or prematurely. poor maternal nutrition, smoking, and alcohol use during pregnancy are believed to be responsible for most of these cases. although better medical care has helped many underweight or premature babies to develop and grow normally, they are more likely than other babies to become ill or even die during their first year of life. developmental disorders sometimes the brain of the fetus does not develop normally, which leads to developmental delays or learning disabilities later in life. about 10% of children in the united states have some form of developmental disability. such problems are often not noticeable at birth. they can be difficult to measure, may be temporary or permanent, and range from mild to severe. developmental problems may appear as hyperactivity, short attention span, reduced learning ability, or (in severe cases) intellectual disability. other health problems even if a woman is not trying to become pregnant, her general health can be harmed by reproductive hazards that alter the production of sex hormones. sex hormones have effects throughout a woman's body. some workplace exposures can cause an imbalance of estrogen and progesterone levels in the blood. this disruption can increase vulnerability to: some cancers, such as endometrial or breast cancer osteoporosis heart disease tissue loss or weakening effects on the brain and spinal cord, including symptoms of menopause occupational hazards and male reproductive health a number of workplace substances have been identified as reproductive hazards for men such as: lead dibromochloropropane carbaryl (sevin ) toluenediamine and dinitrotoluene ethylene dibromide plastic production (styrene and acetone) ethylene glycol monoethyl ether welding perchloroethylene mercury vapor heat military radar high levels of kepone high levels of bromine vapor high levels of radiation carbon disulfide 2,4-dichlorophenoxy acetic acid (2,4-d) exposure to occupational hazards can impact: number of sperm. some reproductive hazards can stop or slow the actual production of sperm. this means that there will be fewer sperm present to fertilize an egg; if no sperm are produced, the man is sterile. if the hazard prevents sperm from being made, sterility is permanent. sperm shape. reproductive hazards may cause the shape of sperm cells to be different. these sperm often have trouble swimming or lack the ability to fertilize the egg. sperm transfer. hazardous chemicals may collect in the epididymis, seminal vesicles, or prostate. these chemicals may kill the sperm, change the way in which they swim, or attach to the sperm and be carried to the egg or the unborn child. sexual performance. changes in amounts of hormones can affect sexual performance. some chemicals, like alcohol, may also affect the ability to achieve erections, whereas others may affect the sex drive. several drugs (both legal and illegal) have effects on sexual performance, but little is known about the effects of workplace hazards. sperm chromosomes. reproductive hazards can affect the chromosomes found in sperm. the sperm and egg each contribute 23 chromosomes at fertilization. the dna stored in these chromosomes determines what someone will look like and their our bodies will function. radiation or chemicals may cause changes or breaks in the dna. if the sperm's dna is damaged, it may not be able to fertilize an egg; or if it does fertilize an egg, it may affect the development of the fetus. some cancer treatment drugs are known to cause such damage. however, little is known about the effects of workplace hazards on sperm chromosomes. pregnancy. if a damaged sperm does fertilize an egg, the egg might not develop properly, causing a miscarriage or a possible health problem in the baby. if a reproductive hazard is carried in the semen, the fetus might be exposed within the uterus, possibly leading to problems with the pregnancy or with the health of the baby after it is born.