Fetal Abnormalities III: Placental Causes Flashcards
What’s the mech for how an error in placental development is thought to cause miscarriage?
- Trophoblasts do not adequately invade the spiral arterioles
- Environment remains perfused with blood; no stage of hypoxic development
- Increased oxidative stress/shear stress leads to atrophy of placental villi
What is the official definition of pre-eclampsia
- Onset of hypertension >20wks (stillborn window)
- Plus at least one of: proteinuria, maternal organ dysfunction, uroplacental dysfunction
Preeclampsia prevention
- Aspirin in first 16 weeks is effective preventative. After that, no.
- Calcium supplementation (if not met by diet)
- Magnesium sulphate
How is the balance between PIGF and sFLT1 changed in pre-eclampsia? Link this to the pathophys
- PIGF is an angiogenic placental growth factor
- sFLT1 is anti-angiogenic (it sequesters angiogenic growth factors)
- In response to increased shear stress and hypoxia from improper vascular remodelling, the placenta produces more sFLT1, thus leading to reduced angiogenesis and further placental hypoxia.
With reference to the placenta, why might twins/higher order pregnancies be at higher risk of pre-term birth/lower birth weight
Same amount of placenta, more competition.
The most common cause of fetal macrosomia is…
Poorly controlled diabetes in the mother
How do we define a drop in fetal growth velocity (as opposed to just a small baby)?
A drop in growth trajectory of >=50 percentiles (or crossing 2 or more lines on the graph)
What metrics do we track to measure fetal growth?
- Head circumference
- Abdominal circumference
- Femur length
How do we determine uteroplacental function/placental blood flow?
Umbilical artery ultrasound doppler study
Pulsatility index is a measure of…
Resistance to blood flow
True or false: blood flows to the placenta in systole, and away from it in diastole
- False
- It always flows towards the placenta
(Think about it: there’s dedicated venous drainage)
If our umbilical artery doppler is abnormal, which scan comes next? How do we interpret the pulsality index?
- Next scan is fetal MCA scan
- If resistance (pulsality index) is low, this indicates hypoxia of the whole fetus, since the body is shunting blood to critical areas such as the brain (often at the expense of other organs)
If umbilical and MCA ultrasounds on a fetus are abnormal, what’s the next scan we consider? How do we interpret it?
- Next is ductus venosus scan
- If pulsitality index is low, this means it’s dilated, which is an indicator if increased cardiac output (often in response to hypoxia)
An ultrasound shows a placenta obstructing the cervix. Why is this important? What is it called?
- Because the mother will likely need a C-section
- Called placenta praevia
