7.1: Fetal development

Question 1

Define the ‘fetal period’ and when it occurs

Answer 1

End of 8th week-term.

Growth and maturation of structures created during the embryonic period, preparing for transition to independent life

Question 2

How long are the following stages?

a) pre-embyronic
b) embryonic
c) fetal

Answer 2

a) 1-2 weeks
b) 2-8/9 weeks
c) 9-38 weeks

Question 3

Describe the development occurring during the embryonic period

Answer 3

Organogenetic period: three germ layers -> major organs

Small absolute growth other than placenta

Question 4

Describe the growth pattern of weight gain. In which stage/period does maximum growth and weight gain occur?

Answer 4

Slow initially -> increases rapidly in mid-late fetal periods first with deposition of protein and later adipose in
subcutaneous and abdominal stores

Question 5

What is the CRL and what can it be used for? What is its growth pattern?

Answer 5

Crown-rump length; estimates EDD

Increases rapidly in all three periods

Question 6

What is the metabolic and growth significance of the following stages?

a) embryo
b) early fetus
c) late fetus

Answer 6

a) Morphogenesis and differentiation, small weight gain but sig. placental growth
b) protein deposition
c) adipose deposition

Question 7

List three things that can be used to perform an ante-natal assessment of the fetus and when they might be used

Answer 7

1. 1st trimester: USS
2. ~17 wks onwards asking mother if she’s felt fetal movements
3. 2nd and 3rd tri: measure uterine expansion (symphysis-fundal height)

Question 8

When are obstetric ultrasound scans routinely carried out and what two major things can they assess for?

Answer 8

12 and 20 weeks; Fetal growth and anomalies

Question 9

How would you provide an EDD to a patient?

Answer 9

Provide the one calculated by the scan (even if the woman says it doesn’t line up with her LMP) unless its an IVF

Question 10

What is the biparietal diameter? What can it be used for and when?

Answer 10

Distance between parietal bones of the fetal skull, used with other measurements (i.e femur length, abdominal circumference) to date pregnancies and determine any anomalies in T2 and T3

Question 11

What is the general classification of birth weights (average, growth restriction and macrosomia)?

Answer 11

Average 3kg
Growth restriction <2.5 kg
Macrosomia >4.5 kg

Question 12

Name 3 general reasons for a baby having a low birth weight

Answer 12

1. Premature
2. Constitutionally small
3. Growth restriction

Question 13

Why is it important for a baby to be delivered at ‘40+12’ weeks

Answer 13

1. Placental bloodflow becomes more compromised

2. Increased risk of stillbirth

Question 14

When does the respiratory system develop in relation to other systems? When is the bronchopulmonary tree formed and when does functional specialization occur?

Answer 14

Later

1. Embryonic development creates the bronchopulmonary tree
2. Functional specialization occurs in the fetal period

Question 15

What does the lung/respiratory bud arise from and what structure is responsible for separating the trachea and esophagus?

Answer 15

Resp diverticulum (pouches off the esophagus) -> lung bud

Tracheoesophageal septum

Question 16

What is a complication of a tracheoesophageal fistula, how and how might this be recognized once the baby is born?

Answer 16

Amniotic fluid doesn’t pass normally through GI tract -> accumulates in lungs -> polyhydramnios

Can make breathing difficult

Question 17

Where does gas exchange occur before the baby is born and why? What ‘bodily preparations’ are made in the fetus to assist the lungs in taking over?

Answer 17

Conducted at the placenta (as the developing lungs are fluid-filled, but lungs must be prepared to assume the full burden at birth). The respiratory musculature is pre-conditioned so the baby undergoes “breathing movements” before it is born

Question 18

What are the fetal implications when the mother has anhydramnios?

Answer 18

Lack of amniotic fluid

• > underdeveloped baby lungs
• > baby can’t move around comfortably -> may develop contractures

Question 19

What determines the ‘threshold of viability’ of how early a baby can be delivered?

Answer 19

Determined by whether lungs have entered TERMINAL SAC stage of development (sufficiently developed to sustain life)

*baby should also be >5kg

Question 20

What causes respiratory distress syndrome and what can be given to prevent this?

Answer 20

Premature birth -> insufficient surfactant produced.

If pre-term delivery is unavoidable: give dexamethasone injections to increase surfactant production

Question 21

What is the functional fetal kidney called? When does it begin functioning and what happens if it is dysfunctional?

Answer 21

Metanephros begins functioning at week 10,

Dysfunctional: Oligohydramnios occurs as fetal urine is a major contributor to amniotic fluid volume

Question 22

What abnormalities is oligohydramnios suggestive of?

Answer 22

1. Reduced renal function
2. Placental insufficiency; i.e pre-eclampsia: blood is redistributed to fetal brain rather than the abdomen and kidneys -> poor urine output

Question 23

What two things must be checked if a woman presents with oligohydramnios?

Answer 23

1. Ensure fetal growth isn’t restricted (i.e if cause relates to placental insufficiency)
2. Check membrane hasn’t been ruptured

Question 24

Why is polyhydramnios associated with diabetic moms?

Answer 24

Abundant glucose -> baby grows and pees more

Question 25

Name 3 potential complications for birth when the mother has polyhydramnios

Answer 25

Excessive pressure …

• > Placental rupture
• > uterus stretches quicker -> contracts early -> early labour

Excessive fluid…

• > baby can move more freely in uterus -> baby may be in abnormal position when water breaks
• > Gushing pressure -> baby limb (still attached) and cord can come out of cervix with water

Question 26

When does the CNS develop in relation to other systems? Name four major structural CNS changes that occur

Answer 26

First to begin and last to finish

1. Cerebral hemisphere becomes largest part of brain
2. Histological differentiation of cortex in the cerebrum and cerebellum
3. Formation and myelination of nuclei and tracts
4. Growth of spinal cord and vertebral column

Question 27

How do fetal sensory and motor systems develop?

*sensations, pain and movement

Answer 27

Sensory: hearing and taste mature before vision

Ascending tracts for pain are present but not myelinated at 19 weeks

Fetal movements can be detected by USS at 8 weeks (repertoire of movements develop to help baby “practice” for postnatal life, i.e suckling, breathing, etc)

Question 28

Name 5 tests that can monitor changes of the fetus’ anatomical and physiological parameters

Answer 28

1. Ultrasound
2. Fetal movements kick chart
3. Doppler ultrasound
4. Non-stress tests; NST monitors HR changes associated with fetal movements
5. Biophysical profiles

Question 29

When is a fetus regarded as having ‘growth restriction’? What are the two main types of growth restriction?

Answer 29

When their estimated weight is below the 10th percentile for their gestational age

1. Symmetrical: growth restriction is generalized and proportional
2. Asymmetrical: abdominal and head growth lags

Question 30

How might you determine the duration of the pregnancy? (2 things)

Answer 30

Fertilization age, LMP

Question 31

List 5 measurements/predictions that can be made in utero by ultrasound

Answer 31

CRL, foot length, biparietal diameter, weight and appearance after delivery

Question 32

What is the symphysis fundal height and what can it help determine?

Answer 32

Distance between symphysis pubis to the top of the uterus (i.e fundus).
A lag suggests intrauterine growth restriction

Question 33

Briefly describe the four histological stages of lung development

Answer 33

1. Pseudoglandular: 8-16 weeks, duct system forms up to terminal bronchioles
2. Canalicular: 16th-26th weeks, bronchioles bud off, some terminal sacs, more vascular and pseudostratified ciliated columnar epithelia are forming
3. Terminal Sac: 26 week- Term: surfactant formed, many terminal sacs and some primitive alveoli
4. Alveolar period: last weeks of pregnancy - 8 years, alveoli formed

Question 34

What happens to the fluid within the fetus’s lungs when it’s born?

Answer 34

Squeezed out in normal vaginal delivery, remaining is absorbed

Question 35

Name three defects/disorders associated with polyhydramnios

Answer 35

Esophageal or duodenal atresia, CNS abnormalities