FETAL DEVELOPMENT

Peggy Pannell RN, MSN

Learning Goals• Normal Fetal Development

– From ovulation to birth

• Teratogen – Definition and potential effects on

development

Vocabulary• Blastocyst• Conception• Ductus arteriosus• Embryo• Fertilization• Fetus • Foramen Ovale• HCG• Implantation

• L/S ration• Gestational age• Vernix• Zygote• Placenta• Quickening• Surfactant• Teratogens• Umbilical Cord

FERTILIZATION

• Begins with 46 pair of chromosomes, splits off to 23 then combine for a unique new 46 pair.

Stages and Time Frames

• Ovum • Zygote • Morula • Blastocyst • Embryo • Fetus (Oh, Zee my baby eats fast)

IMPLANTATION

First weeks of human development:Blastocyst embedded in endometrium.

PRIMARY GERM LAYERS

• Ectoderm• Mesoderm• Endoderm

GESTATIONAL AGE• Gestational age=Time since last menstrual period

(LMP)• EDC, EDD, EDB• 266 Days after fertilization• 280 Days after onset of LMP

Fertilization LMPDays 266 280Weeks 38 40Calendar Months 8 3/4 9

Lunar Months 9 1/2 10

GESTATIONAL AGE

Nagele’s Rule• Add 7 days to the first day of the last

normal menstrual period, subtract 3 months and add 1 year.

• Example: – 1st day of LNMP=December 16 2006– add 7 days = Dec. 23 2006 – subtract 3 months = Sept 23 2006– add 1 year =Sept 23 2007, estimated due date

(EDD)

TRIMESTERSTrimester1st = week’s 1-13

2nd = week’s 14 - 26

3rd = week’s 27 and on

(38-40 WEEKS)

STAGES OF DEVELOPMENT

FETAL MEMBRANES

• Amnion• Chorion

Decidua capsularis

Decidua basalis

Developing placenta

Yolk sac

Amniotic cavity

Intrauterine cavity

Decidua veraMucus plug(operculum)Mucus plug(operculum)

Chorion (blends with placenta)

Amnion (blends with umbilical cord)

Membranes:

Umbilical cord (funis)

Villi of fetal portion of placenta filled with fetal blood

Decidua capsularis

Decidua basalis

Developing placenta

Yolk sac

Amniotic cavity

Intrauterine cavity

Decidua veraMucus plug(operculum)Mucus plug(operculum)

Chorion (blends with placenta)

Amnion (blends with umbilical cord)

Membranes:

Umbilical cord (funis)

Lacunae in decidua basalis filled with maternal blood

Intrauterine cavity

Decidua capsularis

Decidua vera

1 Month • First Trimester

At the end of four weeks: • Baby is 1/4 inch in length • Heart, digestive system, backbone and spinal cord begin to

form • Placenta (sometimes called "afterbirth") begins to develop • The single fertilized egg is now 10,000 times larger than

size at conception

Month 2 • First Trimester

At the end of 8 weeks: • Baby is 1-1/8 inches long • Heart is functioning • Eyes, nose, lips, tongue, ears and teeth are forming • Penis begins to appear in boys • Baby is moving, although the mother can not yet feel

movement

Month 3 • First Trimester

At the end of 12 weeks: • Baby is 2 1/2 to 3 inches long • Weight is about 1/2 to 1 ounce • Baby develops recognizable form. Nails start to develop and earlobes are

formed • Arms, hands, fingers, legs, feet and toes are fully formed • Eyes are almost fully developed • Baby has developed most of his/her organs and tissues • Baby's heart rate can be heard at 10 weeks with a special instrument

called a Doppler

Month 4 • Second Trimester

At the end of 4 months: • Baby is 6 1/2 to 7 inches long • Weight is about 6 to 7 ounces • Baby is developing reflexes, such as sucking and swallowing and may

begin sucking his/her thumb • Tooth buds are developing • Sweat glands are forming on palms and soles • Fingers and toes are well defined • Sex is identifiable • Skin is bright pink, transparent and covered with soft, downy hair • Although recognizably human in appearance, the baby would not be able

to survive outside the mother's body

Month 5 • Second Trimester

At the end of 5 months: • Baby is 8 to 10 inches long • Weight is about 1 pound • Hair begins to grow on baby's head • Soft woolly hair called lanugo will cover its body. Some may

remain until a week after birth, when it is shed. • Mother begins to feel fetal movement • Internal organs are maturing • Eyebrows, eyelids and eyelashes appear

Month 6

• Second TrimesterAt the end of 6 months:

• Baby is 11 to 14 inches long • Weight is about 1 3/4 to 2 pounds • Eyelids begin to part and eyes open sometimes for short

periods of time • Skin is covered with protective coating called vernix • Baby is able to hiccup

Month 7

• Third TrimesterAt the end of 7 months:

• Baby is 14 to 16 inches long • Weight is about 2 1/2 to 3 1/2 pounds • Taste buds have developed • Fat layers are forming • Organs are maturing • Skin is still wrinkled and red • If born at this time, baby will be considered a premature baby and

require special care•

Month 8 • Third Trimester

At the end of 8 months: • Baby is 16 1/2 to 18 inches long • Weight is about 4 to 6 pounds • Overall growth is rapid this month • Tremendous brain growth occurs at this time • Most body organs are now developed with the exception of the lungs • Movements or "kicks" are strong enough to be visible from the outside • Kidneys are mature • Skin is less wrinkled • Fingernails now extend beyond fingertips

Month 9Third Trimester

At the end of 9 months: • Baby is 19 to 20 inches long • Weight is about 7 to 7 1/2 pounds • The lungs are mature • Baby is now fully developed and can survive outside the

mother's body • Skin is pink and smooth • Baby settles down lower in the abdomen in preparation for

birth and may seem less active

AMNIOTIC FLUID• Clear, yellowish fluid surrounding the

developing fetus.• Average amount 1000 ml.• Having < 300ml – Oligohydramnios,

associated with fetal renal abnormalities.

• Having > 2 L – Hydramnios, associated with GI and other malformations.

AMNIOTIC FLUID• Protects Fetus• Controls Temperature• Supports Symmetrical Growth• Prevents Adherence to amnion• Allows Movement• Source of oral fluid• Acts as a excretion-collection

repository

UMBILICAL CORDConnecting link between fetus and

placenta.• Transports oxygen and nutrients to fetus

from the placenta and returns waste products from the fetus to the placenta.

• Contains: 2 arteries and 1 vein supported by mucoid material (wharton’s jelly) to prevent kinking and knotting.

• Contains NO pain receptors.

PLACENTA

PLACENTA

MOM

Baby

Schematic drawing of placenta: how it supplies oxygen and nutrition to embryo and removes waste products. Deoxygenated blood leaves fetus through the umbilical arteries and enters placenta, where it is oxygenated. Oxygenated blood leaves placenta through the umbilical vein, which enters the fetus via the umbilical cord

Baby

mom

PLACENTAProduce protein hormones:• Human chorionic gonadotrophin

(HCG)- 8-10 days past conception, is basis for pregnancy test

• Progesterone• Estrogen• Human Placental Lactogen

PLACENTA• Sieve/filter – allows smaller particles

through and holds back larger molecules. Passage of materials in either direction is effected by:– Diffusion: gases, water, electrolytes– Facilitated transfer: glucose, amino

acids, minerals.– Pinocytosis: movement of minute

particle

PLACENTA• Mother transmits immunoglobulin G

(IgG) to fetus providing limited passive immunity.

• Leakage: caused by membrane defect: may allow maternal and fetal blood mixing.

VIABILITY• Capability of

fetus to survive outside uterus at the earliest gestational age - 22-24 weeks

• Survival depends on:– Maturity of fetal

central nervous system

– Maturity of lungs

RESPIRATORY SYSTEM• Terminal SAC period - 24 Weeks to birth• Growth of primitive alveoli• Pulmonary surfactants

produced which act as wetting agents that prevent alveolar walls from sticking

• Insufficient surfactant - RDS

• Lecithin/Sphingomyelin-Phospho LipidsL/S Ratio

30-32 Weeks 1.2 : 135 Weeks 2:1 (MATURITY)

CARDIOVASCULAR SYSTEM

• 1st System to function

• FHR 120-160/Min• Can hear FHR

with doppler at 10-12 Weeks

FETAL CIRCULATION• Arteries in umbilical

cord and fetal body carry deoxygenated blood.

• Vein in cord and those in fetal body carry oxygenated blood

• Ductus venosus connects umbilical vein and inferior vena cava; bypassing portal circulation.

FETAL CIRCULATION• Foramen Ovale

allows blood to flow from right to left atrium, bypassing lungs.

• Ductus Arteriosus allows blood flow from pulmonary artery to aorta, bypassing fetal lungs;

• HEPATIC SYSTEM– Liver functions 4-6 weeks– Full liver function after delivery

• MUSCULO-SKELETAL SYSTEM– Bones and muscles develop by 4th week– Fontanels – areas where >2 bones meet– 7-8 Weeks arms & leg movements

GASTROINTESTINAL SYSTEM

• Forms during 4th week• Middle portion of the

intestine projects out into cord during 5th week. Returns during 10th week. If this does not occur- Omphalocele present at birth

• Meconium – Dark green to black tarry waste accumulated in the fetal intestine near term

RENAL SYSTEM

• Kidneys form in 5th week and begin to function 4 weeks later.

• Voiding into amniotic fluid• Low volume can show renal dysfunction• Renal malformation can be diagnosed

in utero. • GFR is low at birth

NEUROLOGICAL SYSTEM

• Formed from the ectoderm during the 3rd week

• Respiratory effort 18 1/2 WKS• Swallowing 12 1/2 WKS• Sucking 29 WKS• Fetal movement felt 16-20

WKS (Quickening)

ENDOCRINE SYSTEM

• Thyroid gland 1st to develop• Insulin produced at 20 weeks

INTEGUMENTARY SYSTEM• 7th week – Two layers of cells• Vernix caseosa –Protects skin• Lanugo – Fine hair• 10th week – Fingernails, toenails

IMMUNE SYSTEM

• Passive immunity - FROM MOM

• Active immunity - FROM FETUS

MULTIFETAL PREGNANCY

• TWINS• MULTIFETAL

PREGNANCIES

Teratogens• Environmental exposures that can

adversely effect the developing fetus– Maternal Conditions

• Alcoholism, Diabetes, Endocrinopathies, Phenylketonuria (PKU), Smoking, Nutritional problems

– Infections Agents• Rubella, Toxoplasmosis, Syphillis, Herpes Simplex,

Cytomegalic Inclusion Disease, Varicella, Venezuelan Equine Encephalitis

– Mechanical Problems (deformations)• Amniotic band constrictions, Umbilical Cord

constraint, Disparity in uterine size and uterine contents

– Chemicals, drugs, radiation, hyperthermia

STAGES OF DEVELOPMENT