Obstetrics: Foetal Growth, Lie, Presentation Flashcards
When does foetal growth monitoring begin?
24 weeks
How can foetal growth be measured clinically?
Using examination techniques:
- Abdominal palpation of fundal height (only detects about 20% of growth abnormalities)
- Symphysis-fundal height measurement
Ultrasound assessment (90% accurate)
How can you roughly date a pregnancy using fundal height?
12 weeks- fundus just above pubic bone
14 to 16- midway between pubic bone and belly button
20- belly button
36-38- fundus right under the sternum
When do patients receive regular US monitoring of foetal growth?
- High risk patients
- Low risk patients where a growth issue is suspected.
What measurements does a US foetal growth scan use?
- Head circumference and biparietal diameter
- Abdominal circumference
- Femur length
Combines all 3 to produce a single value.
What does ‘small for GA’ or ‘large for GA’ actually mean?
Simply describe position of foetal measurements on a gestational population centile chart, DO NOT IMPLY PATHOLOGY.
SGA = Anthropometric variables below the 10th centile
LGA = Measurements above the 95th
Why are we concerned about SGA babies?
Small babies contribute disproportionately to perinatal morbidity and mortality.
This is because while some babies are naturally smaller, many are smaller due to pathological reasons which also put them at later risk e.g. IU hypoxia, acidaemia, prematurity.
What is the difference between SGA and IUGR?
SGA just means small vs population.
IUGR means small vs genetic growth potential, more likely to indicate pathology.
What are the risk factors for growth restricted babies?
Background factors:
- Extremes of age
- Extremes of BMI
- Smoking, alcohol, drug use
- Domestic violence
- Prescription or OTC drug use
Obs factors:
- Previous FGR (biggest risk)
- Recurrent foetal loss (second biggest risk)
- Raised AFP
- Infection
- Placental pathology
Conditions associated with IUGR:
- Hypertension
- Haemoglobinopathy
- Antiphospholipid syndrome
- Collagen vascular syndrome
- Renal disease
What management does a woman referred to clinic with a potentially small baby require?
1) Confirm that the baby is actually small
2) Establish cause of small foetus
3) Devise management plan for monitoring the small baby
4) Work out a delivery plan (timing + mode), discuss risk and benefits with patient
How do you confirm that the baby is actually small?
- First, confirm that the dates used are actually correct, baby hasn’t been dated as older than expected
- Assess growth by USS
- Review measurements (i.e. individual measurements that make up the scan, one might have been mistaken)
What are the causes of a small baby?
WAINS:
- Wrong small (inaccurate measurements, wrong dates)
- Abnormal small (chromosomal abnormality, syndromic issue, congenital malformations)
- Infected small (IU infection e.g. CMV)
- Normal small (constitutionally small, healthy baby)
- Starved small (placental FGR e.g; poor placentation, smoking, maternal disease affecting placenta, multiple pregnancies)
What is the most common cause of small for date babies?
Starved small- Placental FGR.
What 3 factors are necessary for adequate placental blood delivery?
1) Good Uteroplacental blood flow (uterine artery to placenta)
2) Good fetoplacental blood flow (from placenta to umbilical arteries)
3) Functioning villous structure at the interface of maternal and foetal blood.
How can successful trophoblast invasion (one of the necessary components of a functioning placenta) be measured clinically?
Uterine artery Doppler, normally done between 20-24 weeks.
Look for low resistance wave form.
How would you manage a baby with abnormal uterine artery doppler results?
Serial growth scans.
What sonographic factors can help differentiate between a normal small baby and a baby with some sort of growth restriction?
- Centile position (both 9th and 1st are SGA, 1st is much more likely to be FGR)
- Symmetry (e.g. head size vs abdominal size which is a measure of liver growth)
- Liquor volume
- UMA Doppler (indicator of placental function)
- Growth velocity (plateauing is a strong indicator of GR)
Essentially 3 measures:
- Growth (symmetry + velocity)
- Amniotic fluid
- Foetal well-being (UMA doppler)
What would the sonographic report for a healthy SGA baby look like?
Growth = Symmetrical and normal velocity
Amniotic fluid = Normal
Foetal well-being = Normal UMA Doppler
What would the sonographic report for a aneuploidy or infection restricted baby look like?
Growth = Markedly small, Reduced velocity, Usually symmetrical growth
Amniotic fluid = Usually normal but can be increased
Well-being = Normal Doppler
What would the sonographic report for a placental UGR baby look like?
Growth = Often asymmetrical, Reduced velocity
Amniotic fluid = Usually reduced
Foetal well-being = High resistance UMA flow, Decreased BPP score
Why are serial scans so important in SGA babies?
Things like asymmetry may only develop later in the pregnancy, need to pick these up and judge management around them.
How do you monitor a mother with a confirmed SGA baby, once potential causes have been investigated?
Maternal monitoring:
- Assess for any modifiable factors e.g. smoking
- Assess for the presence of maternal disease
- Continue monitoring for pre-eclampsia at regular intervals
Foetal surveillance:
- Growth measurements every 2-4 weeks
- Foetal wellbeing surveillance (Foetal and UMA Doppler, amniotic volume measurements, biophysical profile, maternal perception of foetal movements)
What are the different Dopplers used in antenatal scans?
Uterine artery doppler:
- Illustrates remodelling and conversion into high flow low pressure vessels
- Useful for screening, performed at 20 weeks
- Identifies high risk patients
- NOT useful for surveillance
Umbilical Artery Doppler (UMA Doppler):
- Reflects increases in placental resistance
- Essential in the surveillance of GR foetuses
MCA and Venous Doppler can be used as additional measures of foetal health/ blood flow.
How is the delivery of a SGA baby managed?
If umbilical artery Doppler is normal, delay delivery until at least 37 weeks.
If AREDF (absent or reversed end-diastolic flow in the umbilical artery), consider delivery if past 34 weeks, even with normal additional assessments
If AREDF + abnormal CTG/BPP/ other Doppler parameters, deliver before 34 weeks.
Simply: Normal Doppler, give the baby as long as possible. Abnormal Doppler, get the baby out ASAP (even faster if other issues).
What is an SGA baby at greater risk of post-delivery?
Increased risk of…
- PN death
- Increased need for resus
- Hypothermia
- Hypoglycaemia
- RDS
- NEC
- Neurodevelopmental disability
- Cerebral palsy
+ a number of adult conditions.
How do you investigate an LGA baby?
- Establish correct dates!!
- If suspected LGA is based off fundal height measurements, consider USS to rule out other causes of large uterus e.g. uterine fibroids, pelvic mass, polyhydramnios, maternal obesity
- Exclude maternal diabetes (GTT before 34 weeks)
- Exclude polyhydramnios
What are some causes of LGA babies?
Maternal factors:
- Diabetes
- Obesity
- Increased maternal age
- Multiparity
- Large stature
Foetal factors:
- Constitutional
- Male gender
- Post-maturity
- Genetic disorders (Beckwith Wiedeman)
What risks are associated with LGA babies?
Maternal risks:
- Prolonged labour
- Operative delivery
- Postpartum haemorrhage (overly distended uterus)
- Genital tract trauma
Foetal risks:
- Birth injury
- PN asphyxia due to difficult delivery
- Shoulder dystocia and Erb’s palsy
- Hypoglycaemia (and seizures)
- Childhood obesity
- Adult Metabolic syndrome
How do you manage an LGA baby?
- Exclude maternal diabetes and polyhydramnios
- If maternal diabetes + macrosomia, offer C section
- If no Diabetes, no benefit from CS or induction so plan for normal delivery
- w/ early recourse to intervention if delay in labour AND prepare for shoulder dystocia by having someone on hand specialised in delivering larger babies.
