Flashcards in Maternal-Foetal and Placental Physiology Deck (40):
What is the primary metabolic substrate for placental metabolism?
Glucose is the single primary metabolic substrate for placental metabolism
How is glucose transferred across the placenta?
How are amino acids transferred across the placenta?
Active transport: higher concentration in foetus than in the mother
What does the placenta produce?
Oestrogen, progesterone, hCG and hPL
Where does oxygenation of foetal blood occur?
Placenta, NOT lungs
What is the pathway of oxygen blood to the foetus?
Oxygenated blood carried from placenta to the foetus through the umbilical vein, which enters the portal system of the foetus and branches to left lobe of liver. another branch joins blood flow from portal vein to R lobe of liver.
What does the umbilical vein become?
Origin of the ductus venosus
What happens to blood passing through the foetal right ventricle?
-Less than 10% to pulmonary vasculature
-Majority shunted through ductus arteriosus and descending aorta
How does umbilical blood flow relate to foetal size?
Umbilical blood flow represents 40% of combined output of both foetal ventricles. Proportional to foetal growth in last half of pregnancy (~300mL/mg per minute).
i.e. relatively constant, normalised to foetal weight.
What is foetal Hb comprised of?
HbF = a2, y2
What is the key physiologic difference between HbA and HbF?
At any given oxygen tension, HbF has higher oxygen affinity and oxygen saturation than HbA.
Describe O2 / CO2 exchange between mother and foetus?
-Maternal respiratory alkalosis facilitates transfer of CO2 from foetus
-Loss of CO2 from foetus causes rise in foetal blood pH, shifting foetal oxygen dissociation curve to left and increasing O2 binding affinity.
Describe the foetal renal system
-Functional in 2nd T
-Produces dilute, hypotonic urine
-Urine production varies with size (400 - 1200mL / day)
-Primary source of amniotic fluid by middle of 2nd T
Describe the foetal liver
-Slow to mature
-Capacity for glycogen synthesis and bilirubin conjugation increases with gestational age (so bilirubin primarily eliminated through placenta)
-Coag factor synthesis deficient, may be attenuated in newborn due to VitK deficiency
How does the foetal thryoid rely on the mother?
-Mother only primary source of T3/T4 prior to 24 - 28 weeks
-Placenta does not transport TSH
-Gland develops without direct influence from mother, functional by end of first trimester
What does testicular differentiation rely on?
Presence of H-Y antigen and Y chromosome
Why does the mother not reject the antigenically dissimilar foetus?
Appears to be due to placenta
-maintaining separation of foetal and maternal compartments, keeping foetus from contact with maternal immune system
-production of oestrogen, progesterone, hCG, hPL locally decreasing immunity
-producing blocking and masking Abs
What is the major foetal immunoglobulin?
Only maternal IgG can cross the placenta hence maternal IgG major proportion of foetal immunoglobulin
What is the incidence of monozygotic twinning?
One in 250
What are the different influences on monozygotic v dyzygotic twinning?
-Mono: not affected by race, heredity, age, parity or infertility agents.
-Dizygotic: affected by all agents
When will MZ twins be dichorionic and diamniotic?
if there is separation of the blastocyst within the first 72h
What will result if division of the embryo occurs between days 4 - 8?
When do conjoined twins occur?
MZ twins with late division after formation of the embryonic disk
What happens to deoxygenated foetal blood?
Returned to placenta through the umbilical branches of the two hypogastric arteries. Umbilical arteries exit ado wall at umbilicus and continue through cord to placenta.
Which condition increases incidence of SUA?
SUA increased in diabetic mothers
What does SUA increase?
Risk of foetal malformations (up to 18%) usually involving cardiac and renal systems.
Woman with appearance of spidery veins on face, arms, chest during later pregnancy. Mx?
-vascular spiders / angiomas common findings during pregnancy
- due to hyper oestrogenism
-no further workup / Rx; will resolve after delivery
Why should pregnant women take iron in a multivitamin?
Even if not currently anaemic, amount of iron in diet and that can be mobilised insufficient to meet demands of pregnancy.
-pregnant woman with normal haematocrit at start of pregnancy will develop iron deficiency in latter part of gestation
When do iron requirements increase significantly during pregnancy?
Second half of pregnancy
Will the foetus suffer if maternal iron supplementation does not occur during pregnancy?
No. Placenta will transport required iron at expense of mother.
Why is haematocrit not usually used as a parameter to determine when maternal iron supplementation is required?
Usually falls during pregnancy due to haematocrit expansion; therefore not reliable indicator of when to commence supplementation
Normal changes to ureters / kidneys during pregnancy?
Bilateral mild hydronephrosis and hydroureter. Do not require additional workup.
Why does hydronephrosis / hydroureter develop during pregnancy?
When gravid uterus rises out of the pelvis after 12 weeks gestation it presses on ureters at pelvic brim. Usually more pronounced on RHS. Hormonal effect of progesterone probably also contributes.
Why do pregnant woman often have trace glucose in urine?
Increase in GFR and decreased tubular reabsorption of glucose
What is placenta accrete?
When trophoblastic tissue invades superficial lining of the uterus. Placenta abnormally adherent and cannot be separated from uterine wall.
What is a succenturiate placenta?
One or more smaller accessory lobes located in the membrane at a distance from the main placenta. Retained succenturiate lobe may cause uterine atony andPPH
What are common triggers for haemorrhage in placenta praevia?
Painless haemorrhage without warning. Often occurs:
-tearing of placental attachments during formation of the LUS in T3
-Cervical dilation during term or preterm labaour
What are the risks for placenta praevia?
What is fenestrated placenta?
Rare. Central portion of placenta is missing.