8) Pregnancy Flashcards
On what day does the blastocyst implant into the endometrium of the uterine cavity?
Day 6 (after fertilisation)
What does further embedding of the blastocyst into the endometrium rely on?
Invasive property of trophoblast cells
Outer layer of syncitiotrophoblast
Underlying cytotrophoblast
By what day is the blastocyst fully embedded within the endometrium?
10th day after fertilisation
Implantation is interstitial, what does this mean?
Uterine epithelium is breached & conceptus implants within stroma
The placenta is haemomonochorial. What does this mean?
One layer of trophoblast separates maternal blood from foetal capillary wall
What are the aims of implantation?
Establish the basic unit of exchange (Primary, secondary & tertiary villi)
Anchor the placenta
Establish maternal blood flow within the placenta
What are the differences between primary, secondary & tertiary villi in the conceptus?
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)
How is the endometrium of the uterus prepared for implantation?
Decidualisation
Remodelling of spiral arteries
What is decidualisation (of the uterine endometrium)?
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
How are the spiral arteries of the endometrium remodelled in preparation for implantation?
Creation of low resistance vascular bed
Maintains high flow required to meet foetal demand particularly late in gestation
What implantation defects can occur?
Ectopic pregnancy (most commonly F. tube) Placenta praevia Incomplete invasion (placental insufficiency, pre-eclampsia)
What is placenta praevia?
Implantation in the lower uterine segment
Can cause haemorrhage in pregnancy
Requires C-section delivery
Describe the structure of the placenta by the beginning of the 4th month
- Foetal portion
Formed by chorion frondsum, bordered by chorionic plate - Maternal portion
Formed by the decidua basalis
The decidual plate is most intimately incorporated into placenta
In the placenta, what lies between the chorionic & decidual plates?
Intervillous spaces
Filled with maternal blood
During the 4th & 5th months, what happens to the placenta?
Decidua form decidual septa
Septa project into intervillous spaces but don’t reach chorionic plate
Septa divide placenta into compartments - Cotyledons
Throughout pregnancy how much of the uterus does the placenta cover?
15-30% of the internal surface of the uterus
Describe the first trimester placenta
Placenta established
Placental ‘barrier’ to diffusion still relatively thick
Complete cytotrophoblast layer beneath syncytiotrophoblast
Describe the placenta at term
Surface area for gas exchange dramatically increased
Placental ‘barrier’ now thin
Cytotrophoblast layer beneath syncytiotrophoblast lost
Describe the arrangement of foetal blood vessels within the placenta
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
How do cotyledons receive their blood supply?
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
What factors influence the passive diffusion of substances across the placenta?
Concentration gradient
Barrier to diffusion (placental membrane thins as foetal demands increase)
Diffusion distance (haemomonochorial)
Which substances are transported across the placenta?
- Simple diffusion water, electrolytes, urea & uric acid gases (flow-limited) - Facilitated diffusion Glucose - Active transport Amino acids, iron, vitamins
What are teratogens?
Substances or environmental agents which cause the development of abnormal cell masses during foetal growth, resulting in physical defects in the foetus
Name some common teratogens
Thalidomide Alcohol Therapeutic drugs Drugs of abuse Maternal smoking
Which pathogens are able to cross the placenta?
Varicella zoster Cytomegalovirus Treponema pallidum Toxoplasma gondii Rubella
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
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
What is the function of human chorionic somatomammotrophin?
Influences maternal metabolism
Increases availability of glucose to foetus
During pregnancy where is progesterone produced?
Corpus luteum up to week 11
Placenta takes over production
Influences maternal metabolism, increased appetite
Apart from protein & steroid hormones, what else does the placenta synthesise?
Glycogen
Cholesterol
Fatty acids
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
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
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
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)
Physiological changes take place in which main systems of the body during pregnancy?
CVS Urinary Respiratory GI Immune Metabolic changes - carbohydrate, thyroid hormones
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%
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
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
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
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)
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-
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
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
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
What risks are associated with poor control of gestational diabetes?
Macrosomic foetus
Stillbirth
Increased risk of congenital heart defects
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
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!)
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
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
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
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)
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
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
What is the purpose of antenatal screening?
History & examination - risk factors e.g. gestational diabetes
Blood test - Blood group, Hb, Infection
Urinalysis - Protein
What changes occur during a pre-eclamptic pregnancy?
Vasoconstricted Plasma - contracted Raised BP Proteinuria Pitting oedema
