Chromosomal Abnormalities
One of the most common chromosomal abnormalities that can be detected during the prenatal period is Down Syndrome. Down Syndrome occurs at an incidence of 1/770 live births. It is a condition whereby there is an extra chromosome 21 (aka trisomy 21) that results in manifestations of cognitive difficulties, memory and speech problems, characteristic bodily and facial features, slow motor development, and increased incidences of diabetes, cardiac comorbidities, visual and hearing difficulties, gastrointestinal complications, Alzheimer’s disease, and an overall shortened lifespan. Down Syndrome risk increases with increasing maternal age, however 5-10% of cases have been found to contain extra genetic material originating from the father. Prenatal genetic screening is available for the detection of Down Syndrome and other chromosomal abnormalities through methods known as amniocentesis or chorionic villus sampling. There are other autosomal chromosomal abnormalities which do occur, however most result in spontaneous abortion or miscarriage.
If there is a chromosomal abnormality with one of the sex chromosomes, this is often not determined until adolescence, often the first sign being delayed puberty.
Teratogens
The term teratogen means “an environmental agent that causes damage during the prenatal period” and the consequences on a developing fetus are dependent upon the dose of teratogen, heredity, and fetal age. Most teratogens are damaging in the earliest stages of pregnancy (3-8 weeks after conception) however this is agent dependent. The addition of negative factors such as poor nutrition and lack of medical care can worsen the impact of a given teratogen on the fetus. Substances that may be considered teratogens include prescription and recreational drugs, alcohol, radiation, and environmental pollution.
An important prescription teratogen to be aware of for those who are childbearing age is a vitamin A derivative used to treat acne, known as Accutane or isotretinoin. First trimester exposure has been associated with abnormalities of the eyes, ears, bones, cardiovascular and immune systems, and importantly the brain in infants. It is recommended two forms of birth control be utilized if a woman is using Accutane. As well, antidepressant medications may be associated with premature delivery and birth complications. All pregnant women should consult their doctor regarding any prescription or nonprescription medications they wish to take while pregnant to ensure they are safe.
Illegal drugs such as cocaine or amphetamines cause infants to be born with a high risk of prematurity, low birth weight, and birth defects and unfortunately these children are born already addicted to the substances their mothers were using. This may cumulate into a difficult to care for infant for which struggling mothers are unable to consistently care for and longstanding behavioral problems may result. Cocaine may alter the early functioning of neurons and chemical balance in the brain of affected fetuses which can lead to cognitive, language, and impulse control difficulties. Marijuana use in pregnant mothers has been linked to future microcephaly, academic difficulties, and depression in affected fetuses. However, all of these findings are controversial and the precise damage of most illicit substance during the prenatal period is unknown.
Fortunately the incidence of smoking has decreased in recent decades, however some women continue to smoke throughout their pregnancy and the most widely associated prenatal effect is low birth weight infants. Some studies associate tobacco use during pregnancy with later behavioural problems in children, such as impulsivity and attention difficulties.
Fetal Alcohol Spectrum Disorder (FASD) occurs when an expecting mother consumes alcohol. It is unknown what amount of alcohol or at what stage in pregnancy its effects take place, thus physicians recommend women who are pregnant or intend to become pregnant avoid alcohol entirely. Children born with FASD display slowed physical growth, characteristic facial abnormalities such as short eyelids, thin upper lips, or flattened philtrums, and brain abnormalities, such as microcephaly (small head size). These are just some of the well recognized features of FASD, however alcohol use during pregnancy can result in many other defects within the sensory, cardiovascular, urinary, and immune systems. In adolescence and adulthood, FASD is associated with attention deficits, learning disorders, substance abuse, and depression.
Maternal Factors
The health of a pregnant mother directly influences that of their child, thus important factors impacting the developing mind include maternal nutrition, emotional stress, medical comorbidities, maternal age, and previous births, amongst others. In terms of nutrition, healthy weight gain during pregnancy is typically 25-35 pounds, this ensures the mother is consuming enough nutrients to fuel her body, as well as the fetus’. If the mother is malnourished during pregnancy this may result in serious consequences for the child’s central nervous system, such as microcephaly. This is especially true later in pregnancy when the energy demands of the fetus are higher and brain size is increasing rapidly. The type of nutrients pregnant mothers consume is also important, for example, folic acid supplementation reduces the risk of spina bifida or other neural tube defects by approximately 70%. Pregnant women should speak with their physician regarding folic acid supplementation from the time they begin planning to conceive and during the earliest stages of pregnancy.
Maternal stress can negatively impact a developing fetus because of the release of stress hormones, such as epinephrine and cortisol, into the shared blood system. This results in a rise in fetal heart rate, blood pressure, and glucose levels. If stress hormone levels are excessive and prolonged this can result in neurological deficits that heightens stress reactivity in later life. Thus, maternal stress has been associated with anxiety and aggression later in life. High levels of stress hormones also alter the immune system, predisposing those affected to infections.
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