Fetal Growth - Assessment Flashcards
What are the stages of fetal growth?
1) Stage 1 (hyperplasia) - 4-20 weeks - rapid mitosis and increase of DNA content
2) Stage 2 (hyperplasia and hypertrophy) - 20-28 weeks - declining mitosis with increase in cell size
3) Stage 3 (hypertrophy) - 28-40 weeks - rapid increase in cell size (peak velocity 33 weeks), rapid accumulation of fat, muscle, connective tissue
When does 95% of fetal weight gain occur?
During the second half of pregnancy (> 20 weeks)
What is the crown-rump length at 8 weeks vs 32 weeks?
- 8 weeks = 3cm
- 32 weeks = 30cm+
When do you stop measuring crown rump length (CRL) and why?
Don’t measure past 12 weeks bc can’t get the whole baby on the screen
When is the greatest weight increase?
Third trimester
Roughly what is the fetal weight at 8, 12, 26 and 38 weeks?
- 8 weeks = 3g
- 12 weeks = 90g
- 26 weeks = 1200g
- 38 weeks = 3350g
In which trimester is there the most variation/wider range in weight?
3rd trimester
How is growth assessed?
Using ultrasound
Describe the aims of the first trimester ultrasound scan
- Routine scan approx. 12 weeks from LMP
- Checking for heart beat (viability)
- Checking if single fetus or multiple
- Measurement of CRL - used to date pregnancy
- Also offer combined screening for trisomies
What is the crown rump length?
The distance between the top of the head (crown) and the bottom of the buttocks (rump)
How is the pregnancy dated in the first ultrasound scan?
1) CRL 45-84mm = 11+2-14+2 weeks
2) If CRL > 84.1mm, date by head circumference
What are the aims of the ultrasound assessment in the second trimester?
- Routine anomaly scan
- 18-20 weeks
- Assess fetal growth, fetal anomalies, placental site e.g. close to cervix
What is measured to assess fetal growth/biometry in the second ultrasound scan?
1) Head circumference (HC)
2) Bi-parietal diameter (BPD)
3) Abdominal circumference (AC)
4) Femur length (FL)
5) Combine to estimate fetal weight (EFW)
How should the US look to accurately measure abdominal circumference?
- Should see only one rib and should be circle shape
- If see multiple ribs or more oval, need to move the probe so it is clearer
How should you measure femur length on an US?
Get the longest possible length by moving the probe
How is fetal growth assessed without imaging?
Symphysial fundal height (SFH)
How do you measure SFH to assess fetal growth?
- Use a tape measure upside down so the numbers are hidden
- Measure from the fundus (variable) to the symphysis (fixed)
What is the link between gestational age and the SFH?
SFH = gestational age ± 2cm
- Linear relationship
Where should the fundus be at 20 weeks?
Umbilicus
What is measurement of SFH used for?
To tell if a baby is growing properly and the amount of amniotic fluid
When does the link between SFH and gestational age not work?
1) Multiple pregnancies (would therefore scan them more often)
2) Morbid obesity
How is a customised growth chart (GROW) different?
Baby’s expected growth is adjusted for factors e.g. mother’s DoB, ethnicity, parity, heigh, booking weight and BMI
What is done in the second/third trimester growth scan if there are concerns about growth?
1) Biometry - HC, BPD, AC, FL
2) Amniotic fluid index (AFI)
3) Umbilical artery and middle cerebral artery doppler
How is an amniotic fluid index used to assess fetal growth?
- Check women’s water hasn’t gone yet
- If this decreases, might suggest placenta malfunction
- If this is normal then it is a healthy small baby
How is an umbilical artery fetal doppler used to assess fetal growth?
- Looks at waveform from placenta to baby
- Want to check blood is flowing in right direction
- If blood is going back and forward - deliver baby, ominous sign
How is a middle cerebral artery fetal doppler used to assess fetal growth?
- Sign of redistribution is concerning - low reading is concerning as distributing more blood to its brain
