Pregnancy Flashcards
What does “conceptus” refer to?
Everything resulting from fertilised egg: Baby Placenta Foetal membranes Umbilical cord
In the UK, what gestational age is attempt at revival made if they are born pre-term?
24 weeks
In which trimester is spontaneous loss of pregnancy common?
1st
In the absence of an ICU cot, what is the absolute limit of gestational period for survival of a pre-term baby?
26-27 weeks
With an ICU cot, what is the absolute limit of gestational period for survival of a pre-term baby?
22-23 weeks
Which gestational weeks are considered “term”?
37-41
Summarise the hormonal changes during the first trimester
hCG peaks
Oestrogens, Progesterone + placental lactogen begin to increase in parallel with growing placenta
How do levels of progesterone and oestrogens in pregnancy compare with menstrual cycle levels?
They greatly exceed those in the normal menstrual cycle
Describe the levels of LH and FSH throughout pregnancy
Very low as high levels of Oestrogens + Progesterone suppress the HPG axis
Which hormone must be at very high levels to allow pregnancy to continue? What can low levels or an antagonist cause?
Progesterone
Low levels/ antagonist leads to loss of pregnancy
Which hormone is associated with morning sickness?
hCG
Peaks in 1st trimester
Recall 2 possible mechanisms for the altered immune response in pregnancy
- Endogenous immunosuppressant production at utero-placental interface
Decreasing Th1 responses
Increasing Th2 system - Placental HLA-G expression
Provides immunological signal that shows tissue is human
Recall 3 major maternal changes in the 3rd trimester
- Loosening of pelvic joints
- Weight gain of 10-15kg
- Increased urination frequency
Recall the source of progesterone throughout pregnancy
Till 8 weeks: Corpus luteum, production driven by hCG
Placenta can also produce P, but small size means small contribution
Post 8 weeks: Luteo-placental shift
Recall the source of oestrogens throughout pregnancy
Till 8 weeks: corpus luteum
Following LPS: maternal pregnenolone is converted by foetal andrenals to DHEA-S
Placenta converts DHEA-S to 17-B-oestradiol
Fetal liver converts DHEA-S to precursor, placenta converts to Oestriol
To where does the placenta anchor in the uterus?
Decidua
Describe the development of the placental blood supply during pregnancy
- Cytotrophoblast columnar structure forms + branches into villous sprouts
- At 8 weeks: cytotrophoplast plug breakdown; spiral artery formation
- During 2nd + 3rd trimesters there is increased branching, placental diameter = 5–> 20cm
What is the gestational age limit for a foetal death to be considered “miscarriage”?
23 weeks
How is still birth risk assessed?
Foetal movement on ultrasound
What makes the foetus so vulnerable in the first trimester?
Abnormal chromosomal make-up (excess/ deficient chromosomes)
Incomplete anchorage of placenta (increase in pressure can lead to detachment
Depending on type of gain or loss of chromosomes, what consequences are seen in the infant?
Autosomal loss: inviable
Autosomal gain: Chr.21 Trisomy Down Syndrome
Sex Chr. gain: Viable with variability
Sex Chr. loss: Turners syndrome / inviable
Why is placental anchorage essential for maintaining pregnancy?
Cytotrophoblast plugs break down, so spiral arteries provide main supply of nutrients to the developing placenta + fetus.
If not fully anchored to maternal decidua, the increase in pressure on exposure to the maternal arterial supply can detach the placenta + lead to miscarriage
What is the major risk in the second trimester?
Early delivery due to:
Labour starting before term
Deteriorating maternal or fetal health, such that delivery is required to save life of mother, fetus, or both
Why are infants born before 32 weeks GA at greater risk of stillbirth?
Development of lungs, digestive system, brain + immune system is incomplete
What is the most dangerous process in pregnancy for the mother?
Labour
Remodelling of spiral arteries allows loss of large volumes of blood after delivery.
Only limited by contraction of the uterus after delivery of placenta, which diminishes blood loss strongly- may require induction
Must ensure complete Placenta has been delivered, as it inflexible + will prevent uterine contraction, permitting blood loss through spiral arteries.
What changes does the mother go through/ begin to go through in the first trimester?
Increased breast size Increased basal body temperature Increased nausea + vomiting Increased vaginal mucus production Increased urination frequency Altered appetite Altered brain function Altered emotional state Altered joints Altered hormones Altered immune system
What changes does the mother go through/ begin to go through in the second trimester?
Increased weight
Increased blood volume
Increased blood clotting tendency
Decreased BP
When are the terms conceptus, embryo, foetus and infant used?
Conceptus: everything resulting from the fertilised egg (baby, placenta, fetal membranes, umbilical cord)
Embryo: before it’s clearly human
Fetus: rest of pregnancy
Infant: after delivery
What are the 5 main placental functions?
Separation: of vascular systems
Exchange: of nutrients (maternal to fetal) + waste products (fetal to maternal)
Biosynthesis: Placenta is synthetically very active
Immunoregulation: Interactions between placenta + maternal tissues prevents rejection of conceptus
Connection: strong connections with underlying maternal decidua to last 9 months. Placenta is in contact with maternal arterial blood, so anchorage is essential.
Which is essential for pregnancy survival, uterus or placenta?
Placenta
As ectopic pregnancy (implantation not in uterus) + occasional survival of such pregnancies until delivery, demonstrates uterine lining is not essential
What primary subunits is the placenta composed of? How are these optimised for their function?
Placental villi
Complex branched structure, provides a large SA for exchange
Describe the oxygenation states of vessels in the placental villi
Arterial: de-oxygenated blood; carry blood away from fetal heart to placenta
Venous: oxygenated; returns blood to fetal heart
What is the maternal surface of the placenta composed of? How does variability in shape and size affect placental function?
Cotyledons
Each contains >,1 villi, with larger cotyledons containing more
Variability in shape + size of cotyledons doesn’t affect function
Describe the composition of the conceptus 9 days post-fertilisation
Outer layer: Syncytiotrophoblasts (contain fluid-filled lacunae)
Layer of cytotrophoblasts (proliferates adjacent to embryo: this is where the placenta will develop)
Describe placental development post-implantation into maternal decidualising endometrium
Cytotrophoblasts proliferate into surrounding syncytium; as fingerlike projections, which then undergo branching (villous sprouts).
At the centre of each villus are mesenchymal cells, from which the villus vascular system develops.
Branching continues throughout pregnancy, giving rise to complex branched villi
How does number of cytotrophoblasts differ at term? Why?
There are fewer
Allows a closer apposition between the syncytium + placental capillaries
Maximises efficacy of nutrient transfer into fetal blood, + enhances fetal growth in later pregnancy
What happens to decidual glands during the 1st trimester? What is their function?
Decidual glands hypertrophy
Provide nutrients for placenta + baby
What isolates the conceptus from maternal blood by 4 weeks post fertilisation? For how long does this remain?
Proliferating cytotrophoblasts, form a shell around conceptus
Shell remains till 8 weeks post-fertilisation, with spiral arteries blocked by cytotrophoblast plugs
What allows spiral arteries to become the main nutrient supply to the placenta and foetus? In what distribution does this occur?
Breakdown of cytotrophoblast plugs (periphery to centre of placenta)
How does the diameter of the placenta change? What is this due to?
5cm to 20cm
Growth due to increased size + branching of villi
What happens during the remodelling process of spiral arteries by cytotrophoblast? When does it begin and end?
Loss of vascular endothelium + smooth muscle
Replacement by cytotrophoblast
1st trimester to 16 weeks GA
What is the purpose of spiral artery remodelling?
Converts narrow, vasoactive spiral arteries, to wide bore vessels that can transport large volumes of maternal blood to placenta to provide sufficient nutrients.
Blood flow remains high as they can’t respond to vasoconstrictors
What are the effects of the neuronal system on the placenta?
Placenta has no nervous system, thus is not regulated by NS in any way
What regulates growth of the placenta?
Placenta regulates its own growth through autocrine mechanisms
Maternal decidua has a modulatory role to prevent excess growth
How is pregnancy dated by obs-gynae terminology?
Pregnancy is counted from 1st day of last menstrual period, with other events dated from this time.
How is pregnancy dated by embryologic terminology?
Pregnancy counted from fertilisation
What is a miscarriage?
Delivery before viability limit of a non-viable infant
What is a stillbirth?
Death of an infant within the uterus, so it’s delivered with no signs of life
Can be a complication of pregnancy or labour
Can occur at any GA
What are the 2 preferred methods of assessing foetal wellbeing?
Ultrasound
Fetal blood flow (doppler ultrasound)
