Pregnancy and Birth Flashcards
Gestational trophoblastic disease
Hydatidiform mole
Placental trophoblast proliferation, can be benign or malignant
Negative pregnancy hCG levels
below 5 mIU/mL
Anembryonic pregnancy
Blighted ovum/afetal sac
Gestational sac where fetus hasn’t developed
Fetal demise
Fetus hasn’t survived
Not an emergency
Normal fetal heart rate
120–140 bpm
Threatened miscarriage
Incidence of around 25-30%
Bleeding in first trimester
Subchorionic bleeding –not always bad, bleed can seal on its own
If bleed occurs on opposite side to the fetus it’s less of a worry, but if it occurs on the sam side it can obstruct placental formation
Abnormal gestation sac
Lack of yolk sac and double decidual reaction, therefore lack of embryo
Preeclampsia
Hypertension specific to second half of human pregnancy
3–8% of all pregnancies
Proteinuria
Recurrent miscarriage
3+ miscarriages with the same partner
Usually in a row and usually early in the pregnancies
Often due to issues with placenta formation
Spontaneous miscarriage
Nature’s way of dealing with a non-viable embryo
Essential functions of the placenta
1) Self maintenance/renewal
2) Exchange/transport/transfer
3) Separation of foetus from mother
4) Protection of foetus from maternal functions
5) Protection of foetus from maternal immune system
Placental burrowing
1) Adhesion
2) Lacunar phase starts at day 8
3) Lacunar phase ends at day 12
In the human placenta, the trophoectoderm implants into endometrium (ICM first)
Primitive syncytium digests decidua and eats its way into the endometrium
At day 12 the embryo is fully enclosed in the uterine wall
Real placenta
After day 12, when the placenta is fully enclosed in the uterine wall
Villous period
Real placenta development after day 12
Cytotrophoblasts proliferate and invade the trabeculae which become primary villi
The lacunar system is now called the intervillous space, which is where maternal blood eventually ends up
At about day 14, cells of the extraembryonic mesenchyme invade the primary villi, forming secondary villi
Tertiary villi
18–20 days in, capillaries form in the villi, forming tertiary villi
The vessels in the villi connect to the umbilical vessels carrying blood to and from the foetus
Floating villi
Villi that are suspended in the intervillous space, not in contact with the maternal tissues
Responsible for the exchange and barrier functions of the placenta
Chorion laeve
Placental membrane
Chorion frondosum
Placenta itself
At six weeks, completely surrounds embryo
Villous regression
At the beginning, the placenta is round. To become oval and flat, the more lateral villi and those near the uterine lumen regress to form the chorion leave. The villi at the base of the implantation site form the chorion frondosum.
Anchoring villi
Crucial to placenta function
In a few villi, cytotrophoblasts break through the syncytiotrophoblast. The cytotrophoblasts spread laterally around the implantation site, forming a cytotrophoblast shell which remains in contact with maternal tissue. Columns of cytotrophoblasts continue to stream out of the anchoring villi to invade the decidua and spiral arteries during the first and second trimesters.
Role of placenta formation in regards to spiral arteries
Spiral arteries usually have a layer of smooth muscle in the walls that is tonically active. Invading cytotrophoblasts move down the spiral arteries, replacing the smooth muscle and becoming endovascular trophoblasts. This inhibits muscular activity and is thought to be key in preventing preeclampsia, as this process is not completed in preeclamptic patients.
Endovascular trophoblast plugs
Important to establish placental physical presence so the fetus can tolerate the blood flow
Embryos are designed to live in low oxygen environments so the trophoblast plugs prevent premature perfusion to avoid mechanical and oxidative injury
Breaks down around 10 weeks, full perfusion of placenta should resume by 13 weeks
Not solid –red blood cells can’t pass through but plasma can
Villous
Branch of the placenta
Villous cytotrophoblast
Trophoblast progenitor cell type found mainly in the first trimester underlying the syncytiotrophoblast
Syncytiotrophoblast
Cell that covers entire surface of placenta
Formed by fusion of villous cytotrophoblasts –does not replicate but additional fusion of villous cytotrophoblasts can replace parts
Extravillous cytotrophoblast
Differentiated cells that have migrated out of the villous placenta towards the maternal tissues
Structural changes of the placenta with gestational age
During early pregnancy, stroma of the villi become cellular and vascularised. During the 2nd trimester, villous cytotrophoblast thins down. During the 3rd trimester, villous cytotrophoblast is sparse.
Branching of the villi increases and the size of the placenta increases.
Decidua basalis
The decidua underlying the implantation site
Decidua capsularis
The decidua overlying the implantation site – the part that heals back behind the embryo
Decidua peritalis
The decidua around the remainder of the uterus
Fusion of the decidua capsularis with the decidua peritalis
As gestation progresses, the amniotic cavity enlarges, obliterating the uterine cavity, leading to fusion of the two decidua.
The placental membranes
Amnion
Chorion
Decidua