Preparation for birth & delivery Flashcards
how do we assess interuterine growth?
post birth - birth weigh is a good proxy
before - its difficult
Maternal weight gain, uterine fundal height and maternal abdominal girth are still used in resource-poor situations but have a low predictive value for complications of pregnancy.
Ultrasound provides more accurate estimates, and biparietal diameter, crown-rump length, femur length and abdominal diameter are routinely measured.
how do we date pregnancies?
why is it important?
Obstetricians date a pregnancy from the first day of the last menstrual period (LMP), as this is usually known, unlike the date of ovulation. Pregnancy or gestational dates are therefore 14 days in advance of the dates post-fertilization or post-conception used by embryologists.
used to monitor growth rate - important§
is absolute birth weight a good parameter?
list some better ones
low birthweight being defined as <2.5kg and high birthweight or macrosomia being >4kg.
but this depends on many factors
Now use centile charts, with small for gestational age (SGA) being below the 10th centile, and large for gestational age (LGA) above the 90th centile
take into account ethniciity, BMI, and other factors
Fetuses that are growth restricted due to lack of oxygen or nutrients usually show what signs
Fetuses that are growth restricted due to lack of oxygen or nutrients usually show brain-sparing,
in that blood is directed to the brain at the expense of peripheral tissues.
Hence, head circumference continues to enlarge, whereas abdominal circumference reflecting development of the liver lags behind.
what is meant by asymmetric growth,
Hence, head circumference continues to enlarge, whereas abdominal circumference reflecting development of the liver lags behind.
This is referred to as asymmetric growth, and the increase in blood flow to the brain can be detected by Doppler ultrasound assessment of middle cerebral artery flow.
give some maternal factors which affect fetal growth?
- Uterine size.
- nutrition
- Parity
- socio-economic background + other environment factors
- Diseases
- envirionmental factors
describe how the uterine size of the mother can affect fetal growth
big uterus = more growth
this is still observed after birth.
eg - shire and shetland ponies.
Human fetuses in multiple pregnancies tend to show growth retardation when total fetal weight is about 3.2kg, which occurs at week 30 with twins and week 26 with quads.
describe how nutrition can affect a fetus growth
worldwide maternal undernutrition is the commonest cause of fetal growth restriction (FGR).
in developed world - its normally resttricted blood to placenta that causes FGR.
In the developed world, more and more women enter into pregnancy obese due to increased intake of a ‘Western- style’ diet that is high in sugar and fat. Maternal obesity and obesogenic diets also have impacts on fetal growth and pregnancy outcome, with those women at greater risk of preeclampsia and gestational diabetes and delivering FGR and large for gestational age/macrosomic babies.
describe how Parity can affect baby growth
On average, first babies are smaller than subsequent babies.
Expansion of the uterus and remodelling of the maternal vessels together with the maternal physiological adaptations occurs more readily in subsequent pregnancies.
describe how Socio-economic and other environmental factors can impact fetal growth
Low birthweight is correlated with low socio-economic status of the mother
may ge generational
Smoking and drug abuse reduce fetal growth by up to 300g in a dose-dependent fashion.
Similarly, teenage mothers give birth to smaller babies because they often are still growing themselves and apportion available nutrients less readily to the fetus.
describe how Diseases can affect fetal growth
Maternal cardiovascular diseases, such as hypertension, reduce birth weight, possibly due to reduced maternal blood flow in the placental intervillous space.
In contrast, poorly controlled diabetes leads to increased birth weight due to fetal hyperglycaemia and hyperinsulinaemia.
effect of hypertension on birthweight?
hypertension, reduce birth weight, possibly due to reduced maternal blood flow in the placental intervillous space.
effect of poorly controlled diabetes on bith weight?
In contrast, poorly controlled diabetes leads to increased birth weight due to fetal hyperglycaemia and hyperinsulinaemia.
Environmental factors - how they affect fetal growth
The hypobaric hypoxia associated with pregnancy at high altitude is associated with a reduction in birthweight of 100g per 1,000m of ascent.
Indigenous populations are relatively protected due to adaptive mutations that increase blood flow to the uterus.
_____ ______ is the major cause of FGR in developed countries.
Placental insufficiency is the major cause of FGR in developed countries.
placental insufficiency is commonly associated with?
commonly associated with deficient remodelling of the maternal spiral arteries, leading to malperfusion of the placenta.
how can we clinically assess the placental function
assessed clinically by Doppler ultrasound assessment of the waveform in the uterine artery at the point where it crosses the internal iliac artery (standardized location). High resistance is associated with FGR and pre-eclampsia.
(might look for reduced diastolic flow - showing poor spiral artery remoddeling)
problems with malperfusion of the placenta?
Malperfusion causes infarction of the placenta and loss of surface area for exchange.
T or f
Severe placental pathology affects the waveform in the umbilical arteries
T
High placental resistance, as indicated by ………………whihc facotrs? ……… is associated with which conditions?
High placental resistance, as indicated by
- absent or reversed end-diastolic flow
is associated with
- FGR,
- fetal hypoxaemia
- and impending stillbirth
Compromise of barrier function may lead to what for the fetus/
Compromise of barrier function may lead to excessive levels of maternal cortisol or xenobiotics crossing the placenta, and influencing fetal growth.
The drive to fetal growth is provided primarily by ….
The drive to fetal growth is provided primarily by the genes the fetus inherits.
give 4 fetal factors influencing growth
- fetal sex
- fetal genome
- infection
- Endocrine factors
describe how fetal sex can influence fetal growth
In all ethnic groups, male neonates are significantly heavier, longer and have a larger head circumference than females.
describe how the fetal genome can influence fetal growth
Specific gene defects also alter intrauterine growth, but account for <10% of cases of FGR.
describe how fetal infection can affect fetal growth
Toxoplasmosis, rubella, cytomegalovirus, and herpes (TORCH) can all cause FGR.
As they usually occur in the first trimester they cause symmetric growth reduction, and account for <10% of cases.
describ how fetal derived endocrine factors can affect fetal growth
Maternal hormones such as insulin and TSH do not cross the placenta, and fetal growth is driven by its own endocrine environment.
The IGF family, IGF-I and IGF-II, is a powerful regulator of fetal growth, as evidenced by disorders of imprinting.
Fetal insulin may be important in late pregnancy, and high levels are associated with increased glucose uptake and body weight.
describe the role fetal IGF plays in fetal growth
The IGF family, IGF-I and IGF-II, is a powerful regulator of fetal growth, as evidenced by disorders of imprinting.
IGF-II is normally only expressed from the paternal allele, but uniparental disomy or loss of imprinting control can lead to a double dose of IGF and the hypertrophic Beckwith- Wiedemann syndrome.
Levels of IGF-I in the fetus are responsive to oxygen and nutrient availability, and correlate with birthweight.
IGF activity is regulated by gene expression and also through the family of IGF-binding proteins.
describe Beckwith- Wiedemann syndrome.
IGF-II is normally only expressed from the paternal allele, but uniparental disomy or loss of imprinting control can lead to a double dose of IGF and the hypertrophic Beckwith- Wiedemann syndrome.
Levels of IGF-I in the fetus are responsive to oxygen and nutrient availability, and correlate with ________
Levels of IGF-I in the fetus are responsive to oxygen and nutrient availability, and correlate with birthweight.
Both SGA and LGA babies are at risk of increased neonatal morbidity and mortality; why?
Both SGA and LGA babies are at risk of increased neonatal morbidity and mortality;
SGA: because of poor organ development and compromised nutritional reserves,
LGA: because of difficulties in passing through the birth canal (obstructed labour).
T or f?
Longer term, adults that were born growth restricted are at increased risk of chronic diseases, such as cardiovascular disease, type 2 diabetes, obesity and some cancers.
T
shows that intrauterine growth can affect adult life for years to come
6 ways fetal circulation differs from adult?
- supplies the placenta
- mainly bypasses lungs
- 2 shunts: foramen ovale and ductus arteriosus for pulmonary bypass
- Right ventricular output is higher than left due to the shunts.
- Total cardiac output (both ventricles) is about 4 fold higher than in the adult.
- Oxygenated blood coming from the placenta by-passes the liver by the ductus venosus
(DA)
____% of the combined fetal cardiac output goes to the placenta which has a low resistance.
40-50% of the combined cardiac output goes to the placenta which has a low resistance.
Total peripheral resistance and blood
pressure are ______ in fetuses than adults.
Total peripheral resistance and blood
pressure are lower in fetuses than adults.
Pulmonary vascular resistance is _____ in utero.
Pulmonary vascular resistance is high in utero.
the foramen ovale does what?
shunts blood from the right atrium to the left atrium
the ductus arteriosus does what?
shunts blood form pumlmonary atery to the aorta
the ductus venosus does what?
allows the umbilical vein to bypass the liver
fetal or adult?
the heart chambers beat in parallel
fetus
how does the fetus ensure the brain gets most of the oxygen delivered?
Preferential streaming of flow from the DA in the inferior vena cava to the FO ensures blood with the highest saturation is delivered to the brain
Only after this point, will the blood mix with blood from the right ventricle through the pulmonary artery and the DA to supply the rest of the body
does the ductus arteriosus enter the aorta after the Brachiocephalic artery has branched?
yes
how is fetal haemoglobin asapted for its purpose?
fetal Hb has a reduced affinity for 2,3DPG, which increases O2 binding.
The concentration of 2,3DPG is also lower in fetal than maternal erythrocytes.
Oxygen uptake across the placenta is facilitated by the double Bohr shift which helps to maintain the diffusion gradient across the placenta but the most important thing about the increased affinity is the higher oxygen content of blood at a relatively low pO2.
this is importnat:
most important thing about the increased affinity is the higher oxygen content of blood at a relatively low pO2.
Yes
describe the fetal double bohr effect
when does fetal alveolar developement occur?
Alveolar development only occurs in the last few weeks of gestation, and continues after birth.
The respiratory epithelium differentiates into which types of cells?
The respiratory epithelium differentiates into type I and type II pneumocytes.
which pneumocytes secrete surfactant?
Type 2
effect of surfactant?
reduces surface tension effects.
problems in the lungs of premature babies?
how can it be treeated?
Hence, premature babies suffer severe respiratory distress.
An artificial surfactant is now available that can be introduced into the bronchi, but can also give the mother a high dose of synthetic glucocorticoids 24 hrs before having to do a premature delivery in order to stimulate lung maturation.
The influence of cortisol on surfactant production is shown in sheep models where cortisol treatment in one twin increases surfactant production
Fetal breathing movements can be detected from around ____ weeks of gestation
Fetal breathing movements can be detected from around 10 weeks of gestation
describe mechanostimulation for lung developement
al breathing movements can be detected from around 10 weeks of gestation, and provide important mechano-stimulation for alveolar development and surfactant release.
Babies with congenital diaphragmatic hernia suffer from…..
Babies with congenital diaphragmatic hernia suffer from hypoplastic lungs.
Attempts have been made to rectify the defect in utero to preserve lung development.
where does the amniotic fluid come from?
The lungs secrete fluid which contributes to the overall amniotic fluid volume,
but the main contributor comes from the kidneys – a hypotonic urine as the Loops of Henle are not well developed.
There is also fetal swallowing of amniotic fluid, and so a constant turnover.
what is oligohydramnios.
Fetal stress is associated with reduced fluid volumes – oligohydramnios.
In all species studied to date, there is an increase in ___________ concentration in the fetal circulation towards term
In all species studied to date, there is an increase in glucocorticoid concentration in the fetal circulation towards term
increasing fetal cortisol has what effect on the fetus
This increase in cortisol is responsible for maturing many tissues in preparation for extrauterine life, such as stimulating gluconeogenesis in the fetal liver.
It also causes concomitant changes in the fetal concentrations of other hormones,
e.g. tri-iodothyronine and adrenaline, which also contribute to maturation or functional activation of key tissues essential for neonatal survival.
describe fetal cortisols effects on the gut
- acid secretions
- digestive enxymes
- mucosal turnover
describe fetal cortisol effecs on adipose tissue
leptin production
UCP expression
describe fetal cortisol effects on the kidney
- GFR
- tubular sodium reabsorbtion
- deiodinase activity
- GR and MR receptors
- renin-angiotensin II system
describe fetal cortisol effecs on hte lugn
surfactant production
alveolar density and wall thickness
elastin and collagen expression
ebta-adrenergic receptors
ACE enzyme activity
effect of fetal cortiso on the liver?
glycogen and gluconeogenesis enzyme
IGF gene expression
beta adrenergic and GH angiotensin II receptros
what hormonal changes lead to initiation of partiuition?
involve changes in cortisol, oestrogen and prostaglandin and oxytocin concentrations as seen in other species,
although there is little evidence for a prepartum decline in the maternal progesterone concentration in women
image for initation of partuition in women:
believed process of partiution:
(LONG)
- activation of feta ladrenal gland = more fetal cortisol and dehydroepiandrosterone sulphate, DHEAS.
- cortisol = maturity of key fetal tissues
- increased DHEAS production results in a rapid rise in maternal oestrogen levels close to term
- rise in oestrogen availability in the human uteroplacental tissues (amnion, chorion, decidua and myometrium) leads to cervical ripening and increased uterine contractility via enhanced PG synthesis
5.
T or F
Cervical softening and ripening is essential for delivery to occur.
T
in women - can removing the progesterone block myometrial contraction?
no
In women, there is no evidence of removal of the progesterone block to myometrial contraction, although there may be regional changes in the oestrogen to progesterone ratio and in expression of the different progesterone receptor isoforms, which may affect contractility in different regions of the uterus by local variations in PG synthesis and metabolism.
what does CRH do?
corticotrophic releasing hormone:
CRH is detectable in fetal and maternal plasma and rises in concentration towards term and in labour.
what dfoes CRH act on?
CRH acts on
(i) the fetal adrenal to increase DHEAS production directly and indirectly via the fetal pitiutary
(ii) the uteroplacental tissues to increase PG availability and
(iii) the myometrium to inhibit contractions via increasing cAMP
In culture, trophoblast CRH production is inhibited by _________ and stimulated by _________ & ____
In culture, trophoblast CRH production is inhibited by progesterone and stimulated by catecholamines and glucocorticoids
how does fetal growth cause myometrial activation
stretch of the human uterus with fetal growth appears to have an important role in increasing GAP junction proteins and, hence, in causing myometrial activation
statement L
Initiation and progression of human labour, therefore, involves a combination of fetal, local, mechanical and maternal factors
Initiation and progression of human labour, therefore, involves a combination of fetal, local, mechanical and maternal factors
describe the mechanism of myometrial contraction
(7)
- rising oestrogen increases contractile protein expression (actin and myosin)
- Contraction of the filaments requires ATP generated by myosin light chain kinase
- MLCK is activated by the calcium binding protein, calmodulin (CAM) which, in turn, is activated by Ca2+ ions.
- During contractions, [Ca++]i increases by increase of Ca++ influx through Ca++ channels and by release of Ca++ stored in the sacroplasmic reticulum.
- Uterotonins increase Ca2+i
- agents that reduce myometrial activity act by inhibiting Ca++ release from the intracellular stores or by reducing MLCK activity. These inhibitory activities are often mediated via cAMP or cGMP
- Contraction of the myocytes is coordinated by cell to cell coupling effected by formation of intercellular GAP junctions between adjacent myocytes. These GAP junctions depend on connexin proteins, expression of which is influenced by steroids and mechanical stretch on the uterus. Connexin abundance and the number of GAP junctions increase with the onset of labour.
Agents that increase cAMP or cGMP, therefore, ______ uterine contractility (tocolytics).
Agents that increase cAMP or cGMP, therefore, decrease uterine contractility (tocolytics).
These GAP junctions depend on connexin proteins, expression of which is influenced by ……
(myometrial muuscle developemnnt)
These GAP junctions depend on connexin proteins, expression of which is influenced by steroids and mechanical stretch on the uterus.
image
Labour is preceded by…
Labour is preceded by Braxton-Hicks contractions
how many stages does labour have?
3
describe the first stage of labour
Stage 1: Increasing uterine activity and cervical dilation.
The ‘show’ of blood and mucus occurs at this stage.
Cervix dilates to 10cm.
Regular contractions force the babies’ head down into the birth canal, encouraging dilation and evoking neuroendocrine reflexes that produce the positive feedback element to labour.
Lasts 10- 12h in primagravida (first pregnancy) and 6-8h in multigravida.
Mild maternal hyperventilation.
describe stage 2 of labour
Stage 2: Expulsion of fetus.
This stage involves voluntary effort as well as uterine contractions.
The baby also needs to engage, flex and rotate.
Lasts 45-120min in primagravida and 15-45min in multigravida.
Maternal breath holding.
Most dangerous stage for the baby.
describe stage 3 of labour
Stage 3: Expulsion of placenta.
The uterus continues to contract until the placenta and membranes are delivered.
Lasts 10min.
Uterus cannot contract down effectively until the placenta is removed.
Women with retained pieces of placenta are at risk of …
Women with retained pieces of placenta are at risk of postpartum haemorrhage.
3 factors which influence the time fo delivery?
Light/dark cycle
Food supply
Infection
Indications for C section include ….
Indications for C section include
- cephalic-pelvic disproportion,
- FGR and evidence of acute fetal distress,
- previous C-section or uterine damage.
Indications for induced delivery;
(2)
Methods of induction are either….
Indications for induced delivery;
membranes ruptured >72h, overdue >10days.
Methods of induction are either endocrine or mechanical.
fat
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