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8) Pregnancy Flashcards

1
Q

On what day does the blastocyst implant into the endometrium of the uterine cavity?

A

Day 6 (after fertilisation)

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2
Q

What does further embedding of the blastocyst into the endometrium rely on?

A

Invasive property of trophoblast cells
Outer layer of syncitiotrophoblast
Underlying cytotrophoblast

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3
Q

By what day is the blastocyst fully embedded within the endometrium?

A

10th day after fertilisation

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4
Q

Implantation is interstitial, what does this mean?

A

Uterine epithelium is breached & conceptus implants within stroma

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5
Q

The placenta is haemomonochorial. What does this mean?

A

One layer of trophoblast separates maternal blood from foetal capillary wall

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6
Q

What are the aims of implantation?

A

Establish the basic unit of exchange (Primary, secondary & tertiary villi)
Anchor the placenta
Establish maternal blood flow within the placenta

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7
Q

What are the differences between primary, secondary & tertiary villi in the conceptus?

A

Primary villi - early, finger-like projections of trophoblast (day 13)
Secondary villi - Invasion of mesenchyme into core (day 15-16)
Tertiary villi - Invasion of mesenchyme core by foetal vessels (day 23)

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8
Q

How is the endometrium of the uterus prepared for implantation?

A

Decidualisation

Remodelling of spiral arteries

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9
Q

What is decidualisation (of the uterine endometrium)?

A

Pre-decidual cells
Decidual reaction provides balancing force for the invasive force of the trophoblast
Stimulated by progesterone
Without balancing force complications e.g. haemorrhage

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10
Q

How are the spiral arteries of the endometrium remodelled in preparation for implantation?

A

Creation of low resistance vascular bed

Maintains high flow required to meet foetal demand particularly late in gestation

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11
Q

What implantation defects can occur?

A 
Ectopic pregnancy (most commonly F. tube)
Placenta praevia
Incomplete invasion (placental insufficiency, pre-eclampsia)
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12
Q

What is placenta praevia?

A

Implantation in the lower uterine segment
Can cause haemorrhage in pregnancy
Requires C-section delivery

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13
Q

Describe the structure of the placenta by the beginning of the 4th month

A
  1. Foetal portion
    Formed by chorion frondsum, bordered by chorionic plate
  2. Maternal portion
    Formed by the decidua basalis
    The decidual plate is most intimately incorporated into placenta
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14
Q

In the placenta, what lies between the chorionic & decidual plates?

A

Intervillous spaces

Filled with maternal blood

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15
Q

During the 4th & 5th months, what happens to the placenta?

A

Decidua form decidual septa
Septa project into intervillous spaces but don’t reach chorionic plate
Septa divide placenta into compartments - Cotyledons

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16
Q

Throughout pregnancy how much of the uterus does the placenta cover?

A

15-30% of the internal surface of the uterus

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17
Q

Describe the first trimester placenta

A

Placenta established
Placental ‘barrier’ to diffusion still relatively thick
Complete cytotrophoblast layer beneath syncytiotrophoblast

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18
Q

Describe the placenta at term

A

Surface area for gas exchange dramatically increased
Placental ‘barrier’ now thin
Cytotrophoblast layer beneath syncytiotrophoblast lost

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19
Q

Describe the arrangement of foetal blood vessels within the placenta

A

Umbilical arteries & veins project into tertiary villi
Tertiary villi bathed in oxygenated maternal blood
2 Umbilical arteries
- Deoxygenated blood foetus > placenta
1 umbilical vein
- Oxygenated blood placenta > foetus

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20
Q

How do cotyledons receive their blood supply?

A

80-100 spiral arteries pierce decidual plate
Pressure forces oxygenated blood deep into intervillous spaces, bathes small villi
As pressure decreases, blood flows back from chorionic plate towards decidua, enters endometrial veins

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21
Q

What factors influence the passive diffusion of substances across the placenta?

A

Concentration gradient
Barrier to diffusion (placental membrane thins as foetal demands increase)
Diffusion distance (haemomonochorial)

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22
Q

Which substances are transported across the placenta?

A 
- Simple diffusion
water, electrolytes, urea & uric acid gases (flow-limited)
 - Facilitated diffusion
Glucose
 - Active transport
Amino acids, iron, vitamins
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23
Q

What are teratogens?

A

Substances or environmental agents which cause the development of abnormal cell masses during foetal growth, resulting in physical defects in the foetus

24
Q

Name some common teratogens

A 
Thalidomide
Alcohol
Therapeutic drugs
Drugs of abuse
Maternal smoking
25
Which pathogens are able to cross the placenta?
``` Varicella zoster Cytomegalovirus Treponema pallidum Toxoplasma gondii Rubella ```
26
What hormones does the placenta produce?
``` Protein hormones - Human chorionic gonadotrophin (hCG) - Human chorionic somatomammotrophin (hCS) - Human chorionic thyrotrophin - Human chorionic corticotrophin Steroids - Progesterone - Oestrogen ```
27
What is hCG?
Human chorionic gonadotrophin Produced during first 2 months of pregnancy Supports the secretory function of the CL Produced by syncytiotrophoblast so pregnancy specific
28
What is the function of human chorionic somatomammotrophin?
Influences maternal metabolism | Increases availability of glucose to foetus
29
During pregnancy where is progesterone produced?
Corpus luteum up to week 11 Placenta takes over production Influences maternal metabolism, increased appetite
30
Apart from protein & steroid hormones, what else does the placenta synthesise?
Glycogen Cholesterol Fatty acids
31
Describe how pregnancy tests work
Tests hCG hCG produced in first 2 months of pregnancy Produced by syncytiotrophoblast so pregnancy specific Excreted in maternal urine
32
What type of immunity can the placenta provide the neonate with?
Passive immunity Foetal immunoglobulins consist almost entirely of maternal immunoglobulin (IgG) Mother > Foetus around week 14 Receptor mediated pinocytosis Eventually foetal plasma IgG exceeds maternal
33
How may a newborn contract a haemolytic disease from its mother?
Rhesus blood group incompatibility Mother previously sensitised to rhesus antigen (previous pregnancy) IgG against rhesus crosses placenta & attacks foetal RBCs Now uncommon due to prophylaxis
34
What prophylactic treatment is there for haemolytic disease of the newborn?
Rhesus -ve mothers pregnant with rhesus +ve foetus given specific IgG throughout pregnancy (anti-D) Prevent sensitisation if exposed to antigen (IgG binds to antigen before mother's immune system can mount a response)
35
Physiological changes take place in which main systems of the body during pregnancy?
``` CVS Urinary Respiratory GI Immune Metabolic changes - carbohydrate, thyroid hormones ```
36
What maternal physiological changes take place in the Cardiovascular system during pregnancy?
``` CO increases 40% SV increases 35% HR increases 15% Blood volume increases Systemic vascular resistance decrease 25-30% ```
37
What happens to maternal BP during pregnancy?
Hypotension T1 &T2 (progesterone effects on systemic vascular resistance) Returns to normal T3 (aortocaval compression by gravid uterus) Systolic BP never normally increased in pregnancy
38
What maternal physiological changes take place in the Urinary system during pregnancy?
Renal plasma flow (60-80%) & GFR (55%) increase Creatinine clearance & protein excretion increase Plasma urea, uric acid, bicarbonate & creatinine decrease
39
Urinary stasis can occur during pregnancy. How?
Progesterone relaxes the smooth muscle in walls of ureters | Can cause stastis, hydroureter, UTIs, pyelonephritis - can induce pre-term labour
40
What maternal physiological changes take place in the Respiratory system during pregnancy?
Diaphragm displaced A-P & transverse diameters of thorax increase O2 consumption increases (20%) Resting minute ventilation & Tidal volume increase Respiratory rate, VC & FEV1 unchanged Functional residual capacity decreased (T3)
41
What happens to the acid-base balance of the mother during pregnancy?
Physiological hyperventilation driven by progesterone Allows mother to blow off extra CO2 produced by foetus Respiratory Alkalosis Kidneys compensate, produce & reabsorb less HCO3-
42
What maternal changes take place with carbohydrate metabolism during the first half of pregnancy?
Foetal supply of glucose & a.a. favoured Fat laid down in 1st half of pregnancy helps meet later foetal demands Progesterone stimulates appetite & diverts glucose into fat synthesis Oestrogen stimulates prolactin release, generates maternal resistance to insulin Maternal glucose usage declines, gluconeogenesis increases, maximises availability of glucose to foetus
43
What maternal changes take place with carbohydrate metabolism during the second half of pregnancy?
Mother's energy needs met by metabolising peripheral fatty acids Placental transport of glucose (facilitated diffusion) Increased maternal peripheral insulin resistance (switch to gluconeogenesis & other fuels) Achieved by human placental lactogen (prolactin, oestrogen/progesterone & cortisol) Decreased fasting blood glucose Increase in post-meal (post-prandial) blood glucose
44
What is gestational diabetes?
Carbohydrate intolerance first recognised in pregnancy and does not persist after delivery Oral glucose tolerance test required Pancreas unable to respond to metabolic demand of pregnancy, blood glucose increases When demands removed, pancreas can respond adequately again
45
What risks are associated with poor control of gestational diabetes?
Macrosomic foetus Stillbirth Increased risk of congenital heart defects
46
How does the pancreas usually cope with the increased demand for insulin during pregnancy?
Basal & stimulated insulin normally increases as pregnancy proceeds Beta-cell hyperplasia & hypertrophy Increased rate of insulin synthesis in the beta-cells
47
What maternal changes take place regarding lipid metabolism during pregnancy?
Increase in lipolysis from T2 Increase in plasma [free fatty acids] on fasting (fatty acids for mum, glucose for foetus) Increased utilisation of free fatty acids increases risk of ketoacidosis (may combine with compensated resp alkalosis = very bad!)
48
What maternal changes take place regarding the thyroid during pregnancy?
Thyroid binding globulin production increased T3 & T4 increased Free T4 in normal range due to increased binding globulin
49
What effect does hCG have on the thyroid during pregnancy?
Direct effect Stimulates T3 & T4 production TSH can be decreased in normal pregnancies due to -ve feedback from T3 & T4 produced due to hCG secretion
50
What maternal physiological changes take place in the Gastrointestinal system during pregnancy?
Anatomical - alterations in position of viscera (appendix moves RLQ > RUQ as uterus enlarges) Physiological - Smooth muscle relaxation (progesterone), GI delayed emptying, Biliary tract stasis, Increased risk of pancreatitis
51
Pregnancy is a pro-thrombotic state. What consequences does this have?
High amount of fibrin deposition at site of implantation - Increased fibrinogen & clotting factors - Reduced fibrinolysis Stasis, venodilation Results in thromboembolic disease in pregnancy - Cannot give warfarin (teratogenic)
52
What type of anaemia can occur during pregnancy?
Physiological anaemia - not true anaemia, mis-match between volume & haemocrit Plasma volume increases RBC mass also increases, not to same degree Anaemia due to Fe and folate deficiency can also occur
53
What maternal physiological changes take place in the Immune system during pregnancy?
Foetus = allograft (genetically different to mother) Non-specific suppression of local immune response at materno-foetal interface Transfer of antibodies IgG Haemolytic disease - ABO antibodies don't cross, Rhesus antibodies do Graves/Hashimoto's thyroiditis - Antibodies cross placenta, stimulate TSH receptors or destroy foetal thyroid
54
What is the purpose of antenatal screening?
History & examination - risk factors e.g. gestational diabetes Blood test - Blood group, Hb, Infection Urinalysis - Protein
55
What changes occur during a pre-eclamptic pregnancy?
``` Vasoconstricted Plasma - contracted Raised BP Proteinuria Pitting oedema ```

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