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.
describe the fetal double bohr effect
image for initation of partuition in women:
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