Small for Dates Pregnancy Flashcards
What are the two main causes of a small for dates pregnancy?
Preterm delivery, and being small for gestational age
What is the definition of preterm delivery?
Delivery earlier than 37 weeks gestation
What are some causes for a small for gestational age pregnancy?
IUGR and being constitutionally small
At what point is a foetus viable?
24 weeks
Define the following: a) extreme preterm? b) very preterm? c) moderate-late preterm?
a) 24-27+6 weeks b) 28-31+6 weeks c) 32-36+6 weeks
What is the long-term survival outcome of a foetus born at a) 24 weeks? b) 26 weeks?
a) 40% b) 77%
What are the survival outcomes of a preterm baby born beyond 32 weeks?
> 95%, essentially the same as for a baby born at term
What are some general groups of causes of preterm birth?
Infection, over-distension, vascular, intercurrent illness, cervical incompetence, idiopathic
What are some factors which may cause over-distension of the uterus leading to preterm birth?
Multiple pregnancy, polyhydramnios
What is a vascular cause which may result in preterm birth?
Placental abruption
What is the strongest risk factor for preterm birth?
The mother has already had a baby born preterm (20% risk if once, 40% risk if twice)
What social factors are risk factors for preterm birth?
Poor socioeconomic status, smoking, drug use (especially cocaine)
In what ethnic group is preterm birth more common in?
Black women
What are some risk factors for preterm birth relating to a) age of the mother? b) weight of the mother? c) parity of the mother?
a) young age (i.e. teenage) b) low BMI c) parity 0 or > 5
How does preterm labour present?
Painful contractions and backache +/- vaginal discharge
Preterm labour with bleeding suggests what might be the underlying cause?
Antepartum haemorrhage
Preterm labour with loss of lots of fluid vaginally suggests what might be the underlying cause?
Preterm premature rupture of membranes (P-PROM)
A small for gestational age foetus can be identified based on what?
Antenatal risk factors and screening during antenatal care
What is the definition of small for gestational age?
An abdominal circumference or estimated foetal weight below the 10th centile on a growth chart
If you have a suspicion of SGA, what investigation is used to give an estimate of foetal size which can give an estimate of foetal weight?
Ultrasound
What is the relationship between SGA and IUGR?
They are not the same thing, though IUGR is more common in foetuses which are SGA than foetuses which are not
What is intra-uterine growth restriction?
There is failure of the foetus to achieve its full growth potential, baby is on a lower centile than would be expected
What is seen in a) symmetrical IUGR? b) asymmetrical IUGR?
a) small head and small abdomen b) normal head and small abdomen
Why does asymmetrical IUGR occur? What are some diagnoses that this may suggest?
Because the baby is preserving brain growth and development at the cost of other organs. Could point towards a chromosomal abnormality or placental problem.
What defines a low birth weight?
A baby born < 2.5kg regardless of gestation
What is the relationship between maternal age and SGA?
SGA is more common in older mothers
If there are major antenatal risk factors for SGA present, what is the management?
Serial US scans usually every 4 weeks until delivery to monitor growth
If there are minor antenatal risk factors for SGA present, what is the management?
At around 20 weeks, perform a uterine artery Doppler to see how well the placenta is being perfused. If this is poor, serial scanning should be started as for major risk factors.
What is the main way of assessing for SGA during normal antenatal screening?
Measurement of symphysial-fundal height, done from 24 weeks
If there is any single measurement of symphysial-fundal height which falls below the 10th centile on a personalised growth chart, what should be done?
US growth scan
Serial measurements of symphysial-fundal height below the 10th centile suggests what?
Slow/static growth
What factors are comprised to form a personalised foetal growth chart? How many centiles are there?
Mothers ethnicity, parity and BMI. Forms a 90th, 50th and 10th centile line.
What is the primary way of diagnosing SGA? How is this done?
A measure of estimated foetal weight. Done by measuring abdominal circumference, head circumference and femur length
What are some additional investigations that can be done to assess for SGA?
Liquor volume/amniotic fluid index or uterine/umbilical artery Doppler
What are some clinical features of poor growth?
Predisposing factors present, reduced liquor, fundal height < expected, reduced foetal movements
What are some maternal factors which could cause SGA?
Poor lifestyle, abnormal BMI (low or high), increased age, maternal disease e.g. hypertension
What investigation can be used to assess maternal risk of hypertension?
Uterine artery Doppler
What are some placental factors which could cause SGA? What is this often secondary to?
Infarcts or abruption, often secondary to hypertension
What are some foetal factors which could cause SGA?
Infection, congenital abnormalities, chromosomal abnormalities
What is the major risk of IUGR antenatally and during labour?
Risk of hypoxia and/or death
What are some risks postnatally of IUGR?
Hypoglycaemia, asphyxia, hypothermia, polycythaemia, hyperbilirubinaemia
What are some risks of IUGR as the child gets older?
Failure to reach milestones, cerebral palsy, short stature in adulthood
What are the 4 main ways of assessing the wellbeing of a small for dates pregnancy?
Assessment of growth with serial scans and growth chart plotting, cardiotocography, biophysical assessment and Doppler use
When can cardiotocography be performed? What does this do?
Beyond 28 weeks, records foetal heartbeat and uterine contractions
When should a cardiotocography be performed for a small for dates foetus?
If there is reduced foetal movements and reduced liquor
If a small for dates pregnancy has an abnormal cardiotocography, what should be done?
Early delivery
What is a biophysical assessment for a small for dates foetus?
An ultrasound assessment which takes up to 20 mins and considers movement, tone, foetal breathing and liquor volume
If all is well, a small for dates foetus should be delivered when?
By 37 weeks
What are some indications for considering early delivery in a small for dates pregnancy?
Static growth, abnormal umbilical artery Doppler, normal umbilical artery Doppler with abnormal MCA between 32-37 weeks, abnormal umbilical artery Doppler with abnormal ductus venosus Doppler between 24-32 weeks
If early delivery is being planned of a small for dates foetus, what are the two most important things to give them?
Steroids and magnesium sulphate
Why should steroids be given when planning early delivery?
To increase lung maturity
Why should magnesium sulphate be given when planning early delivery? How is it given?
Given as a 4 hour infusion before delivery to provide foetal neuroprotection
Magnesium sulphate should be given when planning a delivery up to when?
34 weeks
Overall, the management and timing of delivery of a small for dates foetus is a balance between what?
The risks of prematurity and the potential of hypoxia in utero or stillbirth
Both umbilical and uterine artery Dopplers measure what?
Placental resistance to blood flow would be expected to be what?
Why should these investigations only be performed beyond 20 weeks?
Resistance to blood flow to the placenta (i.e. amount of blood flow to the placenta)
Expected to be low resistance
Because at the start of pregnancy, resistance of flow to the placenta is physiologically high so can give false positive results
What is a uterine artery Doppler used for?
When should it be performed?
An abnormal uterine artery Doppler is only worrying when?
It is a screening test to detect increased risk of pre-eclampsia and IUGR in a high risk population
20-24 weeks
When it is abnormal on both the left and right sides
This is a uterine artery Doppler. What does it show and what does this suggest?
Shows a notch in diastole which suggests high resistance to flow through the uterine artery to the placenta
What is an umbilical artery Doppler used for?
When is an umbilical artery Doppler performed?
To detect foetuses previously diagnosed with SGA that are at significant risk of perinatal morbidity and mortality due to growth retardation
> 24 weeks
Describe what is being seen in umbilical artery Dopplers A, B and C?
A = normal (low resistance to flow)
B = developing resistance to flow
C = high resistance to flow - reversed flow (i.e. blood is going back the way in diastole)
If there is an abnormal umbilical artery Doppler in an SGA foetus, what further investigations can be done?
When can these be performed?
What are these assessing?
MCA and ductus venosus Dopplers
MCA = 32+ weeks / DV = 24-32 weeks
Assessing if there are brain sparing effects or not
