Foetal Growth and Development Flashcards
How long does the pre embryonic, embryonic and foetal period last and what occurs in each
Pre-embryonic period – 1-2 weeks – formation of germ layers
Embryonic period – 3-8 weeks – formation of systems
Foetal period – 9-38 weeks
The foetal period - growth and physiological maturation of the structures created during the much shorter embryonic period This period involves preparation for the transition to independent life after birth.
How long does pregnancy normally last?
Terms is usually stated to be 38 weeks. However pregnancy is measured from last date of last menstrual period so we must add 2 weeks giving 40 pregnancy weeks.
Describe the growth pattern of the embryonic period?
Embryonic period is characterised by intense activity – organogenetic period but absolute growth is very small – except placenta! Growth & weight gain accelerate in foetal period.
What is the CRL and how does it change throughout foetal growth? What happens in the early and late foetal periods.
CRL (crown rump length) increases rapidly in the pre-embryonic, embryonic & early foetal periods. Weight gain is slow at first, then increases rapidly in mid- and late foetal periods. Early foetus – protein deposition. Late foetus – adipose deposition.
How do body proportions change through the foetus’ life?
Body proportions change dramatically during the foetal period – at 9 week, the head is approx half-crown-rump length – thereafter, body length & lower limb growth accelerates.
What happens in antenatal assessments of the foetus?
Mother – Foetal movements, regular measurements of uterine expansion – Symphysis-fundal height and ultrasound scan. Obstetric Ultrasound scan (USS). This is safe, can be used early in pregnancy to calculate age also: rule out ectopic, number of foetuses etc. Routinely carried out at 20 weeks to assess foetal growth and Foetal anomalies.
How can you estimate a foetus’ age?
Last menstrual period but this is prone to inaccuracy due to cycle length discrepancy and break through bleeding at implantation.
Crown-rump length (CRL). Measured between 7 & 13 weeks to date the pregnancy and estimate EDD. Scan in T1 also used to check location, number, viability. Becomes less accurate outside these dates.
Biparietal diameter – the distance between the parietal bones of the foetal skull which is used in combination with other measurements to date pregnancies in T2 & T3. Abdominal circumference & femur length. AC &FL used in combination with BPD for dating and growth monitoring also useful for anomaly detection.
What is a normal baby weight?
3500 g is considered average, < 2500 g suggests growth restriction, > 4500 g is macrosomia – maternal diabetes. Many factors influence birth weight, not all pathological.
Why is accurate dating of the babies age important?
Babies can have low birth-weight because: they are premature or they are constitutionally small (small mum small baby) or they have suffered growth restriction associated with neonatal morbidity & mortality.
When do the lungs develop?
The lungs develop relatively late. Embryonic development creates only the bronchopulmonary tree – Functional specialisation occurs in the foetal period this has major implications for pre-term survival.
Describe the process that forms alveoli
Weeks 8 – 16: Pseudoglandular stage – duct system begins to form within the bronchopulmonary segments created during the embryonic period – bronchioles form from bronchiolar buds surrounded by mesenchyme. These are lined by columnar epithelium.
Weeks 16 – 26: Canalicular stage – formation of respiratory bronchioles – Budding from bronchioles formed during the pseudoglandular stage. Some ciliated cuboidal epithelium begins to arise.
Weeks 26 – term: terminal sac stage – terminal sacs begin to bud from the respiratory bronchioles. Differentiation of – Type I & Type II pneumocytes forming surfactant.
How do lungs prepare themselves for birth and their first real breath?
Gas exchange conducted at placenta, but lungs must be prepared to assume full burden at birth so “breathing” movements – conditioning of the respiratory musculature. Fluid filled – crucial for normal lung development.
What implications does the development of lungs have on pre-term survival?
Threshold of viability cannot be continually pushed back since there is a limit beyond which the lungs will not be sufficiently developed to sustain life. Viability is only a possibility once the lungs have entered the terminal sac stage of development – i.e. > 24 weeks.
What is respiratory distress syndrome?
Respiratory distress syndrome often affects infants born pre-maturely. Insufficient surfactant production so if pre-term delivery is unavoidable or inevitable – glucocorticoid treatment (of the mother) – increases surfactant production in foetus.
What is normal foetal heart rate?
. The definitive foetal H/R (110-140) is achieved at around 15 weeks foetal bradycardia is associated with foetal demise.
