9.15 High Risk Pregnancies Flashcards
What does the Rh negativity imply?
Absence of D-antigen
What are the most common antibodies?
- AB
- O
To what antigens do antibodies have the potential to cause haemolytic disease of the fetus / newborn?
- anti-Rh(D)
- anti-c
- anti-E
- anti-Kell
*Anti-Fa (Duffy) & Kidd rarely causes significant problems)
What happen when the mother is negative for offending antigen (Rh negative) and pregnant with fetus positive for offending antigen (Rh positive)?
- Maternal exposure to fetal red cell antigen –> weak maternal immune response –> IgM production (does not cross placenta into fetal circulation) - usually first pregnancy not affected.
- Subsequent maternal exposure to fetal red cell antigen –> memory B-cells produce IgG antibodies –> actively transported across the placenta –> IgG binds to fetal red blood cells –> haemolysis, cytolysis and phagocytosis of fetal red blood cells –> fetal anaemia –> untreated –> hydrops fetalis
Events during which Rh sensitization / significant feto-maternal haemorrhage can occur:
1st trimester
- Miscarriages / Ectopic pregnancy
- CVS (Chorionic Villus Sampling) -> genetic testing
2nd Trimester
- Miscarriage
- Amniocentesis / Cordocentesis. -> testing
3rd Trimester
- External cephalic version (procedure to turn baby from breech position to head-down position)
- Antepartum haemorrhage
- Delivery
- Manual removal of placenta
- Abdominal trauma
Complications for twin pregnancies irrespective of chorionicity and amnionicity?
Maternal:
- Exaggerated pregnancy signs and symptoms (eg. Hyperemesis)
- hypertensive disorders
- gestational diabetes mellitus
- anaemia
- caesarean section
- post-partum haemorrhage
Fetal:
- miscarriage
- preterm delivery
- fetal growth restriction
- anomalies
Dizygotic twins vs. Monozygotic twins
Dizygotic twins
- non-indentical twins arising from two sperms fertilizing two ova
- dichorionic
Monozygotic twins
- identical twins arising from one sperm fertilizing one ovum
- may be dichorionic or monochorionic
- depends on the timing of cleavage.
Vascular connections of monochorionic twins and risks thereof
- they share a placenta
- have vascular connections that are shared = anastomoses
Placental anastomoses risks
- Twin to twin transfusion syndrome
- Twin anaemia-polycythaemia sequence
- Twin reversed arterial perfusion syndrome
What does later division of monozygotic twins lead to and the risks thereof
Monamniotic twins - sharing of one amniotic cavity
Risks:
- ⬆️ risk of morbidity and mortality most related to cord entanglement
- Even later division results in conjoined twins with the highest morbidity and mortality largely related to the organ(s) that are shared
Examples of pre-existing cardiac pathologies
- cardiomyopathy
- coronary artery disease
- valvular heart disease
What physiological & hormonal changes occur with pregnancy that may exacerbate pre-existing cardiac conditions?
Cardiac output
- Estimates for increases in a cardiac output range from 20 to 50%
- accounted for by an increased stroke volume of about 25% in the first trimester
- Pregnant women cardiomyopathy may not adequately compensate for this stress
- may develop complications such as pulmonary oedema.
Heart rate:
- Along with an increase in stroke volume, there is an increase in heart rate of approximately 15 to 30% in the first trimester
- also contributes to an increase in cardiac output.
Systemic vascular resistance:
- decreases during pregnancy
- Estimates are that this change may be as much as 30%.
Blood pressure:
- Blood pressure slightly decreases early in pregnancy
- Overall, more commonly, diastolic blood pressure decreases predominate over-systolic blood pressure early in pregnancy
- value normalizes or even increases by the end of pregnancy.
Increase in volume of pregnancy
- leads to enlargement of the atria and ventricles
- may be poorly tolerated in hearts that already have pathological changes
