S7) Foetal Growth and Development Flashcards
What is the foetal period and what happens during this?
- The foetal period is the period involving preparation for the transition to independent life after birth
- Growth and physiological maturation of the structures created during the embryonic period occurs
What characterises the embryonic period?
Embryonic period is characterised by intense activity (organogenetic period) but absolute growth is very small
What is crown-rump length?
Crown-rump length (CRL) is the measurement of the length of human embryos and fetuses from the top of the head (crown) to the bottom of the buttocks (rump)
Describe the differential growth observed in the crown-rump length
CRL increases rapidly in the pre-embryonic, embryonic & early fetal periods
Describe how weight gain varies in the different foetal periods
- Embryo – intense morphogenesis & differentiation; little weight gain; placental growth most significant
- Early foetus – protein deposition
- Late foetus – adipose deposition
Explain how body proportions change during the foetal period
- 9 weeks, the head is approx half crown-rump length
- Thereafter, body length & lower limb growth accelerates
Identify and describe 3 different ways of assessing foetal well-being
- Mother – foetal movements
- Regular measurements of uterine expansion – symphysis-fundal height
- Ultrasound scan
Obstetric ultrasound scan (USS) is routinely carried out at ~20 weeks.
Identify 5 advantages of this
- Safe
- Can be used early in pregnancy to calculate age
- Rules out ectopic pregnancy
- Indicates number of foetuses
- Assess foetal growth and anomalies
Identify and describe 2 different ways of estimating foetal age
- Last menstrual period (LMP) – prone to inaccuracy
- Developmental criteria – allows accurate estimation of fetal age
Why and when do we measure crown-rump length?
Measured between 7 & 13 weeks to date the pregnancy and estimate EDD
What is biparietal diameter and when is it used?
- Biparietal diameter is the distance between the parietal bones of the fetal skull
- Used in combination with other measurements to date pregnancies in T2 & T3
When is abdominal circumference and femur length used?
- AC & FL used in combination with BPD for dating and growth monitoring
- Useful for anomaly detection
How do we classify birth weights?
- Average: 3500 g
- Growth restriction: < 2500 g
- Macrosomia: > 4500 g (maternal diabetes)
Provide 3 possible reasons for low-birth weight
- They are premature
- They are constitutionally small
- They have suffered growth restriction (associated with neonatal morbidity & mortality)
The lungs develop relatively late.
Why is this?
- Embryonic development creates only the bronchopulmonary tree
- Functional specialisation occurs in the foetal period
Identify the different stages in the development of the respiratory system
- Weeks 8 – 16: pseudoglandular stage
- Weeks 16 – 26: canalicular stage
- Weeks 26 – term: terminal sac stage
Describe the pseudoglandular stage in lung development
- Duct system begins to form within the bronchopulmonary segments created during the embryonic period
- Forms bronchioles
Describe the canulicular stage in lung development
Formation of respiratory bronchioles through budding from bronchioles formed during the pseudoglandular stage
Describe the terminal sac stage in lung development
- Terminal sacs begin to bud from the respiratory bronchioles
- Type I & Type II pneumocytes differentiate
- Surfactant is produced
Gas exchange is conducted at placenta, but lungs must be prepared to assume full burden at birth.
How does this happen in T2 and T3?
- “Breathing” movements condition of the respiratory musculature
- Fluid filled spaces crucial for normal lung development
Discuss the threshold for viability in terms of pre-term survival
Viability is only a possibility once the lungs have entered the terminal sac stage of development (> 24 weeks)
Respiratory distress syndrome often affects infants born pre-maturely and involves insufficient surfactant production.
How can this be treated?
Glucocorticoid treatment (of the mother) increases surfactant production in foetus if preterm delivery is inevitable/unavoidable
When is the definitive foetal heart rate determined?
- The definitive fetal HR is achieved at around 15 weeks
- Foetal bradycardia is associated with fetal demise
Describe the development of the urinary system in the foetus and the importance of such
- Foetal kidney function begins in week 10
- Foetal urine is a major contributor to amniotic fluid volume
Describe the variations in amniotic fluid volume
- Oligohydramnios: too little amniotic fluid due to placental insufficiency or fetal renal impairment
- Polyhydramnios: too much amniotic fluid due to foetal abnormality e.g. inability to swallow
The nervous system is first to begin development and last to finish.
Briefly outline its development
- Corticospinal tracts required for coordinated voluntary movements to begin to form in the 4th month
- Myelination of brain only begins in 9th month
Outline the development of sensory and motor systems
- No movement until the 8th week
- Thereafter a large repertoire of movements develop to “practise” for post-natal life e.g. suckling, breathing
What is “quickening” and what is its the benefit?
- Quickening is the maternal awareness of fetal movements from 17 weeks onwards
- It is a low cost, simple method of ante-partum fetal surveillance and reveals those foetuses requiring follow-up
In terms of chronology, compare and contrast the development of the brain and lungs
Identify 3 benefits of transvaginal ultrasound
- Check that conceptus implanted in correct place
- Rule out ectopic pregnancy
- Check for multiple foetuses
Why are dietary supplements of folic acid recommended during pregnancy?
Folic acid prevents neural tube defects
When can you hear a foetal heartbeat with a:
- Doppler stethoscope
- Plain stethoscope
- Doppler stethoscope: 10-12 weeks
- Plain stethoscope: after 20 weeks
What is the average foetal heart rate at term?
110 - 160 bpm at term (37 weeks)
Which cells secrete surfactant?
Type II pneumocytes
At what gestational age does surfactant production begin and how is this significant in prematurity?
- Surfactant begins production at 24-28 weeks
- Majority of surfactant is produced by 35 weeks, hence is insufficient in premature babies
What is symphysis-fundal height ?
Symphysis-fundal height is the distance from the pubic symphysis and the fundus of the uterus used to assess foetal growth and development during pregnancy
Identify 3 sources of error for the symphysis-fundal assessment
- Human error (poor technique)
- More/less than normal amniotic fluid volume
- Later in pregnancy (foetal engagement, head moves, smaller fundus)
Which factors must be considered in deciding whether to allow a compromised foetus to remain in utero?
- Mother’s health
- Foetal viability
- Stage of pregnancy
How is amniotic fluid produced prior to week 8?
Amniotic fluid is produced by foetal cells in the amnion
Identify 5 conditions which would lead to decreased amniotic fluid volume
- Foetal kidney malfunction
- Maternal hypertensive disorders
- Premature rupture of membranes
- Foetal bladder outlet obstruction
- Premature leakage of amniotic fluid
The foetus swallows and digests amniotic fluid.
Identify a foetal GI tract defect that might lead to polyhydramnios
Defect in the tracheal oesophageal septum leads to blind-ended oesophagus (atresia) or fistula
Identify 5 instances when a foetus would be classified as at-risk
- Growth restriction
- Macrosomia
- Poorly positioned
- Multiple foetuses
- Pre-eclamptic mother
