17 - Fetal Growth and Development

Question 1

What is the fetal period?

Answer 1

• 9 weeks to term
• Lots of weight gain and growth and the fetus gets bigger than placenta

Question 2

What is crown rump length?

Answer 2

Length of fetus from head to tail, used mainly in early pregnancy as increases dramatically

Question 3

In the different periods of embryonic growth, what tissue contributes most to the weight of the fetus?

Answer 3

- Early fetal: protein due to muscle development

- Late fetal: adipose for metabolic purposes and heat regulation

Question 4

What are the body proportions of the fetus as it moves through each period?

Answer 4

At first the head is 50% of the length of the fetus, but goes to 25% by birth

Question 5

What are the different ways that we can assess fetal wellbeing?

Answer 5

• Ask mother about fetal movements around 20 weeks

- Symphis fundal height is non invasive

- Ultrasound scan

Question 6

How do we measure symphysis fundal height and why may it not correlate to weeks of gestation?

Answer 6

• After 20 weeks the week of the pregnancy should roughly equal the number of cm measurement e.g 28cm at 28 weeks
• May not correlate as may be oligohydraminos, IUGR, fetal head dropping into pelvis, polyhydraminos from swallowing difficulties or urine production issues

Question 7

What can an ultrasound scan be used to image in the fetus?

Answer 7

• Estimate date of pregnancy
• Rule out ectopics
• Identify multiple pregnancies
• Measure fetal growth at 20 weeks and any anomolies

Done at 20 weeks as structures have developed and are big enough to be seen at this point

Question 8

How can we estimate fetal age?

Answer 8

- LMP: date of last menstrual period prone to inaccuracy

- Developmental criteria:

CRL: good way to date from 7 to 13 weeks as linear growth

Biparietal Diameter: distance between parietal bones in second and third trimester

Abdominal circumference: used with above in second and third trimester. Often used in conjuction with femur length

Question 9

What is the average birth weight of babies?

Answer 9

3500g

• >4500g macrosomia
• <2500g suggest growth restriction

Question 10

Why may a baby have a low birth weight?

Answer 10

• Premature
• Constitutionally small (e.g mother is small)
• Growth restriction

(high birth weight usually due to gestational diabetes)

Question 11

What are the different stages of the development of the respiratory system in the fetus?

Answer 11

- Embryonic period: outpouching of foregut to create bronchopulmonary tree

- Week 8-16: Pseudoglandular stage. Duct system begins to form forming bronchioles

• Week 16 - 26: Canalicular stage where respiratory bronchioles are forming, still no alveoli

- Week 26 - Term: Terminal sacs at the end of respiratory bronchioles. Differentiation of type I and type II pneumocytes so surfactant

Question 12

What determines fetal viability and what would you do if you had to deliver a baby before this point?

Answer 12

• Viabity depends if pneumocytes are present or not so when enter terminal sac stage at 24 weeks
• If need to deliver early give mother glucocorticoids to try and stimulate surfactant production

Question 13

What is the normal fetal heartbeat and why is it important to know this?

Answer 13

• 110 to 160 bpm
• Fetal bradycardia can mean fetal distress

Question 14

What are some causes of oligo and polyhydraminos?

Answer 14

• Urine production starts week 10
• Oligo: renal impairment, placental insufficiency

- Poly: CNS defect, tracheo-oesophageal fistual, inability to swallow

Question 15

How long does the development of the nervous system take?

Answer 15

• First and last

- Corticospinal tracts needed for voluntary movements start to develop in the 4th month

• Myelination of brain and these tracts still occuring after birth up to 1 year so increase in infant mobility

Question 16

Why and when do babies start moving in utero?

Answer 16

• Need to practice for independent life after birth, e.g suckling thumb
• Mother feels quickening around 17 weeks but first movement is probably around 8 weeks

Question 17

As the gravid uterus rests on the pelvic brim it may compress the ureters, what issues can this cause?

Answer 17

• Hydronephrosis
• Kidney stones
• Prone to UTIs as stasis

Question 18

What hormone causes a change in maternal carbohydrate metabolism?

Answer 18

• human placental lactogen
• increases insulin resistance

Question 19

What are some complications of poorly controlled gestational diabetes?

Answer 19

• Preeclampsia
• Risk of type II DM in baby and mother
• Still birth
• Jaundice
• Hypoglycemia at birth

Question 20

What signs and symptoms suggest pre-eclampsia is worsening in severity?

Answer 20

• Examine optic fundi for cerebral oedema
• Examine tendon reflexes for hyperreflexaemia

Question 21

What is normal fetal pO₂?

Answer 21

4kPa

Question 22

What prenatal diagnostic test has the highest risk of pregnancy loss?

Answer 22

Chorionic villus sampling

Question 23

What does symmetrical intrauterine growth restriction (both the head circumference and abdominal circumference are lower than normal) suggest?

Answer 23