Fetal Physiology

fetal circulation

Fetal heart

Pumps blood through both the fetal circulation and the placenta

Youd think increased pressure load of the heart but Placenta acts as a large, low resistance vascular bed - allows blood to flow easily through circuit

Increased CO but not pressure load

Low stroke volume so required high heart rate 110-160

How does fetal blood flow change as it grows and demand increase?

Placenta becomes more vascularised increasing its capacity to exchange nutrients

Increase in FCO so that more blood is directed to the placenta over time

Cardiac growth and development

Initially Hyperplasia (increase in cell number)

32 weeks onwards - heart cells start to from 2 nuclei

after birth cells only get bigger not more (hypertrophy)

Pronephros

First Kidneys

Day 22

6-10 pair of tubules connected to the wolffian duct

non-function in humans

Mesonephros

5th- 11th week

Small amounts of urine produced

Humans develop about 40 mesonephric nephrons

Metanephros

Permanent kidney

starts week 5 - overlaps

Adult like nephrons which continue to branch until 36 weeks

urine produced from the 16th week - amniotic fluid

Amniotic fluid improtance

Breathed in by the fetal lung and helps with lung development

fetal kidney overall

born with all the nephrons we are ever going to have

nephrogenesis involved repeated branching events

disruption of these may theoretically halve nephron number

Affected by chemicals, stress and drugs

Fetal lung development timing

Surfactant

prevents the collaps eof alveoli during breathing

If not well enough developed causes - RDS in newborn

Fetal gastrointestinal system

Feces accumulated in the intestines from week 13

Liver makes RBC peaking at 16 weeks and continuing till term. many liver functions ae performed by placenta

Meconium

meconium consists of amniotic fluid, cellular debris, musus and bile

Fetal skin in embryonic period

Two layers

1. 1. periderm - sloughs off to form vernix

2. 2. inner basal layer - epidurmis and glands

Fetal skin

All layers of epidermis are present by week 20

preterm babies dont have vernix

causes water loss and poor temp control

Fetal brain

12-20 weeks form neurons that become nuclei

migrate to developing cortex and deep nuclei where they will reside for life

massive proliferation, differentiation of neurons and glia and organisation of brain regions

Biggest neural proliferation 8-15 weeks

Process in fetal brain formation

Synaptogenesis - connections between neurons

Apoptosis - selective neuronal loss

synaptic pruning - removing of connections

Neonatal period

moment of birth to day 28

Transitional events at birth

Baby need to start using its own lungs for gas exchange and the circulatory system has to start functioning as an adults

Factors that trigger transitional events

Blood flow from the umbilical cord stops - reducing pressure in heart

The lungs expand - blood flows to lungs

Cardiovascular transitional changes

Change in pressure in teh atriium and lung results in the flowing changes

Closing of ductus venous, foramen ovale and ductus aterious

Blood flow sthrough lungs and fills left atrium

left venticle has to work harder

respiratory transition chnages

Fluid clearance, changes to vascular flow, surfactant secretion, alveolar distention and establishment of breathing is needed

How does baby take first breath

Normal labour compresses the cord and lead to increased fetal CO2 and reduced oxygen - exaggerated once cord is cut

Shift stimulating change in teh respiratory centres of the brain to cause the first breath

Fluid drainage from lungs

ENAC - helps reabsorb lots of fluid from the lungs, starting a few days before natural delivery

During birth - chest wall of baby is compressed which helps clear remaining fluid

After birth - lymphatics and vacsular drainage, breathing removes some

Delayed cord clampung

More gas exchange

more iron and more fRBC

Respiratory distress syndrome

caused by insufficent surfactant in lungs - causing alveoli to collapse

Treatment involved Respiratory report, maybe survanta

If babies need respiratory support by 36 weeks gestational equivalent - termed chronic lung disease or bronchopulmonary dysplasia

Hemogobin Fetal vs adult

Fetal hb - 2 alpha and 2 gamma chains

making it better at takeing up oxygen not giving up

Adult hb - 2 alpha and 2 beta chains

Easier fro fetal blood chells to take oxygen from adult blood cells

Transition from fetal to adult Hb and RBC

Lowered RBC formation until about 6 weeks after birth due to ris ein oxygen that decreased EPO

Slowly fetal hb is replaced - until about 3 months

Bilirubin formed

Jaundice

A condition characterized by yellowing of the skin and eyes due to high levels of bilirubin, often more common in preterm infants.

Immature liver - lower bilirubin clearance

the faster RBC turnover - more bilirubin builds up

Can cause brain damage

Vitamin K and the newboen

Newborn cannot make vitamin K, not passed through placenta

at risk of hemorrage

Digestive system changes

Baby not used to having food move through intestine and needs to adapt

Probiotics for GUT reduces risk

APGAR

Universally scored system for assessing a baby’s health right after birth

1 and 5 mins

7 or more is normal

Pulse oximetry screening

Pulse oximetry looks for hypoxemia - sign of Critical Congenital heart disease

In term babies

• O2 sats >95% - discharge

• O2 sats <90% - admit to neonatal unit

Guthrie screening test

NNST

blood obtained from a heel prick and applied to a paper card

DNA obtained from the white blood cells for assessment of serious genetic diseases

Cystic fibrosis, phenylketonuria, congenital hypothyroidism, galactosaemic, spinal muscular atrophy

Postnatal hypoglycemia

Too low blood sugar of baby

Fetus builds up glycogen stores close to term but can only last so long. when runout, baby may start ketogenesis and lactate formation until milk can provide energy

Neonatal Hypoglycemia risk factors

Most common reasons for babies to spend a short amount of time in the special care nursery

IUGR babies - little fat to form ketones

Babies of diabetic women - adapted to higher glucose needs

Traumatic births/ long labour/fetal distress

Early growth in first few weeks

may loose up to 10% of weight

Usually due to loss of extracellular fluid but also change in the way baby obtains nutrients

should regain birth weight by 2 weeks of age

Growth of baby on growth charts an dthe goal is not not deviate much from the birth weight

Failure to thrive

Weight below 3rd centile

or

Dropping two major percentile lines over time

Nutrients required for the newborn

6 week old baby weighing 40kg may require over 600mls of milk per day

size of stomach is small, feeding must be frequent

Reasons fro failure tothrive

Inadequate food intake

inability to properly utilise food - reduced digestion or aborption

accessible energy utilisation - hyperthyroidism, coming of oxygen

Loss of nutrients - reflux

Skeleton of the infant

Spinal colum contains 33 separate bones (9 fuse and form 2 bones - scrum/coccyx)

Two primary curvatures care C shape spine

Most bones are well ossified except for the epiphysis. long bone growth until puberty ends

Fonatenel may last up to 2 years

Cranium large compared to rest of the face

Lungs of infant

As skeletal growth the chest increases - lung growth occurs

alevolar growth

Brain of infant

Synapses forming with all new information exposed to all senses

most rapid synaptogensis happens aright around birth

every second hundreds of millions of synapse are formed

Brain development of infant

Newborn quickly learns to distinguish voices, sounds, people and facial expressions

prefer speech from the language of their parents

Risk factors for preterm birth

Age of mother

Ethnicity

Smoking

Stress

Late or no antental care

low socio-economic status

High or low BMI

previous PTB

genital tract infections

IVF - assisted reproduction

Multiple gestation

Chronic or acute medical donsitions

Most common cause of neonatal death

preterm birth

Corticosteroids for PTB

Risk of PTB 24-34 weeks

betamethasone injections x 2

ensure Fetal lung is more fully developed

Tocolytic drugs for PTB

Anti contraction medication - can delay preterm labour longe enough to provide corticosteriods

Neuroprotectant for PTB

Magnesium sulfate

reduces cerebral pulsy

less than 30 weeks

Consider if between 30-33+6 weeks - preelcmpsia

Loading dose 4g over 2-, 1g maintence

Acute complications of PTB

Respiratory distress syndrome - resp support, low surfactant

Gastrointestinal complications - cannot coordinate breathing, sucking and swallowing - tube feeding

Jaundice - immature liver

skin not developed - dehydration and temp loss

Cardiovascular - patent arteriosus, brady, hypotension, iron deficnecy

Chronic complications of preterm birth

25% of preterm babies are visually impaired

10% are hearing impaired

40% chronic lung disease

Unquantified riks of heart disease and diabetes

LBW

Less than 2500g

FGR or IUGR

clinical features of in utero growth retardation

because of a pathology

higher stillbirth risk

sevre - less than 3rd centile

Early less than 32 weeks

late - after 32 weeks

SGA

(below 10th centile)

could be constitutively small or growth restricted

How is fetal growth restriction monitored

Fundal height

USS should be considered if reason to suspect slowing growth need over 3 consecutive though

Still birth

Usually due to congenital defects, suboptimal care contributes, placental insufficiency, maternal illness, fetal hypoxia, oxidative stress

Miscarriage

fetal loss before the time it could survie outside th womb

before 20 weeks QLD

75% before 12 weeks

Checkpoints for continuing pregnancy

Embryo/fetus may be lost at such checkpoints

Types of miscarriage

Threatened - Bleeding occurs before 20 weeks, no pain, cervix closed, pregnancy continues

Inevitable - Cervix open, bleeding and pain

complete - pregnancy ended and both fetus and pregnancy tissue have been passed

incomplete- some but not all of preganancy tissue hase been passed - bleeidng or infection

Blighted ovum - embryo has not devloped, placenta and empty sac

Recurrent miscarriage

2-5% of women

2-3 ina row

Cause, genetic, hormonal, immunological incompatibility, environment

recurrent miscarriage and the immune system

HLA proteins regulate tolerance of the baby

HLA in the mother and father must be similar enough but not the same

can lead to Immune rejection of babay

Transient Tachypnea of Newborn (TTN)

A respiratory condition that can occur if fluid does not clear from the lungs after birth, potentially requiring respiratory support.

Congenital disorder

Birth defects - structural or functional anomalies that occur due to abnormal developmental processes

What causes a congenital disorder

Environmental factors - drugs, alcohol, infection, medications

Parental factors - age, blood pressure, glucose, hormone concentrations

Genetic factors - single gene defect, chromosomal abnormalities

Genetics

Many babies are exposed before a women realises she is pregnant or changes in behaviour

It atkes around6 weeks for women to recognise they are pregnant and the most sensitive period to teratogen are between weeks 3-8

Fetal alcohol syndrome

Caused by alcohol exposure

Includes facial anomalies, growth deficiency, cognitive an behavioural issues

FASD vs FAS

FAS is a specific condition wherase, FASD is a spectrum of disorders

Poor learning/concentration

soical and commuincation problems

anxiety and mood dysregulation

facial features

lwo birth weight

heart, kidney, metabolic consequences

Micronutrient deficences

Folate, iodine and selenium

Genetic causes of embryonic defects

Advanced maternal age increases the risk of genetic defects

Consanguinity - related parents

Single gene defects

chromosomal abnormalities

Aneupoldiey - disruption of normal chromosme number Trisomy extra, monsomy missing

Trisomy 21- down syndrome

13 and 18 make it to term but survive days -months

Turner syndrime-45 X

Klinefelter’s syndrome XXY

Hypospadias

Displaced urethral meatus opening in males

Congenital uterine anomaly

4% of population

Most comoal is septal uterus

Ventricular septal defect

Hole in thE heart

Oxygen rich and oxygen poor blood mix

Renal agenesis

When one or both kidneys fail to develop

reduced anmiotic fluid

lungs dont dvelop properly

UNilateral can live with

cleft lip and palate

Can sometimes be picked up prenatally

Many differnt variations - unilateral vs bilateral, complete vs incomplete, lip and cleft or just one

Specal bottles needed to feed until surgery

neural tube defects

Failure of normal neural tube closure

Spina bifida - incomplete closing of the caudal neural tube - incomplete lumbar spinal column

NIPT

DNA of fetal origina can be detected in the maternal blood

10 weeks

not medicare

First trimester screen

11-13

assess anatomical features of the fetus

Nuchal transcalency thickness

• Papp-a decreased in trisomy preg

• B-HCG

• increasing in Trisomy 21, decreased in others

• blood test

second trimester screen

18-20 weeks

picking u major phsyical abnormalities in the baby

Diagnostic

Amniocentesis after 15 weeks

chronic villi sampling before 14 weeks