Pregnancy Flashcards
What stage in weeks, is each trimester?
1st trimester is 0-13 weeks; 2nd trimester is 14-26 weeks; 3rd trimester is 27-39 weeks.
What week is the baby viable?
26/27 weeks (third trimester).
What are the features of the first trimester of normal human pregnancy?
□ Spontaneous loss of the pregnancy during the first trimester is relatively common (miscarriage). □ Mother experiences altered brain function – from very high exposure to steroids, particularly progesterone. □ Altered emotional state. □ Altered appetite (quantity and quality) from the baby pressing on the GI tract for the first time. Altered appetite can also arise from ‘morning sickness’ which occurs in this trimester. □ From this trimester and onwards, there is altered immune system (to allow pregnancy to continue with the baby having an entirely different genetic composition).
What are the features of the second trimester of normal human pregnancy?
□ Is the absolute limit of infant survival, in the absence of modern neonatal intensive care. □ There is the largest increase in blood volume in this trimester (and in 3rd trimester). □ There is increased clotting tendency. □ Decrease in blood pressure – increases risk of fainting. □ Altered fluid balance – kidneys are working harder; mother is drinking more. Associated with increased blood volume.
What are the features of the third trimester of normal human pregnancy?
□ Sees the largest increase in the weight of the mother. When the baby grows the fastest and most. □ Sees the largest alteration to joints: joints become more flexible, the vertebral curvature changes to accommodate for the change in weight distribution. The pelvis also alters its structure and breaks to allow for delivery. □ By the third trimester, the greatly enlarged uterus will be exerting pressure on the bladder, decreasing the maximum size and volume of urine it can contain, so the mother will pass smaller volumes of urine more frequently.
What happens to the immune system during pregnancy? (x2 systems) !!!
□ Pregnancy requires the survival of a ‘non-self’ entity for a period of 9 months, with no signs of a rejection reaction in normal pregnancy. Two major systems seem to be involved in the immunological aspects of human pregnancy. □ Firstly, several factors that can suppress the maternal immune system are produced at the utero-placental interface. These co-operate to modify the maternal immune system, including decreasing the Th1 responses and increasing the Th2 system. □ The second major system is that the placenta expresses some very unusual Human Leukocyte Antigens (HLA) on the surface that is in contact with maternal tissues. Unlike the HLA with which we are most familiar (HLA-A, HLA-B, HLA-D), which are very polymorphic and exist in millions of potential variants. the placental HLA (HLA-G) is almost invariant – there are just 5 GENETIC VARIANTS. It is believed that HLA-G provides an immunological signal that shows that the tissue is human. In addition, HLA-G can suppress the activity of some leukocytes and can down-regulate the maternal immune system within the uterus.
What happens to temperature throughout pregnancy?
Basal body temperature increases by ~0.5°C in the second half of the menstrual cycle after ovulation from progesterone levels. As the fetus increases in size, it contributes to maternal temperature, and normal maternal temperatures may exceed 38°C.
What happens to mucous production from the vagina throughout pregnancy?
A common and normal change in pregnancy, clear mucus is produced throughout most of pregnancy.
What is hyperemesis gravidarum?
The most severe version of morning sickness but uncommon.
What is term?
Describes the 39-40 weeks of the expected timing of delivery. While this is normally stated as 280 days since the beginning of the last menstrual period (40 weeks), as a medical terminology, ‘term’ covers gestational ages from 37 – 41 weeks of gestation, with deliveries either side of these limits being ‘preterm’ or ‘post-term’ respectively.
What happens to the levels of four hormones in the mother during pregnancy?
□ In early pregnancy, the hormone levels are similar to that experienced in the menstrual cycle. The small ‘bump’ that can be observed in progesterone and oestrogen levels in the bottom left corner looks small only because the hormonal changes in pregnancy are HUGE in comparison.
□ HCG is released from the placenta and peaks during the first trimester. It stimulates the corpus luteum to continue producing progesterone and oestrogen to maintain the pregnancy. It is still present in the latter stages of pregnancy, but at relatively lower levels.
□ Oestrogen and progesterone increase slowly and dramatically and reach their peaks in the third trimester.
□ Placental lactogen also increases at similar rates. This hormone modifies the metabolic state of the mother during pregnancy to facilitate the energy supply of the foetus.
□ The increased levels of progesterone, oestrogens and placental lactogen parallel with the increased size of the placenta.
□ The high levels of progesterone and oestrogen suppress LH and FSH levels so that the ovarian cycle does not occur.
Where is progesterone produced throughout pregnancy? (x2)
From 0-8 weeks, progesterone is produced in the corpus luteum, and sustained by high levels of hCG. The placenta also produces progesterone, but in the earliest weeks of pregnancy, its small size means that its contribution is very little. Increasing placental size means that it contributes increasingly to the net levels of progesterone in the maternal circulation, and by 10 weeks, the placenta is the source of all progesterone. From about 6 weeks of gestational age, the corpus luteum gradually produces less progesterone (despite the very high hCG levels), and by about 9 weeks it has ceased to make steroids. This change in the source of progesterone to sustain pregnancy is the ‘LUTEO-PLACENTAL SHIFT’.
Where is oestrogen produced throughout pregnancy?
In the early weeks, corpus luteum produces oestrogen (mainly 17-beta-oestradiol). Once the luteo-placental shift has completed, oestrogens are produced through a complex interaction between maternal adrenals, fetal adrenals and liver, and the placenta.
How are oestrogens produced during pregnancy (after corpus luteum has packed up)?
□ The human placenta does not express the enzyme that converts pregnenolone to androgens, so this part of biosynthesis takes place in the fetal and maternal adrenals.
□ The mother produces DHEA-S from cholesterol in their own adrenals (Cholesterol –> pregnenolone –> DHEA-S). DHEA-S is converted into estrone and then 17B-oestradiol in the placenta.
□ The foetus produces DHEA-S in their adrenals which are well-developed even in the first trimester. It also receives substrates to make DHEA-S from the placenta. DHEA-S is then brought to the placenta and converted into 17B-oestradiol the same way that occurs to maternal DHEA-S.
□ DHEA-S can also be converted into 16alpha-OH-DHEA-S in the foetal liver, and converted into estriol in the placenta.
From what day is pregnancy counted by embryologists? How does this differ from the convention?
Conventionally, the first day of the last menstrual period (LMP) is considered the point at which the timing of the pregnancy begins. Developmental embryologists start from the point of fertilisation (conception), which is about two weeks after LMP.
What is a blastocyst?
Comprises of a bilaminar disc that has developed from the egg and contains two layers of cells – epiblasts which will give rise to the ultimate embryo proper, and hypoblasts which contribute to extraembryonic membranes.
When is a baby most susceptible to developmental issues?
In the first trimester, as this is when most organs are developing – particularly in the first 8 weeks. See photo.
What is the basic placental structure? !!!
□ The maternal surface of a normal placenta is arranged into COTYLEDON – these are subunits of the maternal placenta which transmit foetal blood and allow exchange of oxygen and nutrients with the maternal blood.
□ Each cotyledon contains one or more villi. The placental villus is the primary subunit have large, branched structures. These provide a large surface area for exchange between the maternal and foetal vascular systems.
□ Within each villus there is a complex blood supply, including arterial and venous vessels, connected to smaller capillaries in the terminal portions of each villus. Note that the arterial system contains de-oxygenated blood, and the venous blood is oxygenated – because the placenta has a parallel function to the lungs for the fetus during pregnancy.
□ The two circulations do not meet each other.
What is the process of placental development?
□ Starts as a single layer of cells (hypoblasts) in the blastocyst.
□ They proliferate and differentiate into SYNCYTIOTROPHOBLASTS (these form the outer layer and form the SYNCTIUM) and CYTOTROPHOBLASTS. The cytotrophoblasts are the cells from which the placenta arises.
□ Following implantation, the cytotrophoblasts proliferate into the SYNCYTIUM. The cytotrophoblasts form columnar structures (red), which then undergo branching (producing villous sprouts; blue).
□ At the centre of each villus are mesenchymal cells.
□ Branching complexity and surface area increase throughout pregnancy.
How does contact between the placenta and maternal blood system vary throughout pregnancy? (x2)
□ At 8 weeks gestational age, the provision of blood from mother to the foetal circulation at the placenta is through structures called spiral arteries which reside in the endometrium of the uterus.
□ (1) These are remodelled by cytotrophoblasts which invade the walls, removing their vascular endothelial cells and smooth muscle.
□ Babies grow dramatically in the second and third trimesters. This spiral artery remodelling is therefore important, because it prevents the maternal arteries from constricting (by removing VSMCs), thus maintaining high level of blood flow to the placenta to facilitate rapid foetal growth.
□ (2) In the first trimester, a cytotrophoblast shell (shown in red) greats a wall which limits blood supply to the embryo – they essentially BLOCK spiral arteries. In cytotrophoblast remodelling (around 10 weeks), these shells breakdown, so spiral arteries can become the main supply of nutrients to the developing foetus and placenta – facilitating foetal growth in later pregnancy.
