Flashcards in Repro Session 9 Deck (152):
What is the organogenetic period of human development?
Describe growth in the embryonic period.
Foetal growth is very small but placental growth is large
Broadly describe the foetal period.
Growth and physiological maturation of structures established in the embryonic period
When is the embryonic period?
3-9 weeks after fertilisation
When is the foetal period?
9-38 weeks post fertilisation
Why is human pregnancy considered to be 40 weeks when human gestation is 38 weeks?
Can be +/- 2 weeks due to natural variation but this is masked by using the date of the LMP to calculate pregnancy weeks
Why is using LMP to date pregnancy prone to inaccuracy?
Irregularity of menstrual cycles and confusion with implantation bleeding
During which periods does CRL increase rapidly?
Pre-embryonic, embryonic and early foetal
When is increase in CRL most striking?
Describe how the body proportions of the foetus changes during development.
At 9 weeks head = 0.5 CRL, reducing to 0.3 around 20 weeks and reaching 0.25 at term
What happens after week 9 that allows the body proportions of the foetus to near those seen in the adult?
Acceleration of body and lower limb growth
What CRL would be expected at 9 weeks?
What CRL would be expected at 9, 12, 16 and 38 weeks respectively?
5, 8.5, 16 and 36 cm
Around what time does the face become more distinguished and the limbs reach their relative lengths?
Briefly describe the 16 week old foetus.
Weighs less than 500 g and is covered in lanugo with head and eyebrow hair visible
When does weight gain increase rapidly in utero?
2nd half of intrauterine life, especially during mid- and later foetal periods
When is 50% of full term weight added to the foetus?
Mid and late foetal periods
What deposition dominates in weight gain of the early foetus?
Does protein deposition always dominate in weight gain of the foetus?
No, adipose deposition takes over in late foetal stages
Why might a pre-term baby be unable to maintain a constant body temperature?
Lack of brown adipose tissue for thermoregulation due
What are non-pathological causes of low birth weight?
Prematurity or constitutionally small
How is a SFD differentiated from IUGR?
By doppler- abnormal in IUGR
What happens if a foetus is SFD and has an abnormal Doppler scan at >36 weeks?
Labour is induced or C-section performed
How is IUGR identified preterm managed?
Why is obstetric USS performed in early pregnancy?
Confirm gestation, pregnancy site, number of foetuses, age and rule out ectopics
When is USS in early pregnancy usually performed?
What allows a more accurate ageing of a foetus than calculation of pregnancy from LMP?
CRL between weeks 7-13
What method can be used for early obstetric USS if there are concerns?
When is obstetric USS routinely performed?
What is the 20-week obstetric USS also known as?
Why is an obstetric USS performed at 20 weeks?
To assess foetal growth and identify congenital malformations as all are detectable at this stage
How does a 4D USS scan differ from a 3D scan?
Includes time dimension, gives better resolution image
What measurements of the foetus are used in pregnancy?
Biparietal diameter, abdominal circumference, femur length, foot length
Why are biparietal diameter, abdominal circumference and femur length used together when assessing foetal growth?
Used for dating and to identify asymmetrical growth restriction
What does asymmetrical growth restriction usually spare?
What is symphysis-fundal height?
Measurement made with tape measure between maternal public symphysis and uterine fundus to assess uterine expansion out of the pelvis
What is the average birth weight?
What birth weight is suggestive of a growth restriction?
Less than 2500 g
What birth weight is determined as macrosomia?
What does macrosomia indicate in the mother?
What development of the respiratory system takes place in the embryonic period?
Bronchopulmonary tree from diverticulum that appears at week 4
How many generations of subdivisions are made in the bronchopulmonary tree by the end of the 6th month of development.
How many bronchopulmonary divisions arise postnatally?
When is the pseudo glandular stage of respiratory system development?
What happens in the pseudo glandular stage of respiratory development?
Duct systems begin to form within bronchopulmonary segments to create bronchioles
What epithelium lines the bronchioles and their buds during the pseudo glandular stage?
When is the canalicular stage of respiratory development?
What happens in the canalicular stage of respiratory development?
Budding from bronchioles to form respiratory bronchioles
When is the terminal sac stage of respiratory development?
What happens in the terminal sac stage of respiratory development?
3-6 alveolar ducts from each respiratory bronchiole end in terminal sacs that bud from the bronchioles, surrounded by flat alveolar cells in close contact with capillaries
When are there enough respiratory components to guarantee adequate gas exchange if delivery takes place?
End of the 7th month
What happens to type I pneumocytes lining terminal sacs during the last 2 months of development?
Become thinner so surrounding capillaries protrude to create the blood-air barrier
Are mature alveoli present before birth?
When do type II pneumocytes develop?
What molecule is surfactant rich in?
What is the composition of the fluid filling the lungs in T2 and T3?
High [Cl-], small amount of protein, mucus from bronchial glands and surfactant
What is the action of the significant increase in surfactant production in the last 2 weeks on the lungs?
Activates alveolar macrophages
What is the purpose of foetal breathing movements?
Condition respiratory musculature and draw in amniotic fluid
What is neonatal respiratory distress syndrome?
Insufficient surfactant production --> high blood-air surface tension --> alveoli collapse on expiration
What do partially collapsed alveoli in neonatal respiratory distress syndrome contain?
Fluid high in protein, hyaline membranes and lamellar bodies
How is neonatal respiratory distress syndrome managed if pre-term delivery is unavoidable?
Give glucocorticoids to mother to increase foetal surfactant production and administer synthetic surfactant to neotnate
What is the foetal circulation arranged to ensure?
Oxygenated blood of ~80% sats from umbilical vein is circulated around foetus and retuned via umbilical artery at ~58%
What range should foetal HR lie within from ~15 weeks onwards?
What are the three shunts present in the foetal CVS?
Ductus venosus, foramen ovale, ductus arteriosus
What guides flow of blood through foramen ovale?
Valve of IVC
What guides a small amount of bloodflow from the RA to RV to allow for lung development?
Where does ductus arteriosus shunt blood from and to?
From PT to aorta
When does foetal kidney function begin?
What is the result of renal agenesis in utero?
What are the possible consequences of oligohydramnios?
Club foot, lung hypoplasia
Is foetal kidney function necessary for survival in utero?
What is hydramnios?
Excess amniotic fluid
What are the primary causes of hydramnios?
Idiopathic, maternal diabetes, CNS deformity, GI defects (prevented swallowing of neural/musclar cause)
What is the first system to start and last system to finish developing in utero?
What are corticospinal tracts required for?
Coordinated voluntary movements
When do coordinated voluntary movements of the foetus begin?
What is 'quickening'?
Patterns of foetal movement that are detectable by the mother
When does quickening usually arise?
17 weeks onwards
What does the start of quickening depend on?
Number of previous pregnancies, size of baby, size of mother
Can foetal movements be identified before 8 weeks?
Why do breathing and suckling movements start in the 4th month of development?
To 'practise' for postnatal life
Why are humans neurologically immature at birth?
Due to implications on head size and vaginal delivery
When does myelination of the brain start?
What evidence of postnatal brain myelination is there in the neonate?
Increasing infant mobility in the 1st year
What determines viability of a pre-term baby?
Development of the respiratory and CNS
When does myelination start in the spinal cord?
When do the gyri and sulci arise?
What causes development of the gyri and sulci?
Cerebellar hemispheres grown larger than the skull
What respiratory event occurs at the same time as the onset of myelination in the brain?
Increased surfactant production
What forms the maternal arm of the materno-foetal exchange system at the placenta?
Uterine arteries and veins emptying into intervillous spaces
What forms the foetal arm of the materno-foetal exchange system at the placenta?
Umbilical arteries branching into foetal capillaries in the chorionic villi and umbilical vein
How does foetal pO2 compare to the maternal value?
Foetal = 4 kPa, maternal = 11-13 kPa
What allows the foetal oxygen content to be sufficient at the partial pressure seen in utero?
Foetal haemoglobin variant, foetal Hb levels > adult male levels, increased maternal 2,3-DPG levels, foetal haematocrit levels > adult levels
Does the foetal haemoglobin variant bind as effectively as the adult variant to 2,3 DPG?
How do hormones in the mother contribute to the concentration gradient between the maternal and foetal circulations?
Progesterone causes hyperventilation creating a physiological respiratory alkalosis that results in lowered maternal pCO2
Describe the Bohr effect in the mother that aids gas exchange at the placenta.
CO2 moves into intervillous blood causing reduced pH and lowering the affinity of Hb for O2
Describe the Bohr effect seen in the foetus that aids gas exchange at the placenta.
Foetal CO2 is lost causing an increased pH resulting in an increased affinity of Hb for oxygen
What is the difference between the double Bohr and Haldane effects?
Bohr-determined by pCO2, Haldane-determined by [O2]
Describe the double Haldane effect.
In the maternal blood Hb releases O2 and therefore accepts more CO2 whilst in the foetus more CO2 is released so it can accept more O2
What prevents local alterations of pCO2 in the materno-foetal circulation?
Double Haldane effect
Where does the ductus venosus connect?
Umbilical vein to IVC
What is the purpose of the ductus venosus?
Cause blood entry to the RA bypassing the liver so that sats only drop by 5%
Why is the liver hugely metabolically active in utero?
Synthesising haematological and immunological proteins
Does the foetal liver have hepatobiliary function?
What regulates the small amount of blood entry into the liver sinusoids in utero?
Sphincter within ductus venosus
What prevents heart overload in the foetus during uterine contractions?
Closure of the sphincter in ductus venosus
Why might physiological jaundice be seen at birth?
Foetal liver does not have hepatobiliary function so cannot conjugate bilirubin
What forces the 2-leaved foramen ovale apart?
p(RA) > p(LA)
What forms the crista dividens?
Free border of septum secundum
What effect does the crista dividens have on bloodflow?
Divides into 2 streams
Where does the minor steam of blood from the crista dividens flow?
To the RV to mix with deoxygenated blood from the SVC
What causes the sats of blood in the LA to be around 60%?
Small amount of pulmonary venous return
What shunts blood from the PT into the aorta?
Why is blood shunted from the PT into the aorta distal to the supply to the head and heart?
Allows pulmonary circulation to develop without significantly reducing oxygen sats
When are transient episodes of hypoxia seen in utero?
During labour when uterine contractions compress the umbilical vein
What happens to bloodflow in the foetus during transient episodes of hypoxia?
Redistributed from GI tract, kidneys and limbs to the heart and brain
What are the effects of foetal chemoceptors detecting low pO2?
Vagal stimulation resulting in bradycardia
Why does foetal vagal stimulation result in bradycardia?
To reduce oxygen demands
What can chronic hypoxaemia lead to in the foetus?
Growth restriction and behavioural changes
What causes behavioural changes due to chronic hypoxaemia in the foetus?
REM sleep pattern disruption
What are the necessary hormone for foetal growth?
Insulin, human placental lactogen, leptin, IGFI, IGFII, EGF, TGF-alpha
What type of cellular growth is seen at 0-20 weeks?
What type of cellular growth is seen at 20-28 weeks?
Hyperplasia and hypertrophy
What type of cellular growth is seen at 28 weeks to term?
What type of growth restriction is seen at 0-20 weeks?
What type of growth restriction is seen at 28 weeks to term?
Where is foetal leptin produced?
What do mutations to IGFI gene result in?
IUGR and growth retardation after birth
Which growth hormone dominated in T2 and T3?
What effects does IGFI have?
Mitogenic and anabolic
Is IGFI or II nutrient-independent?
What is the benefit of IGFII dominating foetal growth in T1?
Nutrient independent so is not affected by maternal nutritional status that may be poor due to nausea and vomiting
What is Barker's hypothesis?
Nutritional and hormonal status during foetal life can influence adult health
What does Barker's hypothesis suggest IUGR leads to?
Obesity, hypertension, hyoercholestrolaemia, CVD, T2DM
What is the purpose of amniotic fluid?
Allow for foetal movements, prevent adherence of embryo to amnion and protection from jolts
Where is amniotic fluid derived in early pregnancy?
In part by amniotic cells but primarily from maternal blood
When does the foetus begin to swallow amniotic fluid?
Beginning of the 5th month
When does the foetal kidney start to contribute towards amniotic fluid volume?
What foetal system other than the urinary system contributes to amniotic fluid volume?
How does the volume of amniotic fluid progress through pregnancy?
10 ml @ 8 weeks, 1l @ 38 weeks, reduces post-EDD
Why does amniotic fluid volume decrease post-EDD?
Senescence of placenta
What volume can the foetal kidneys contribute to the amniotic fluid in T3?
Up to 800 ml
What is the composition of amniotic fluid?
98% water, electrolytes, creatinine, urea, bile pigments, renin, glucose, hormones, foetal cells, lanugo, vernix caseosa
What is vernix caseosa?
Covering of skin from foetal surfactant that water-proofs the skin
What forms meconium?
Bile and intestinal secretions, creatinine, urea, rening glucose, hormones, foetal cells, lanugo and vernix caseosa
What is meconium?
First stool passed by the neonate
When may meconium leak into the amniotic cavity?
How does amniotic fluid enter the foetus?
Intramembranous across placenta and foetal membranes, through lungs and by swallowing
How does amniotic fluid exit the foetus?
As urine, from the lungs and head
How does amniotic fluid move out of the amniotic cavity?
Describe the process of amniocentesis.
Fine-gauge needle under US guidance to remove amniotic fluid at 15 weeks