Foetal Adaptations after Birth

What stimulates foetal lung growth in late pregnancy (3)?

• foetal breathing movements for 1-4hr / day during REM sleep

• breathing amniotic fluid - trains lungs to breath air

• distension stimulates growth

Why is it important that the late foetus has breathing movements while in utero (2)?

• breathing amniotic fluid trains lungs to breathe air

• stimulates growth

What is the purpose of surfactant?

reduces surface tension for inflation

What stimulates surfactant production?

cortisol

How is respiratory stress syndrome treated in premature infants?

surfactant

Why are antenatal’s treated with glucocorticoids?

accelerate lung development and surfactant production (stimulated by cortisol)

How are glucocorticoids administered to premature babies?

via a nebuliser (helps develop lungs)

What occurs in the late stages of foetal lung development (2)?

• foetal breathing movements = growth

• surfactant production

Why does the amount of glycogen in the foetal liver increase via to birth?

buffer to provide energy after birth while GI tract adapts to milk

What are the key points to remember about foetal circulation shunts (3)?

• incorporate placenta into circulation

• ensure appropriate delivery of oxygenated blood and nutrients to foetus

• largely bypass foetal lungs and liver

What are the 3 different shunts in the foetal circulation?

• ductus venosus (DV)

• foramen ovale (FO)

• ductus arteriosus (DA)

What are the 3 vessels found within the umbilical cord and what are their roles (2)?

• 2 arteries - from foetus to placenta with DEOXY blood

• 1 vein - returns from placenta with OXYGENATED blood

What is the function of the ductus arteriosus shunt?

joins pulmonary artery to aorta - bypasses lungs

What is the function of the foramen ovale shunt (2)?

• allows blood to pass from RHS of heart directly to LHS - ‘hole in the heart‘

• right atrium directly into left atrium

How does blood enter the heart?

oxygenated blood from placenta enters right atrium via inferior vena cava

What is the function of the ductus venosus shunt (2)?

• umbilical vein joins directly to vena cava to the heart

• bypasses hepatic circulation

Where is blood oxygenated in a foetus?

placenta

What % of the blood passes through the lungs in a foetus?

5%

Where do the foetal arteries in the umbilical cord branch from (2)?

• descending aorta splits into femoral arteries in groin area

• at point of split each artery branches off into the umbilicus

How does a foetus change from a foetal circulation to an adult circulation (5)?

• shunts shut at time of birth / time of first breathe

• loss of umbilical circulation

• fall in pulmonary vascular resistance

• pressure changes = transient reversal of flow through ductus arteriosus

• foramen ovale flap valve closes due to pressure changes

Which foetal shunt bypasses the lungs?

ductus arteriosus

Which foetal shunt bypasses the hepatic circulation?

ductus venosus

What % of the population has a hole in the heart and why does this occur?

5% - failure of foramen ovale to close properly

What are the 2 possible routes for oxygenated blood returning to the foetus via the umbilical vein?

• main route = ductus venosus into vena cava

• smaller = via liver into vena cava through hepatic veins

How is blood returning to the heart via the vena cava split into 2 streams and what are the 2 streams (3)?

• by the crista dividens (projects in foramen ovale)

• main stream = through foramen ovale into LHS, avoids lungs

• smaller = passes from RA to RV to lungs

What are the 2 possible routes for blood output from the right ventricle in the foetus?

• main route = through ductus arteriosus into aorta, bypasses lungs

• smaller = passes to foetal lungs

What is required for the maturation of the foetal cardiovascular system (2 hormones and their roles) (5)?

• decrease in prostaglandin E2 (normally maintains patent ductus arteriosus)

• cortisol stress response:

  • increases cardiac output

  • increases peripheral resistance

  • increases blood pressure

What hormone maintains the ductus arteriosus?

prostaglandin E2

How do pressure changes at the time of birth cause a change to an adult circulation (5)?

• fall in pulmonary resistance - lungs inflate with air = high pO₂

• pressure drops on RHS of heart

• pressure increases on LHS of heart

• transient reversal of flow through ductus arteriosus (high pO2 stimulates constriction)

• foramen ovale flap valve closes due to pressure reversal

How can constriction of the ductus arteriosus be inhibited (2)?

• low pO₂ (e.g. underdeveloped lungs in premature baby)

• high prostaglandin E2

How can patent ductus arteriosus be treated (failure of ductus arteriosus to close after birth) (2)?

• indomethacin (inhibits prostaglandin synthesis)

• has renal and GI side effects - balance of positives and negatives

What is foetal programming?

intrauterine environment of foetus can programme for development of chronic diseases in childhood / later life

What are some examples of intrauterine insults that can be linked to foetal programming (4)?

• hypoxia

• nutritional and prenatal stress

• glucocorticoids

• smoking

What evidence of foetal programming was found from the 1944 Dutch famine?

early exposure to malnutrition = higher blood pressure and coronary heart disease incidence

Why is it beginning to be thought that a natural birth could benefit a newborn compared to an elective caesarean (2)?

• natural birth can be many hours

• stress during this period has been found to properly set the stress response in the baby

What evidence of foetal programming was found using the Hertfordshire records from 1911-1930 (2)?

• lower birth weight = increased incidence of CHD and T2D

• high birth weight also showed link to increased CHD

What stage of foetal development exhibited the most striking effects of famine foetal programming?

early gestation (first trimester)

What was the impact of exposure to famine on early gestation foetuses from the 1944 Dutch famine (4)?

• 3 fold increase in CHD

• increased obesity

• altered clotting and atherogenic lipid profile

• increased proportion of people reporting poor health

What was the impact of exposure to famine on mid gestation foetuses from the 1944 Dutch famine?

increased obstructive airway disease

What was the impact of exposure to famine on late gestation foetuses from the 1944 Dutch famine (2)?

• decreased glucose tolerance

• improved fertility / women with more offspring and increased twin incidence (societal or a protective mechanism?)

What is the importance of cortisol to a foetus (different roles) (6)?

• reflects nervous system maturation

• stimulates lung growth, development and surfactant production

• cardiac responses (output, pressure and peripheral resistance)

• accumulates glycogen reserves

• stimulus for initiation of own labour

• foetal programming of stress responses = effects on chronic diseases in adulthood