Fetal Growth and Development Flashcards
What are the 3 stages of fetal developement?
- Pre-embryonic (weeks 1-2)
- Embryonic (weeks 3-8)
- Fetal (weeks 9-38)
How does fetal growth change throughout pregnancy?
- embryonic period - growth is very small but major body organs are developing
- fetal period - accelerated growth
How does the pattern of weight gain change throughout the fetal period?
Early fetal period- mainly protein from muscle development
Later fetal period- mainly adipose tissue for metabolic purposes and to regulate heart beat
What is the crown rump legnth? How does this increase throughout pregnancy?
The legnth of the fetus from head to tail
Increases linearly during the pre-embryonic, embryonic and early fetal periods
How does the body proportion of the fetus change during the fetal period?
Week 9- Head is ~ 1/2 CRL
After week 9, body and lower limb legnth accelerates
At birth - head is still 1/4 body legnth at birth
What measurements are taken at an ante-natal assessment of fetal well-being?
- Assess mother
- Fetal movements from 20 weeks onwards
- Regular measurements of uterine expansion → Symphysis- fundal height
- Ultrasound scan
How is symphisis- fundal height calculated?
Measured from the pubic symphysis to the height of the fundus
In what circumstances would the symphysis- fundal height not correlate to the gestational week?
-
Polyhydraminos ( a lot of amniotic fluid)
- happens if there are swallowing difficulties or exessive urine production
- Oligohydraminos (less amniotic fluid)
- Interuterine Growth Restriction
What can an ultrasound scan be used for in pregnancy assessment?
- Can estimate date of pregnancy
- Rule out ectopics
- Identify multiple pregnancies
- Routinely carried out at 20 weeks to assess fetal growth and check for any abnormalities
How can fetal age be calculated?
- Last Menstrual Period - easy to do but error prone
- Developmental Criteria - comparing USS measurements to ‘normal’ values
- Crown Rump Legnth - good between 7-13 weeks due to linear progression
- Biparietal diameter - distance between parietal bones of fetal skull used in the 2nd and 3rd Trimester
- Abdominal Circumference - Measures the widest part of the abdomen, often used in combo with femur legnth
What is the weight of an average fetus? What are ‘abnormal’ measurement classifications?
Normal weight- 3,500 g
<2,500 g suggests growth restriction
>4,500 g suggets macrosomia
Give some reasons why a baby may have a low birth weight?
- Baby is premature
- Constitutionally small as the mother is small
- Growth restriction
What is the most common cause of macrosomia?
Poorly controlled Gestational Diabetes
When do the lungs of the fetus develop?
Develop relatively late as not required for gas exchange until after delivery
How do the lungs develop?
- Develop as a divertculum of the foregut
- Separated by tracheoesophageal septum
- Budding/ branching of bronchioles begins weeks 8-16 in the pseudoglandular stage
- Respiratory bronchioles develop during canalucular stage weeks 16-26
- Terminal sacs develop from th ends of respiratory bronchioles at ~week 26
- Differentiation of Type I & II pneumocytes
Why are the lungs so important for pre-term survival?
The threshold of viability is 24 weeks
Viability is only possible once the lungs have entered terminal sac development
(Sets the current limit for threshold of termination of pregnancy)
What is the average fetal HR?
110-160bpm reached at around 15 weeks
When does fetal kidney function begin?
Week 10
What can cause oligohydraminos?
- placental insufficiency
- poor renal function of the fetus
What can cause polyhydraminos?
- Issues in co-ordinated swallowing (CNS defect)
- Congential abnormalies (trachea-osophageal fistula)
Which system of the body is most vulnerable to injury during development?
The Nervous System
What is required for coordinated voluntary movements in the fetus and when does this begin?
The corticospinal tract which develops from the 4th month of gestation
Myelination occurs only in the 9th month
If a baby in unable to co-ordinate their movements until 1 year after birth, what could have happened at birth?
The Myelination of the corticospinal tracts was incomplete
