Implantation, Placentation + hormones changes in pregnancy Flashcards
What do we need for plantation to occur?
A fully developed blastocyst - Fully expanded - Hatched out from the zona pellucida A receptive endometrium - thickened endometrial lining Expression of embryo receptivity markers
Blastocyst
Blastocyst is made up of 2 cell lineages – Trophoblast (Purple - forms the placenta) and Embryoblast or inner cell mass (Green - forms the foetus).
Also present inside the blastocyst is a fluid-filled cavity known as the Blastocoel.
The embryoblast is concentrated at the ‘embryonic pole’ while the opposite pole (where trophoblast cells are concentrated) is known as the ‘abembryonic pole’
The placenta
- Around day 17, foetal mesoderm cells start to form blood vessels within the villi – a basic network of arteries, veins and capillaries. Capillaries connect with blood vessels in the umbilical cord (formed around week 5).
- Villi grows larger in size, develops into the Chorionic Frondosum.
- At this point, endothelial cell wall and Syncytiotrophoblast (villi) lining separate maternal and foetal red blood cells.
On ultrasound, chorionic cavity shows up as a large dark space. Used to identify a pregnancy even before a foetus can be seen.
The placenta – maternal – foetal exchange
The placenta is typically formed in the upper uterus.
Umbilical cord normally contains two arteries and one vein.
The placenta functions
- Provision of maternal O2, CHO, fats, amino acids, vitamins, minerals, antibodies.
- Metabolism e.g. synthesis of glycogen.
- Barrier e.g. bacteria, viruses, drugs etc.
- Removal of foetal waste products e.g. CO2, urea, NH4, minerals.
- Endocrine secretion e.g. hCG, oestrogens, progesterone, HPL, cortisol.
Why is the placenta good at it’s job?
• Huge maternal uterine blood supply – low pressure.
• Huge surface area in contact with maternal blood.
• Huge reserve in function.
The placenta is typically formed in the upper uterus. Barrier is formed by the cells of the villi.
Pre eclampsia
- 3-4% of pregnancies.
- ≥20 weeks gestation (up to 6 weeks after delivery).
- Results in placental insufficiency – inadequate maternal blood flow to the placenta during pregnancy.
- Causes new onset maternal hypertension and proteinuria.
- Symptoms range from mild to life-threatening.
Pre eclampsia risk factors
• First pregnancy • Multiple gestation • Maternal age >35yo • Hypertension • Diabetes • Obesity • Family history of pre-eclampsia Pre-eclampsia + seizures = Eclampsia
Placental insufficiency
– inadequate maternal blood flow to the placenta during pregnancy. This in turn compromises the transfer of necessary nutrients to support the development of the foetus.
Pre-eclampsia usually occurs after around 20 weeks gestation. Could still develop after delivery – up to 6 weeks after delivery
Reduced blood flow to kidney
Then Glomerular damage > proteinuria
Pre eclampsia cause
- Primary cause is still unclear.
* Characterised by the narrowing of the maternal spiral arteries supplying blood to the placenta.
Placental abruption
Premature separation of all or part of the placenta - Symptoms include vaginal bleeding and pain in the back and abdomen
Placental abruption - Risk factors
Blunt force trauma e.g. car crash, fall Smoking & recreational drug use - risk of vasoconstriction and increased blood pressure Multiple gestation Maternal age >35 yo Previous placental abruption
Placental abruption - Complications - Foetal
- Intrauterine hypoxia and asphyxia
* Premature birth
Placenta Previa
- Placenta implants in lower uterus, fully or partially covering the internal cervical os.
- Associated with increased chances of pre-term birth and foetal hypoxia.
Placenta Previa - Risk factors
- Previous caesarean delivery
- Previous uterine/endometrial surgery
- Uterine fibroids
- Previous placenta previa
- Smoking & recreational drug use
- Multiple gestation
- Maternal age >35yo
