Stages of Prenatal development

First Trimester

• Germinal

• Embryonic

• Fetal

Germinal Period

• Duration is 2 weeks

• includes fertilization, formation of zygote, and implantation

• Structures that feed and protect the fetus begin to form

Amniotic fluid- regulates temperature and protects the baby from any sudden movements

Yolk sac- Produces blood cells until the necessary organs are mature enough to do so

Chorion - surrounds the amnion, finger-like villi emerge and attaches to the uterus, and the placenta forms acting as a bridge between the mother’s and fetus’ blood vessel. It is selectively permeable as it allows the transfer of nutrients from mother to baby and waste from mother to baby without their blood directly mixing.

Embryonic Period

• Duration occurs from implantation (third week) to the 8th week

• Forms three segments, ectoderm, mesoderm, and endoderm

The ectoderm consists of the nervous system and the skin, The mesoderm is responsible for the skeleton, muscles, and circulatory system. The endoderm creates the digestive system, lungs, urinary tracts, and glands.

Period of the embryo: fourth week. This 4-week-old embryo is only ¼-inch long, but many body structures have begun to form.

Second Month

Rapid growth continues with the formation of body parts such as limbs, fingers, and toes. Facial features and the neck also form. Internal organs such as the heart, liver, and spleen form and there is no longer a need for the yolk sac since the liver and spleen begin to produce the blood cells.

Period of the embryo: seventh week. The embryo’s posture is more upright. Body structures—eyes, nose, arms, legs, and internal organs—are more distinct. The embryo now responds to touch and can also move, although at less than one inch long and an ounce in weight, it is still too tiny to be felt by the mother

Fetal Stage

Duration: lasts from the ninth week up until birth

Period of the fetus: eleventh week. The fetus grows rapidly. At 11 weeks, the brain and muscles are better connected. The fetus can kick, bend its arms, open and close its hands and mouth, and suck its thumb. Notice the yolk sac, which shrinks as the internal organs take over its function of producing blood cells.

Muscles, organs, and the nervous system connect and become more organized, touch sensitivity spreads more across the body and the fetus moves more freely. The lungs start to contract and expand, breath rehearsals for outside of the womb. Genitals form and the sex can be identified. Finishing touches such as fingernails and eyelids form. The first trimester ends.

Second Trimester

• occurs between weeks 17-20

• A white, cheeselike substance called vernix forms on the fetus preventing chapping from being in the amniotic fluid

• White, downy hair called lanugo appears which helps the vernix stick to the skin.

• baby is at a decent size where it is felt by the mother

• Most of the brain’s neurons are already made, the glial cells that feed these neurons are still being created while the synapses are being created rapidly

• The fetus becomes sensitive to light and sound

• If the fetus is born during this stage, it will not survive

Third Trimester

The third trimester of pregnancy is a crucial period of fetal development and preparation for childbirth. During this time, the fetus grows rapidly and gains weight. The mother may experience discomfort due to the increasing size of the baby and the pressure on her organs. The baby's movements become more pronounced, and the mother can feel kicks and stretches. The lungs of the fetus mature, and the baby practices breathing movements. The baby's senses continue to develop, and they can hear sounds from the outside world. Towards the end of the third trimester, the baby settles into a head-down position in preparation for birth. The mother may experience Braxton Hicks contractions, which are practice contractions. Overall, the third trimester is a period of significant growth and development for both the mother and the baby.

Period of the fetus: twenty-second week. This fetus is almost one foot long and weighs slightly more than one pound. Its movements can be felt easily by the mother and by other family members who place a hand on her abdomen. If born now, the fetus has a slim chance of survival.

Period of the fetus: thirty-sixth week. This fetus fills the uterus. To nourish it, the umbilical cord and placenta have grown large. Notice the vernix (a cheeselike substance) on the skin, which protects it from chapping. The fetus has accumulated fat to aid temperature regulation after birth. In two more weeks, it will be full-term.

Teratogens

Refers to any environmental agent that causes damage during the prenatal period.

Types of Teratogens

• Dose - The dose of a substance can be a teratogen if it exceeds a certain threshold level. The severity and type of birth defects or abnormalities can vary depending on the dose and timing of exposure. Higher doses or prolonged exposure to teratogens generally increase the risk of adverse effects. It is important to note that the specific teratogenic effects of a substance can vary, and not all substances have the same potential to cause harm.

• Age- Age itself does not act as a teratogen. A teratogen is a substance or factor that can cause birth defects or developmental abnormalities in a fetus. However, advanced maternal age (typically defined as 35 years or older) is associated with an increased risk of certain birth defects and pregnancy complications. This is primarily due to factors such as genetic abnormalities in older eggs and a higher likelihood of pre-existing medical conditions. Women of advanced maternal age need to receive proper prenatal care and genetic counseling to minimize potential risks.

Drugs cause deformities starting at the embryonic stage with that stage being the most sensitive to teratogens.

Tobacco

• Low birth weight

• Miscarriage

• Premature Birth

Nicotine lessens blood flow to the uterus which causes the placenta to form abnormally lessening the amount of nutrients the body gets. It also creates carbon monoxide in both the mother’s and baby’s blood vessels. Oxygen in the blood vessel is replaced by carbon monoxide.

Alcohol

Diseases

• Fetal Alcohol Syndrome (FAS)

Characteristics

• Slow physical growth

• facial abnormalities

• brain injury

• Alcohol-related Neurodevelopment Disorder (ARND)

Effects

Reduction in size and damage to brain structures

Causes

• Oxygen is needed to metabolize alcohol which reduces the amount available to the fetus for cell growth.

• Hinders in the production and movement of brain neurons.

Radiation

• Prematurity

• Physical abnormalities

• Slow physical development