Prenatal Development and
Birth
Chapter 19
Conception and Implantation
• Fertilization –
– The union of a male sperm cell and a female egg cell
in the fallopian tube** (conception)
– Resulting cell is called a zygote
• Within a day after the zygote forms, it begins
dividing as it travels down the fallopian tube.
• By the time it reaches the uterus, the zygote has
divided many times to form a cluster of cells with
a hollow space as the center.
Conception and Implantation
• Within a few days, the zygote attaches to
the uterine wall (implantation)
• The cluster of cells that develop between
the third and eighth weeks of pregnancy –
– Embryo (usually the 5th week**)
• After about the eighth week, this
developing groups of cells is called –
– Fetus
Embryonic Growth
• As the embryo grows, its cells continue to
divide, forming three tissue layers:
– Respiratory and digestive system
– Muscles, bones, blood vessels and skin
– Nervous system, sense organs and mouth
Embryonic Growth
• During this time, two important structures form
outside the embryo:
– Amniotic sac: a thin, fluid-filled membrane that
surrounds and protects the developing embryo. It also
insulates embryo from temperature changes.
– Umbilical cord: ropelike structure that connects the
embryo and the mother’s placenta.
• The placenta is a thick, blood-rich tissue that lines the walls
of the uterus during pregnancy and nourishes the embryo.
• Blood supply of the mother and developing
embryo are kept separate, materials still
diffuse from one blood supply to the other
through the umbilical cord.
– Harmful substances such as tobacco, alcohol
or other drugs can cross the placenta and
harm the embryo
Fetal Development
• 0-14 weeks – First Trimester
• 15-28 weeks – Second Trimester
• 28-40 weeks (birth) – Third Trimester
• See Figure 19.2 in Textbook (pg. 488-489)
Stages of Birth
• Labor –
– The final stage of pregnancy in which the
uterus contracts and pushes the baby out of
the mother’s body
• Stage 1: Dilation
• Stage 2: Passage through birth canal
– Breech birth – baby enters the birth canal feet
or buttocks first
• Stage 3: Afterbirth (placenta)
Proper Nutrition During Pregnancy
• Calcium – helps build strong bones and teeth, as well as
nerves and muscles.
• Protein – helps form muscle and most other tissue.
• Iron – makes red blood cells and supplies oxygen to
cells.
• Vitamin A – aids in cell and bone growth and eye
development.
• Vitamin B complex – aids in forming nervous system.
• Folic acid – critical part of spinal fluid and helps close the
tube that contains the central nervous system.
**IMPORTANT THAT THIS BEGINS IN THE 2ND
TRIMESTER**
Proper Nutrition During Pregnancy
• Weight gain is expected (25-35 lbs.)
• Most only need an additional 300 calories
per day, though.
• Excess weight can be a health risk for
mother and baby
• Caffeine can increase risk of birth defects
or low birth rate
• Physical activity can be beneficial
Tobacco and Pregnancy
• It is estimated that smoking accounts for:
– 30% of low birth weight
– 14% of premature births
– 10% of infant deaths
• May also affect the growth, mental
development and behavior of child until 11
years old
• Secondhand smoke included in all this
Alcohol and Pregnancy
• Alcohol consumed during pregnancy
quickly passes through the umbilical cord
to the fetus.
• The fetus breaks down alcohol much more
slowly than an adult does, so the alcohol
level in the fetus’s blood can be higher
than that of the mother and remain higher
for a longer period of time.
Fetal Alcohol Syndrome
A group of alcohol-related birth defects that
includes both physical and mental
problems
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Mental retardation
Learning disabilities
Serious behavior problems
Slowed growth
Physical deformities including a small skull,
abnormal facial features, and heart defects
Medicines, Other Drugs, and
Pregnancy
• Using drugs can have serious consequences
– Birth defects
– Premature labor
– Miscarriage
• Even OTC medicines should only be taken with the
approval of the doctor
• A baby can be born addicted to the drugs the mother
used during pregnancy.
• The infant will suffer withdrawal symptoms:
– hypersensitive and irritable and may cry for hours
– tremble and jerk
– May not bond with parents
Complications During Pregnancy
• Miscarriage – the spontaneous expulsion of a
fetus that occurs before the 20th week
• Stillbirth – dead fetus expelled from the body
after the 20th week
• Ectopic Pregnancy – zygote implants in the
fallopian tube, abdomen, the ovary or the cervix.
– Zygote can’t pass to the uterus
– STD could be a reason
– #1 cause of death of females in 1st trimester
Sterility
• Inability to reproduce
– Males: may be due to stress, drug use or
disease
– Females: may be due to blocked fallopian
tubes or severe scarring from STIs.