Prenatal development
By the end of the tenth week of gestational age, the embryo has acquired its basic form and is referred to as a fetus.
This fetal period is described both topically (by organ) and chronologically (by time) with major occurrences being listed by gestational age.
[3] In many of the developing countries the starting point of this period is considered 28 completed weeks of gestation (or weight more than 1000 g).
When semen is released into the vagina, the spermatozoa travel through the cervix, along the body of the uterus, and into one of the fallopian tubes where fertilization usually takes place in the ampulla.
The term "conception" refers variably to either fertilization or to formation of the conceptus after its implantation in the uterus, and this terminology is controversial.
[5] The Y chromosome contains a gene, SRY, which will switch on androgen production at a later stage leading to the development of a male body type.
[6] The zygote spends the next few days traveling down the fallopian tube dividing several times to form a ball of cells called a morula.
A spontaneous abortion, or miscarriage, in the first trimester of pregnancy is usually[8] due to major genetic mistakes or abnormalities in the developing embryo.
During this critical period the developing embryo is also susceptible to toxic exposures, such as: The embryo passes through 3 phases of acquisition of nutrition from the mother:[9] The first ten weeks of gestational age is the period of embryogenesis and together with the first three weeks of prenatal development make up the first trimester of pregnancy.
The fetus starts producing leukocytes at 2 months gestational age, mainly from the thymus and the spleen.
[13] The first studies focused on the consequences of the famine to cognitive development, including the prevalence of intellectual disability.
[14] Such studies predate David Barker's hypothesis about the association between the prenatal environment and the development of chronic conditions later in life.
Many of these expecting mothers have little education and are therefore less aware of the risks of smoking, drinking alcohol, and drug use – other factors that influence the growth rate of a fetus.
[33][34] Some studies note that adolescent pregnancy is often associated with poverty, low education, and inadequate family support.
Recent research displays that there is a correlation between fine motor skills and prenatal risk factors such as the use of psychoactive substances and signs of abortion during pregnancy.
[40] Opioids including heroin will cause interrupted fetal development, stillbirths, and can lead to numerous birth defects.
The vasoconstriction of the effects of cocaine lead to a decrease in placental blood flow to the fetus that results in fetal hypoxia (oxygen deficiency) and decreased fetal nutrition; these vasoconstrictive effects on the placenta have been linked to the number of complications in malformations that are evident in the newborn.
[42] Prenatal methamphetamine exposure has shown to negatively impact brain development and behavioral functioning.
Study results showed that the prenatally exposed children performed lower on the intelligence measures than their non-exposed peers with ADHD.
The study results also suggest that prenatal exposure to methamphetamine may negatively impact processing speed as children develop.
[45] Exposure to secondhand smoke leads to higher risks of low birth weight and childhood cancer.
[48] Bacterial or parasitic diseases may also be passed on to the fetus, and include chlamydia, syphilis, tuberculosis, malaria, and commonly toxoplasmosis.
Mothers who gain less than 20 pounds during pregnancy are at increased risk for having a preterm or low birth weight infant.
[53] Low birth weight increases an infants risk of long-term growth and cognitive and language deficits.
Reilly (2017) states that stress can come from many forms of life events such as community, family, financial issues, and natural causes.
While a woman is pregnant, stress from outside sources can take a toll on the growth in the womb that may affect the child's learning and relationships when born.
Similar to stress, Reilly stated that in recent studies, researchers have found that pregnant women who show depressive symptoms are not as attached and bonded to their child while it is in the womb (2017).
[54] Exposure to environmental toxins in pregnancy lead to higher rates of miscarriage, sterility, and birth defects.
Prenatal exposure to mercury may lead to physical deformation, difficulty in chewing and swallowing, and poor motoric coordination.
[55] Exposure to high levels of lead prenatally is related to prematurity, low birth weight, brain damage, and a variety of physical defects.
