The Growing Fetus

The fetus is the infant during intrauterine life.

Nursing Process:

Assess - predictable stages of development that are used for guidelines for the
expected date of birth.

Plan - goals and outcome criteria

Implement - teaching parents about fetal growth and development at their
level

Evaluation - if changes are made
Stages of Fetal Development

In 38 weeks a fertilized egg matures from a single cell carrying all necessary
genetic material to fully developed fetus ready to be born.

Terms:

Ovum - from ovulation to fertilization

Zygote - from fertilization to implantation

Embryo - from implantation to 5-8 weeks

Fetus - from 5-8 weeks until term

Conceptus - developing embryo or fetus and placental structures throughout
pregnancy

Fertilization: The beginning of pregnancy.

Fertilization is the union of the ovum and a spermatozoon.(conception,
impregnation or fecundation).

Fertilization occurs in outer 3rd of a fallopian tube, the ampullar portion.

Fertilization has a span of 72 hours (48 hours before ovulation plus 24 hours
afterwards).

Ovum and surrounding cells are propelled into fallopian tube by cilia.

One ovum reaches maturity each month.

Ovum is capable of fertilization for only 24 hours (48 at the most).

Sperm reach the ovum and clusters around the protective layer of corona
cells.

Hyaluronidase (proteolitic enzyme) is released by sperm and acts to dissolve
the layer of protective cells.

One sperm is able to penetrate the cell membrane of the ovum.

Once it penetrates the zona pellucide the membrane becomes impervious to
sperm.

(Except in the formation of hydatidiform mole > abnormal growth).
Next the chromosomal material of ovum and sperm fuse and become a
zygote.

23 chromosomes each = 46 total

Fertilization depends on:

maturation of both sperm and ovum

ability of sperm to reach the ovum

ability of sperm to penetrate the zona pellucida and cell membrane and
achieve fertilization.

From the fertilized ovum (zygote) the future child and accessory structures
needed for support during intrauterine life, such as the placenta, fetal
membranes, amniotic fluid, and umbilical cord, are formed.

Implantation:

zygote migrates toward body of the uterus.

takes 3 to 4 days

during this time mitotic cell division, or cleavage, begins.

1st cleavage occurs at about 24 hours.

continues at a rate of one every 22 hours.

the zygote reaches the body of uterus with about 16 to 50 cells.

bumpy appearance termed morula.

Morula continues to multiply as it floats free in the uterine cavity for 3 to 4
days.

Large cells collect leaving a fluid space surrounding an inner cell mass and is
termed blastocyte.

This attaches to the uterine endometrium.

Trophoblast - cells in the outer ring.

Embryoblast - inner cell mass later forms the embryo.

Implantation occurs in 8 to 10 days after fertilization.

The blastocyte brushes against the rich endometrium (in secretory phase of
menstrual cycle) termed - apposition

attaches to the surface of the endometrium - adhesion

proteolytic enzymes dissolve tissues

settles down (burrows) into soft folds - invasion

usually high posterior side of the uterus

if low = placenta previa

50% of zygotes never achieve this.

A pregnancy ends in 8 to 10 days after fertilization, before the woman is
aware of a pregnancy.

Vaginal spotting may occur with adhesion / invasion due to rupture of
capillaries by the implanting trophoblast cells.

Once implanted the zygote is called an embryo.
Embryonic and Fetal Structures

Decidua: (falling off)

uterine endometrium grows in thickness and vascularity.

Will be discarded after the birth of the child.

3 areas:

decidua basalis - directly under the embryo

decidua capsularis - stretches or encapsulates the surface of trophoblast

decidua vera - remaining portion of lining

Embryo grows and pushes decidua capsularis like a blanket, enlargement,
contacts opposite uterine wall, fuses with endometrium.

At birth this entire inner surface of the uterus is stripped away, leaving the
organ highly susceptible to hemorrhage and infection.

Chorionic Villi:

Once implantation is achieved, trophoblastic layer of cells of blastocyst begins
to mature rapidly.

11th to 12th day miniature villi reach out from trophoblast into endometrium.

Central core of connective tissue contain fetal capillaries.

Syncytial layer produces hormones, hCG, HPL, estrogen, progesterone.

Placenta: (latin for pancake)

arises out of trophoblast tissue.

serves as fetal lungs, kidneys, GI, endocrine

growth parallels fetal growth: 15 to 20 cm in diameter and 2 to 3 cm in depth
at term.

covers about 1/2 the surface of internal uterus

Circulation:

12 th day of pregnancy maternal blood begins to collect

by 3rd week-oxygen, nutrients, fluid diffuse from mother through chorionic villi
to villi capillaries to the developing embryo.

no direct exchange of blood between embryo and mother during pregnancy.

exchange is by selective osmosis through the chorionic villi.

Minute breaks do occur

membrane is affected by maternal B/P, pH of fetal and maternal plasma.

Cotyledon:

in a mature placenta there are about 30 separate segments. (networked)

100 maternal uterine arteries supply the mature placenta.

blood flow through the placenta is about 50 mL/min. at 10 weeks to 500 to
600 mL/min at term.

To accommodate increased blood flow arteries increase in size.

Mothers heart rate, total cardiac output, and blood volume increase to supply
the placenta.

Uterine perfusion:

placental circulation is most efficient when mother lies on her left side.

This lifts the uterus away from the inferior vena cava,preventing blood from
being trapped in lower extremities.

If the mother lies on her back the weight of the uterus on vena cava causes
supine hypotension.

At term a placenta weighs 400 to 600g 1 lb.

A small or enlarged placenta suggests circulation to the placenta is
compromised.

Women with diabetes may develop a larger than usual placenta from fluid
collected between cells.
Endocrine Function

Human Chorionic Gonadotropin:

1 st hormone to be produced.

found in maternal blood and urine shortly after implantation or first missed
period for 100 days from trophoblast.

analyzed with urine pregnancy test.

negative within 1 to 2 weeks post delivery.

hCG functions to keep corpus luteum producing progesterone, if this fails or
progesterone falls the endometrium will slough,

until 8th week outer layer of cells of placenta begins to produce
progesterone.

hCG suppresses maternal immunologic response to not reject the placenta.

Estrogen:

primarily estriol is produced as a second product of syncytial cells of placenta.

contributes to mammary gland development in preparation for lactation.

stimulates uterine growth to accommodate fetus.

assessing amount of estriol in maternal serum was used to test fetal well
being.

Progesterone:

maintains endometrial lining of the uterus during pregnancy.

present in serum 4th week of pregnancy.

reduces contractility of uterine muscle during pregnancy(prevents premature
labor)

Human Placental Lactogen: (HPL)

both growth-promoting and lactogenic properties.

produced by the placenta by 6th week of pregnancy and increases to peak at
term.

it promotes mammary gland growth in preparation for lactation in the mother.

regulates maternal glucose, protein, and fat levels so adequate amounts are
available to the fetus.
Umbilical Cord

Formed from the amnion and chorion and provides a circulatory pathway
connecting the embryo to the chorionic villi.

Function is to transport oxygen and nutrients to the fetus from the placenta
and to return waste products from the fetus to the placenta.

21 inches (53cm) long and 3/4 inch (2cm) thick.

One vein - carries blood from placental villi to the fetus.

2 arteries - carrying blood from the fetus back to the placenta villi.

Wharton’s jelly - gelatinous mucopolysaccharide gives cord body and prevents
pressure on the vein and arteries.

The outer surface is covered with amniotic membrane.

Blood can be withdrawn from the umbilical vein or transfused into the vein
during intrauterine life for fetal assessment or treatment.

Rate is rapid 350 mL/min. at term.

Blood flow (blood velocity) can be determined by ultrasound.

The rapid rate of blood flow through the cord makes it unlikely that it will twist
or knot enough to interfere with O2 supply.

20% of births a loose loop of cord is found around the fetal neck (nuchal
cord).

Smooth muscle is abundant in the arteries of the cord.

Constriction of muscles after birth

contributes to hemostasis and helps prevent hemorrhage of the newborn
through the cord.

The cord contains no nerve supply, so it can be cut at birth without discomfort
to child or mother.
Membranes and Amniotic Fluid

The chorionic villi on medial surface of the trophoblast gradually thin and leave
the medial surface smooth this becomes chorionic membrane, the outer most
fetal membrane - next to baby.

Once it becomes smooth, it offers support to the sac that contains the
amniotic fluid.

The amniotic membrane (amnion) forms beneath the chorion and becomes
adherent to the fetal surface of the placenta, and give that surface a typically
shiny appearance.

no nerve supply: no pain when it ruptures.

Amniotic membrane acts to support and produce amniotic fluid.

It produces a phospholipid that initiates the formation of prostaglandins which
cause uterine contractions and maybe the trigger to initiate labor.

amniotic fluid is constantly being newly formed and reabsorbed, so it is never
stagnant within the membranes.

Fetus continually swallows the fluid, it is absorbed across the fetal intestine
into the fetal bloodstream.

Umbilical arteries exchange it across the placenta. Also by direct contact with
fetal surface of the placenta.

At term amniotic fluid is 800 to 1,200 mL.

Excessive amniotic fluid-hydramnios (>2,000mL) this occurs in women with
diabetes R/T hyperglycemia (fluid shift into amniotic space).

Reduction in the amount of amniotic fluid - oligohydramnios (<300) a
disturbance of kidney function).

alkaline pH 7.2

Protective:

shields against pressure or blow to mother’s abdomen.

protects fetus from changes in temperature.

aids in muscular development with allowing movement.

protects cord from pressure, protecting fetal oxygenation.
Origin and Development
From the beginning of fetal growth, development proceeds in a

cephalocaudal (head to toe) direction.

Head first then middle and then lower body parts. This continues after birth
also.

Body organ systems develop from specific tissue layers called germ layers.

Primary Germ Layers:

At the time of implantation, the blastocyte has separated to two cavities in the
inner structure.

Amniotic cavity (large) - lined with a distinctive layer of cells called - Ectoderm.

Smaller cavity yoke sac which is lined with entoderm which supplies
nourishment only until implantation. After that, it provides a source of red
blood cells until the hematopoietic system is mature.

Ectoderm - CNS, PNS, skin, hair ,nails, sebaceous glands, sense organs,
mucus membranes of the mouth, anus, nose, tooth enamel, mammary glands

Mesoderm (middle layer)

support structures - bone cartilage, muscle, ligament, tendon. Dentin of
teeth, kidneys, ureters, reproductive system, heart, circulatory system,
blood cells, lymph cells.

Entoderm (yolk sac)

lining of pericardia, pleura peritoneum, GI tract, respiratory tract, tonsils,
parathyroid, thyroid, thymus, bladder,and urethra.

Each germ layer of primary tissue develops into specific body systems.

One reason rubella infection is so serious in pregnancy is because the virus is
capable of affecting all the germ layers.

All organ systems are complete at 8 weeks’ gestation (end of the embryonic
period).

Organogenesis: (organ formation)

The growing structure is most vulnerable to invasion by teratogens.
Cardiovascular System

One of the 1st systems to become functional in intrauterine life.

Simple blood cells joined to the walls of the yolk sac progress to a network of
blood vessels and to a single heart tube forming as early as the 16th day of
life, beating at 24th day, the septum divides during the 6th or 7th week,
heartbeat may be heard with a doppler at 10th to 12th week.

After the 28th week the heart rate begins to show a baseline variability of 5
beats/min.

Fetal Circulation:

As early as the 3rd week of intrauterine life, fetal blood has begun to
exchange nutrients with maternal circ across the chorionic villi.

Fetus derives O2 and excretes CO2 from the placenta (not lungs).

Blood enters the cells of lungs.

Specialized structures in the fetus shunt blood flow to brain, liver, heart,and
kidneys.

Blood from the placenta is highly oxygenated.

Blood enters through the umbilical vein (called vein because the direction of
blood flow is toward the fetal heart).

Carries blood to inferior vena cava through accessory structures - ductus
venosus.

It receives O2 blood from the unbilical vein to supply the fetal liver.

Then, empties into the inferior vena cava.

From the inferior vena cava blood is carried to the right side of the heart.

As blood enters right atrium the bulk is shunted into the left atrium through an
opening in the atrial septum the foremen ovale.

From the left atrium it follows normal circ. into the left ventricle and into the
aorta.

Deoxygenated blood from the body is returned to the heart by the vena cava.

The blood enters the right atrium and leaves by the normal circ. route.

A large portion of this blood is shunted away from the lungs through an
additional structure - ductus arteriosus which is directly into the aorta and
then the descending aorta.

Most of the blood flow from the descending aorta is transported by the
umbilical arteries (arteries even though they are transporting deoxygenated
blood because they are carrying blood away from the heart).

back through the umbilical cord to the placenta villi, where new O2
exchange takes place.

O2 saturation of the fetus is about 80% of the newborn’s saturation level.

Fetal heart rate - 120 to 160 beats/ min. is necessary to supply O2 to cells
when RBC’s are never fully saturated.

CO2 does not accumulate because of rapid diffusion into maternal blood
across a favorable placental pressure gradient.

Fetal Hemoglobin:

has a different composition

2 alpha and 2 gamma chains compared with 2 alpha and 2 beta chains in
adults.

Fetal hemoglobin has greater O2 affinity and is more concentrated.

Hemoglobin at birth - 17.1 g/100ml

Hematocrit - 53%

Sickle cell anemia - beta hemoglobin chain, symptoms do not appear for 6
months because hemoglobin matures then.
Respiratory System

At the 3rd week respiratory and digestive tracts exist as a single tube.

Initially it is solid then canalizes.

Week 4 a septum begins to divide the esophagus from the trachea.

Week 6 lung buds may extend down into the abdomen.

Week 7 diaphragm becomes complete.

Week 24 and 28 - alveoli and capillaries begin to form. Both must be
developed before gas exchange can occur in the fetal lungs.

Spontaneous respiratory begin at 3 months.

Specific lung fluid with low surface tension and low viscosity forms in alveoli to
aid in expansion of alveoli at birth.

Surfactant a phospholipid substance is formed and excreted by aveolar cells
about 24th week. This decreases alveolar surface tension on expiration,
preventing alvolar collapse and improves respirations outside.

Surfactant has 2 components:

lecithin - 35th week increased production

sphingomyelin - early formation of surfactant

Surfactant mixes with amniotic fluid (L/S).

Lack of surfactant is a factor with RDS.

Interference of blood supply to the fetus causes increased production of
surfactant.

Hypertension > increases stress increases steroid level associated with
alveolar maturation.
Nervous System

Week 3 and 4 formation begins.

Neural plate - a thickened portion of the ectoderm is apparent by 3rd week.
Its top portion differentiates into the neural tube, which will form the CNS
(brain and spinal cord), the neural crest, which develops into the peripheral
nervous system.

Week 8 - brain waves can be detected on EEG.

All parts of the brain form in utero and growth continues after birth.

Eye and inner ear develop as projections of the original neural tube.

Week 24 ear is capable of responding to sound

Eyes exhibit a pupillary reaction.

Very vulnerable to anoxia during the early weeks of the embryonic period, all
during pregnancy and at birth.
Endocrine System

As soon as endocrine organs mature intrauterine life, function begins:

Adrenal glands supply a precursor for estrogen synthesis by the placenta.

Pancreas produces insulin needed by the fetus(does not cross the placenta
from mother to fetus).

Thyroid and parathyroid glands play a vital role in metabolic function and
calcium balance.
Digestive System

Week 4 digestive tract is separated from the respiratory tract.

Grows rapidly from solid to a tube by canalization.

Endothelial cells of the GI tract proliferate, this occludes the lumens.

Intestines remain in the base of the cord until 10th week, then after
abdominal cavity growth the intestine returns to the abdominal cavity.

Must rotate 180 degrees.

16th week meconium forms in the intestines

meconium consists of cellular wastes, bile fats, mucoproteins,
mucopolysaccharides, portions of the vernix casosa, lubricating substances
that form on the fetal skin.

It’s black or dark green and sticky.

GI tract is sterile before birth.

Vitamin K is synthesized by action of bacteria in the intestines. This causes low
levels of vitamin K in newborns.

Week 32 or the fetus weighs 1,500 g sucking and swallowing reflexes.

Week 36 the ability of the GI tract to secrete enzymes essential to
carbohhydrate and protein digestion.

Amylase is not mature until 3 months after birth.

Lipase may not have developed yet.

Liver is active throughout gestation.

It functions as a filter between
the incoming blood and fetal circulation

deposit for stores of iron and glycogen, this is immature at birth.

This leads to hypoglycemia and hyperbilrubinemia in the first 24 hours after
birth.
Musculoskeletal System

Week 11 fetus can be seen to move on ultrasound (mother does not feel it
yet)

Week 20 quickening - movement of the fetus.

Week 12 ossification of bone tissue begins and continues until adulthood.
Reproductive System

A child’s sex is determined at conception.

Week 6 gonads form (ovaries or testes).

If testosterone is present male organs develop.

If absence of testosterone femal organs develop.
Urinary System

Rudimentary kidneys are present by 4th week but are not essential before
birth.

Week 12 urine is formed and excreted into the amniotic fluid by week 16.

At term fetal urine is 500mL/day.

The Loop of Henle is not fully differentiated until birth.
Integumentary System

Skin of a fetus is thin and almost translucent until subcutaneous fat begins to
be deposited about week 36.

Skin is covered by soft downy hairs (Lanugo) and a cream cheese like
substance vernix casosa, which is important for lubrication and keeping the
skin from macerating.
Immune System

IgG maternal antibodies cross the placenta into the fetus at 3rd trimester,
giving temporary passive immunity.

Poliomyelitis, rubella, rubeola, diptheria, tetanus, mumps, pertussis. Not
herpes.

Passive immunity peaks at birth and decreases over the next 8 months. At 2
months already has declined substantially.

Diphtheria, tetanus, pertussis, poliomyelitis, H influenzae are started soon
after birth.

Measles last over 1 year.

IgA and IgM antibodies cannot cross the placenta, if present the fetus was
exposed to the disease.
Milestones of Fetal Growth and Development
Determination of Estimated Birth Date

It is impossible to predict the day of birth.

Estimated date of birth - EDB, EDD or EDC.

280 days - 38 to 42 weeks in length.

Nagele’s rule:

1st day of last menstrual period.

Count back 3 months and add 7 days.

Normal variations - if ovulation and fertilization occurs early or late in the
menstrual cycle the pregnancy may be 2 weeks before or 2 weeks after the
EDD.
Fetal Growth and Development

Assessment:

Nurses responsibility

signed consent form with information on the procedure and possible risks

scheduling the procedure

explaining the procedure to the woman and support person

preparing the woman physically and psychologically

providing support during the procedure

assessing both fetal and maternal responses to procedures

provide follow up care

manage equipment and specimens

Estimated Fetal Growth:

McDonald’s rule - method of determining, during mid pregnancy, that the
fetus is growing in utero by measuring fundal (uterine) height.

Distance from fundus to symphysis in centimeters is equal to the week of
gestation between week 20 to 31.

Measure from the notch of the symphysis pubis to over the top of the fundus
with woman lies supine.

This becomes inaccurate in 3rd trimester because the fetus is growing in wt.
than height.

Milestones:

12 weeks- over symphysis pubis

20 weeks at umbilicus

36 weeks xiphoid process
Assessing Fetal Well-Being:

Fetal movement - quickening week 18 to 20

peaks at week 28 to 38

healthy fetus moves 10 times a day.

Ask mother to lie in left recumbent position after a meal and record number of
fetal movements in next hour.

2 times in 10 minutes

fewer than 5 in 1 hour - notify the doctor.

Fetal Heart Rate:

120 to 160 beats per minute throughout pregnancy.

Week 10 to 11 heart sounds can be heard and counted with a doppler.

Rhythm Strip Testing:

baseline fetal heart rate per minute and long and short term variability.

Place woman in semi-fowlers (prevents supine hypotension syndrome).

Monitors are attached abdominally and recorded for 20 minutes (mother in
fixed position)

Short term variability- beat to beat variability- denotes small changes in rate
from second to second if parasympathetic nervous system is receiving
adequate O2 and nutrients.

Long term variability - denotes the differences in heart rate that occur over 20
minutes (fetus moves 2x/10 min) increases with movement.

This reflects fetal sympathetic nervous system.

Nonstress Testing:

measures response of fetal heart rate to movement.

Monitors are attached to abdomen

mother pushes a button attached to the monitor when she feels the fetus
move.

FHR should increase 15 beats/ min and remain elevated for 15 seconds.

Decreases when fetus quiets. If no increase is noticeable with movement poor
O2 perfusion of fetus id suggested.

Test lasts 10 to 20 minutes.

If no fetal movements in 20 minutes fetus may be sleeping.

Orange juice or carbohydrate may increase blood glucose level which
stimulate the fetus. Also loud noise may stimulate fetus.

Vibroacustic Stimulation:

Acustic stimulation (artificial larynx) applied to abdomen to produce a sharp
sound, startling and waking the fetus.

80 dB frequency of 80 Hz.

Contraction Stress Testing:

FHR is analyzed in conjunction with contractions.

Mother stimulates the nipple which releases oxytocin which initiates uterine
contractions

External uterine contraction and FHR monitors are applied

3 contractions with duration of 40 seconds or more present in a 10 minute
period.

Normal (negative) when no FHR decelerations are present with contractions.

Abnormal (positive) 50% or more contractions cause a late deceleration (dip
in FHR) toward the end of a contraction and continues after the contraction.

Woman waits 30 min after the test.

Ultrasound:

response of sound waves against objects.

Diagnose pregnancy at 6 weeks gestation

confirm presence, size, and location of placenta and amniotic fluid.

Establishes fetal growth, gross defects

Establish presentation and position (sex)

Predict maturity by biparietal diameter

Mother has to have a full bladder ( drink a full glass of water q 15 min. in 1
1/2 hours

Place a towel under the right buttock to tip uterus away from the vena cava.

Gel applied to abdomen (room temperature)

Transducer is applied intravaginal or abdominal

Biparietal Diameter:

measures side to side measurement of fetal head (8.5cm or more infant
weighs > 2500g 5.5 lb) 40 week gestation.

Also measures head circumference and femoral length.

Doppler Umbilical Velocimetry:

Measures velosity at which RBC and vessels are traveling.

Placental Grading:

amount of calcium deposits in base of placenta.

Amniotic Fluid Volume Assessment:

average index is 15 cm between 28-40 wks.

ECG at week 11 of pregnancy (inaccurate before week 20 because fetal
electrical conduction is week).

MRI used to diagnos ectopic pregnancy or trophoblastic disease.

Maternal Serum Alpha-Fetoprotein is a substance produced by the fetal liver
that is present in amniotic fluid and maternal serum. Begins to rise at week
11.

Detects Down Syndrome, open spinal or abdominal defects.

Triple Screening - analysis of 3 indicators:

Maternal serum Alpha-fetoprotein

unconjugated estriol

hCG

used for Downs syndrome

Chorionic Villi Sampling (CVS)

biopsy and analysis for chromosomal analysis done at week 10 to 12.

Amniocentesis:

aspiration of amniotic fluid from the uterus for examination.

Week 12 to 13

1 mL of fluid is needed

3 to 4 in 20 to 22 gauge spinal needle

woman rest for 30 minutes after the procedure

constant monitoring for FR and contractions

if Rh-neg. blood give RhoGAM

Amniocentesis:

color of water or slight yellow tinge


strong yellow- bilirubin

green- meconium
lecithin/ sphingomyelin ratio

protein components of lung enzyme surfactant that alveoli form week 2224

phosphatidyl glycerol and desaturated phosphtidylcoline


Bilirubin Determination


found in surfactant
must be blood free to analyze bilirubin
Chromosome Analysis

uses fetal skin cells for karyotyping

Fetal Fibronectin

glycoprotein that helps placenta attach to the uterine decidua ( preterm
labor).

Inborn Errors of Metabolism

inherited diseases from inborn errors

Alpha-Fetoprotein

Percutaneous Umbilical Blood Sampling

aspiration of blood from the umbilical vein for analysis

Amnioscopy

visual inspection of amniotic fluid through the cervix and membranes with a
small fetoscope (detects meconium).

Fetoscopy

visualizing the fetus with fetoscope

confirms intactness of spinal column

biopsy of fetal tissue and blood sample

surgery

photos

done week16 to17 at the earliest

risks-premature labor, infection

Biophysical Profile (fetal Apgar)

combines 4 to 6 parameters into one assessment.

fetal movement and breathing, fetal tone, amniotic fluid volume, placental
grading fetal heart reactivity.

more accurate in predicting well being than any single assessment.

a score of 4 to 6 denotes a fetus in jeopardy.