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.
