Flashcards in Repro Session 9 Deck (103):
How is blood mixing between deoxygenated blood from the SVC and oxygenated from the IVC in the fetal heart prevented as it enters the right atrium?
by the crista dividens= directs oxygenated blood towards foramen ovale to pass in to LA, then LV, and out through aorta to supply head structures e.g. brain
why is there little blood flow from the lungs into the left atrium in the fetal heart?
very high resistance pulmonary circulation so moost blood entering pulmonary artery from RV travels through the ductus arteriosus into the aorta, bypassing the lungs
what 2 things is the pattern of fetal circulation dependent on?
pressure in RA being greater than LA so oxygenated blood can pass all way across foramen ovale into LA
pressure in PA being greater than that in aorta so that blood from the RV can bypass the lungs to flow into the aorta to supply the rest of the fetal body, and be returned to the placenta for oxygenation
how are the necessary pressures for the pattern of fetal circulation met?
by the high flow resistance of the lungs
via what blood vessels is deoxygenated blood from the fetus returned to the placenta?
how does blood travelling from the placenta to the fetus bypass the liver?
via the ductus venosus
oxygenated blood entering IVC from placenta, via umbilical vein, mixes with what blood before entry into RA, and why is this not a problem?
venous blood from lower body of fetus but lower body relatively small and not that active metabolically, so there isn't much loss of oxygenation
how does oxygenated blood from maternal circulation provide oxygen to fetal blood in the fetal circulation to supply the fetal brain?
maternal blood passes through the remodelled spiral arteries of the endometrium of the uterus, to enter the intervillous spaces of the placenta where O2 diffuses across the syncytium of the villus, into the fetal capillaries located in the core of the villus, to then travel via the umbilical vein into the fetal circulation, as the umbilical vein passes through the umbilical cord. This venous blood enters the IVC, bypassing the liver via the ductus venosus and enters the RA, where it can then pass across the foramen ovale, into the LA, LV then out through the aorta to supply the brain.
how is the fetus adapted to a degree of hypoxia?
different Hb- fetal has higher O2 affinity and carries more O2 at lower pO2
how is fetal blood oxygenated at the placenta?
returned to placenta via umbilical arteries, which then allow the deoxygenated blood to pass into the fetal capillaries at the core of the villus, where blood is then oxygenated by O2 diffusion across the syncytium from the maternal blood bathing the villus that has entered the intervillous spaces from branches of maternal spiral arteries
how does maternal changes allow fetus to have relatively normal pCO2?
progesterone stimulated hyperventilation to remove metabolic CO2 produced by fetus
how might a baby with respiratory distress syndrome appear and why?
bluish discolouration of tongue and lips- central cyanosis:
-Lack of surfactant means increased surface tension, so the lungs are harder to inflate and fill with air as reduced lung compliance.
-There will be many collapsed alveoli as smaller alveoli collapse into larger ones due to lack of surfactant meaning increased surface tension and hence pressure, especially in the smaller alveoli as they have a smaller radius so increased pressure, so many alveoli can't take part in GE, there is ventilation/perfusion mismatch, resulting in arterial hypoxia.
when does fetal insulin secretion commence?
why does fetal bilirubin pass across the mum?
as unconjugated as cannot be excreted by fetal gut
cause of polyhydramnios?
oesophageal atresia- so amniotic fluid unable to be swallowed by fetus
antenatal bartter syndrome- problem with ATL of loop of Henle so excess urine production
why might amniocentesis be used to assess amniotic fluid?
to assess presence of neural tube defects or Down's syndrome
how are amniotic fluid volumes assessed?
what may cause oligohydramnios?
poor/absent fetal renal function
pre-eclampsia- example of reduced placental function
based on NS development, why are low thyroid hormone levels at birth dangerous?
cretinism- poor neurological development of neonate as hormones requried for completion of myelination which does not occur until into post-natal period
T3 and T4 necessary also for hyperplasia of cortical neurones and development of processes of neurones in NS development
what do thyroid hormones mediate in fetus from wk 12?
bone, hair growth, and NS development
what promotes fetal corticosteroid prod?
how does dramatic decrease in pulmonary vascular resistance occur at birth?
baby takes its 1st breath due to combination of physical trauma and cold temps, opening the alveoli
how does taking 1st breath close ductus arteriosus?
smooth muscles in wall of DA sensitive to high pO2 contracts
what regulates closing of DV after birth via sphincter in vessel?
what is the fetal period?
stage of intra-uterine life from end of 8th week till term
how is intrauterine growth restriction suggested in height measurement?
lag of 4cm or more of the fundal height
characterisitcs of lungs that fetal survival depends on?
thin walled air sacs for GE
surfactant to lower surface tension and allow air sacs to expand
4 stages histologically of lung maturation influencing viability of premature infants?
pseudoglandular- not viable
canalicular- may be viable at end
how is fetal urinary function assessed clinically?
use ultrasound to look at bladder emptying in fetus, with urine emptying into amniotic fluid
sources of variability in measurement of symphysis-fundal height?
lie of fetus
number of fetus
volume of amniotic fluid
extent of engagement of head
factors impacting on fetal growth?
Maternal nutrition and health
Efficiency of placenta
Adequate utero-placental blood flow
Maternal parity (primaparous mothers have smaller babies than multiparous)
Maternal habits (smoking, drug abuse etc)
Also, race, maternal height, weight,
how can uteroplacental circulation be assessed?
doppler ultrasound scan
why is an US scan at 20 wks in pregnant mothers a good time?
At this stage of pregnancy the organ systems are developed and can be visualised and anomalies can be identified.
ii. If anomalies are seen, the pregnancy is still early enough for possible intervention or
termination if appropriate.
iii. The inherent error in these measurements increases with gestational age such that
as a dating tool ultrasound becomes less accurate as the pregnancy proceeds.
uses of US in obstetrics, other than 20 wk scan?
Determine presence or absence of intrauterine pregnancy (or ectopic pregnancy)
Determine gestational age and measure fetal growth (when compared against standard
e.g., abdominal circumference (AC)
Identify multiple pregnancies
Detect fetal anomalies (e.g., neural tube defects), placental anomalies (e.g., placenta praevia)
Measurement of amniotic fluid
(Identify maternal pelvic anomalies)
(Guide for needle in amniocentesis)
why use a transvaginal US in early pregnancy if expectant mother has had severeal pregancy losses before?
see fetal cardiac activity in uterus which is very reassuring
rules out ectopic pregnancy
what can raised alpha fetoprotein levels be indicative of in pregnancy?
open neural tube defect
why is folic acid used in pregnancy?
reduce risk of neural tube defects
what can be given to mums antenatally to reduce risk of RDS if at risk of pre-term delivery?
steroid therapy to promote surfactant production, with production starting at around 20 wks
why is the symphysis-fundal height used in pregnancy assessment?
The uterus becomes an abdominal organ at about 12 weeks so the fundus is now palpable.
The height from top of symphysis pubis to top of fundus (in cm) correlates with the number
of weeks of gestation
use of fetal abdominal circumference measurement?
Measurement of fetal waist (at level of the umbilical vein) provides assessment of growth of
fetal liver and amount of sub-cutaneous fat etc. Glycogen laid down in the fetal liver
accounts for much of this growth.
what is meconium and how is it formed?
Typically, meconium are the first stools of a newborn baby – green, dark and sticky and
composed of cellular debris, mucous and bile pigments. It is formed from the digestion
products of amniotic fluid (cells and protein) the fetus has swallowed. The presence of
meconium in the amniotic fluid is an indicator that the fetus has had an episode of distress
what is the pattern of growth in the fetus?
crown rump length increases rapidly in the pre-embryonic, embryonic and early fetal periods, but absolute growth in embry period is very small eventhough intense activity, except growth of placenta
growth and weight gain accelerate in fetal period
weight gain slow at first- not really anything in 1st 2 periods, then increases rapidly in mid- and late fetal periods
embryo- intense morphogenesis and differentiaition, little weight gain, placental growth most sign
early fetus- protein deposition
late fetus- adipose deposition
importance of adipose deposition in late fetus stage?
stores for after birth= metabolism and thermoregulation
how do body proportions of fetus change?
dramatic change during fetal period
9wks= head approx 1/2 of crown-rump length
thereafter, body length and lower limb growth accelerates
3 ways of assessing fetal well being in ante-natal assessment?
mother- fetal movements- could keep a record
regular measurements of uterine expansion- symphysis-fundal height- non-invasive, tape measure used
when is viability of fetus possible?
once lungs have entered terminal sac stage= so >24 wks, as this is when surfactant is being produced as differentiation of type II pneumocytes
how to treat mother if pre-term delivery is unavoidable e.g. due to pre-eclampsia- failed placentation- failure of cytotrophoblast cells to differentiate from epithelial to endothelial to line maternal spiral arterioles, so resultant utero-placental circul defect with vasoconstricition?
Glucocorticoid treatment (of the mother)- increases surfactant production in the fetus
what techniques are used to assess fetal development?
o Ultrasound Scan
o Doppler ultrasound
o Non-Stress Tests (NST)
Monitors hear-rate changes associated with fetal movement
o Biophysical profiles (BPP)
5 measured variables
o Fetal movements kick chart
3 reasons for babies having a low birth weight?
suffered growth restriction- assoc. nenonatal morbidity and mortality
contrast symmetrical and asymmetrical growth restrictions
o Symmetrical Growth Restriction
Growth restriction is generalised and proportional
o Asymmetrical Growth Restriction
Abdominal growth lags
Relative sparing of head growth
Tends to occur with deprivation of nutritional and oxygen supply to fetus- occurs in latter part of pregancy due to maternal, fetal or utero-placental factors
when is a fetus regarded as having a growth restriction?
if estimated weight is below the 10th percentile for their gestational age
Partial pressure of O2 in fetus
4 kPa, contrast to 13.3 in adult
Saturation of fetal Hb at 4kPa
Hb concentration in fetus
18 to 20 g/dl
Benefit to fetus of Hb without beta chains
Doesn't readily bind 2,3BPG so more readily binds oxygen from mother's blood as higher affinity
Why is it necessary for mother to hyperventilate in pregnancy to prevent resp acidosis in fetus?
Fetus unable to compensate for acidosis by increasing hCO3- in blood as no excretory function of fetal kidneys
Saturation of fetal blood reaching brain
60% as 70% in umbilical vein, then does to 65 due to mixing with lower body blood and then to 60 as small amount of pulmonary venous flow mixes with blood in LA
How can amount of surfactant in fetus be measured
In amniotic fluid as washed out into fluid by in utero breathing movements of fetus
What provides a good index in fetus of developing control systems?
Heart rate variability
what does amniotic fluid comprise?
cells from fetus and amnion, and a variety of proteins
functions of pre-embryonic period?
cell gowth in correct location in the body
functions of embryonic period?
grow systems of the body, organs develop
when is placenta at its term size?
end of 1st trimester, growth is mainly responsible for overall growth in embry period and weight gain
why is protein deposition important in early fetal period?
for muscle growth
why is US used early in pregnancy?
to calculate age
to rule out ectopic pregnancies
to look at number of fetuses
what do non-stress tests measure?
HR changes associ with fetal movement
5 variables measured in biophysical profiles using ECG and USS to assess fetal growth and development?
fetal amniotic fluid volume
when might a multiparous women experience fetal kicking movments in comparison to a primaparous women?
earlier on in pregnancy
what should the symphysis-fundal height be at 28 weeks?
24cm or less would indicate an intrauterine growth restriction/fetal growth restriction
systems assessed when measuring fetal movement in biophysical profiles?
systems assessed when measuring fetal tone in biophysical profiles?
systems assessed when measuring fetal amniotic fluid vol in biophysical profiles?
systems assessed when measuring fetal HR in biophysical profiles? (NON STRESS TEST)
systems assessed when measuring fetal breathing movments in biophysical profiles?
what factors may cause a reduction in scores achieved when measuring biophysical profiles in fetus?
fetal sleep cycles
maternal dehydration or hunger
maternal sedation and fetal alcohol syndrome
fetal compromise due to hypoxaemia
why might a fetus be classified as at-risk near to term?
maternal heart or liver disease
fetal growth retardation
what is the expected relationship between fetal movements and heart rate in non-stress tests?
3 or more fetal movements should be accompanied by an increase in fetal HR
how can you decide on lie and presentation of fetus in early labour apart from USS?
advantages of a scalp electrode in monitoring fetal HR?
allows continuous close monitoring regardless of maternal position
what does gestational age refer to?
the duration of the pregnancy dated from the 1st day of the LMP which precedes ovulation and fertilisation by around 2 wks
what name is given to the adherence of the blastocyst to the endometrium following ZP disappearance?
when is crown rump length measured to date the pregnancy and estimate estimated delivery date?
between 7 and 13 wks= 1st trimester scan
why is scan done in 1st trimester?
early fetal cardiac activity- is pregnancy viable
check location- ectopic?
number of fetuses
what is biparietal diameter and when is it used?
date pregnancies in 2nd and 3rd trimesters as CRL becomes less accurate
distance between parietal bones of fetal skull
used with fetal abdom circumference and femur length
why might a 3D or 4D USS be used?
good at looking at morphology e.g. cleft lip, so useful compimentary tool to standard 2D USS
may contribute to bonding before birth
what fetal emergency may occur when delivering a macrosomic baby?
shoulder dystocia: the anterior shoulder of the infant cannot pass below, or requires significant manipulation to pass below, the pubic symphysis. It is diagnosed when the shoulders fail to deliver shortly after the fetal head. Fetal demise can occur if the infant is not delivered, due to compression of the umbilical cord within the birth canal
importance of antenatal screening for babies with a low birth weight?
can identify those which have suffered growth restriction
what may cause an intrauterine growth restriction?
maternal smoking and alcohol drinking
what part of resp system produced in embryonic period?
bronchopulmonary tree, so just airways
tissue for gas exchange not grown until well into fetal period
where does respiratory diverticulum arise?
at beginning of foregut
how is gut tube separated from resp diverticulum?
by tracheoesophageal septum
during what stage do bronchioles start to develop from bronchi with duct system beginning to form?
during what stage does budding from bronchioles take place forming resp bronchioles?
when do terminal sacs start to bud from resp bronchioles?
wk 26 to term in terminal sac stage
type I and II pneumocytes differentiate now too
how is normal lung development driven by amniotic fluid moved into the lungs?
factors exchanged between amniotic fluid and lungs and these drive development during terminal sac stage
2 reasons why amniotic fluid moved into lungs during development?
breathing movements allow conditioning of resp musculature so muscles ready to take over breathing at birth
factors in fluid are crucial for normal lung development
2 lung charactersitics necessary for fetus viability?
thin walled air sacs for GE
when is the definitive HR achieved and why is this important to know?
fetal bradycardia assoc with fetal demise, so fetal HR assessed with antenatal assessment
why is fetal kidney function NOT necessary for survival in utero?
all waste products of fetus excreted by maternal kidneys via exchange across placenta
BUT poor kidney function causes oligohydramnios
when do corticospinal tracts appear?
form in 4th mnth, required for coordinated voluntary movements
why are infants very immobile at birth?
corticospinal tract myelination incomplete, begins only in 9mnth and is finished postnatally
what is quickening?
mother becomes aware of fetal movements from wk 17 onwards