nursing

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

Days Weeks Calendar Months Lunar Months

Fertilization 266 38 8 3/4 9 1/2

LMP 280 40 9 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)

TRIMESTERS Trimester 1st = week’s 1-13 2nd = week’s 14 - 26 3rd = week’s 27 and on (38-40 WEEKS)

STAGES OF DEVELOPMENT

FETAL MEMBRANES Decidua basalis

• Amnion • Chorion

Developing placenta placenta Yolk sac Amniotic cavity Decidua capsularis Intrauterine cavity Decidua vera Mucus plug (operculum) Villi of fetal portion of placenta filled with fetal blood Intrauterine cavity Decidua capsularis Decidua vera

Lacunae in decidua basalis filled with maternal blood Umbilical cord (funis)

Membranes:

Amnion (blends with umbilical cord) Chorion (blends with placenta)

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 Trimester At 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 Trimester At 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 9 Third 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 CORD Connecting 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

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

PLACENTA Produce 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 Lipids L/S Ratio

30-32 Weeks 35 Weeks

1.2 : 1 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 occurOmphalocele 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