Chapter 9 (Meiosis, growth + development PART 2) Flashcards
What measurements can ultrasound scans (USS) provide
- Crown-rump length
- Biparietal diameter
- Femur length
What is crown-rump length
Length of fetus along the longest axis from head to bottom.
What is Biparietal diameter
Maximum width of the head at the widest point
Other information obtained from USS
Number of babies mother is carrying
Structure + development of key organs (seen after 18 weeks)
Blood flow through umbilical cord, which indicates oxygen + nutrient delivery
Position of placenta to see if Caesarean section is needed.
what is CVS
Chorionic Villus sampling (CVS)
When is CVS offered
- During pregnancy to check if baby has genetic disorder, eg, Down’s syndrome, sickle cell anaemia
- If woman has had previous pregnancy with these problems.
- If family history of genetic condition
- If abnormality is detected in baby during routine ultrasound scan.
Procedure of CVS
- Removal + testing of small sample of cells from chorionic villi in placenta
- between 11th + 14th weeks of pregnancy
- takes 10 mins
sample analysed - karyotyping
What are the two types of CVS
Transcervical CVS
- tube/ forceps inserted through cervix.
Transabdominal CVS
- Needle inserted through abdomen into uterus
Results from CVS info
after 3 days
results indicate if baby has major chromosome condition
rarer conditions can take 2-3 weeks.
risks/ disadvantages with CVS
increase risk of miscarriage ( higher than amniocentesis)
infection due to procedure
risk of limb defects to baby and increase in risks when carried out before 9 weeks
Not always available
can’t be used to detect neural tube defects
Benefits of CVS
- early diagnosis of chromosomal abnormality + genetic defects
- enables parents to make informed decision about pregnancy
- results (after 3 days) quicker than amniocentesis
- very accurate
Techniques to sample cells from a fetus
Chorionic villus sampling ( CVS )
Amniocentesis
When is amniocentesis offered
When factors that increase risk of abnormality are present:
- the mother is over 35
- the mothers medical history
- family history of inherited genetic conditions
Procedure of amniocentesis
- quick, around 10 mins
- carried out during 15-20 weeks of pregnancy
- Needle is used to extract sample of amniotic fluid (contains cells shed from fetus)
- sample is analysed - karyotyping
What is the ultrasound scan used for in amniocentesis
Check position of fetus
Find best place to remove some amniotic fluid
Ensure needle can pass safely through walls of abdomen + womb
Results of amniocentesis
After 3 days
Nearly 100% accurate but only tests for Down’s, Edward’s, Patau’s syndrome
For full test, cells from sample are grown for 10 days , so results ready in 2-3 weeks
Risks/ disadvantages of amniocentesis
Invasive procedure
risk of miscarriage
risk of Bacterial infection
Sensitising complications if baby is Rh+ and mother is Rh-
Having amniocentesis before 15 weeks increases risk of unborn baby developing club foot
It is carried out later in pregnancy than CVS, so less decision time as closer to abortion limit.
Benefits of amniocentesis
- diagnosis of chromosomal abnormality
- diagnosis of certain genetic defects
- enables parents to make informed decision about pregnancy
- more widely available than CVS
- Lower risk of miscarriage than CVS
- Quick
- can be used to show neural tube defects
Advantages of ultrasound scans?
Available from 10 weeks of pregnancy
Very widely available
non-invasive
lower cost
scans are painless and safe
Disadvantages of ultrasound scans?
Can only diagnose visible defects
Will not detect chromosome mutations
What does amniocentesis test
whether fetus could develop or has developed an abnormality or serious health condition
similarities between CVS and Amniocentesis procedures
- Require genetic counselling before test
- Are invasive diagnostic antenatal tests
- Enable parents to make informed decision about pregnancy, by having genetic counselling after results
- both quick, around 10 mins
Similarities in the purpose of both CVS and amniocentesis?
Both are diagnostic tests that are used when there is:
- Advanced maternal age
- Past history of genetic/chromosomal abnormality
- Biochemical/molecular diagnosis of a familial genetic disorder.
Different types of Ultrasound scans
Transabdominal ultrasound
Transvaginal ultrasound
Fetal echocardiography
What is the purpose of the dating scan
Confirms pregnancy
checks Fetal heartbeat
determines gestational age + estimates due date
Checks for multiple pregnancies
Diagnoses ectopic pregnancy or miscarriage
What is the purpose of the mid pregnancy scan
Monitors fetal growth and position
determines sex of fetus
confirms multiple pregnancies
Check for Down’s syndrome characteristics
Monitors blood flow in umbilical cord
what is a fetal echocardiography
- Performed if doctor suspects fetal congenital heart defects
- Captures an in-depth image of the fetus’ heart and shows how it is functioning
Advantages of USS
safe
non-invasive
accurate
cost-effective
real-time images
How to calculate growth rate from a growth chart
Draw a tangent
Rate = gradient.
UNITS
What is karyotyping
The process of photographing the chromosomes of a cell organised into pairs and arranged in order of size to identify chromosome abnormalities as the cause of malformation or disease
–> chromosomes are photographed during metaphase of mitosis ( as they are at their shortest+ most condensed)
Photograph is a karyogram
What is pre-conceptual care?
The advice given to a woman planning to become pregnant.
Aim - maximise health outcomes for baby and expectant mother.
Enable interventions to identify and modify biochemical, behavioural and social risks to the woman’s health or pregnancy outcome.
At each antentatal visit, the mother will…
Be given specific advice
Be weighed
Have her blood pressure monitored (as an indicator for pre-eclampsia)
Have a sample of urine tested (for presence of glucose or protein)
- Why should parents stop smoking?
Both parents advised to stop, as both mainstream and side-stream smoke can cause harm to unborn baby, as it contains nicotine and carbon monixide.
Could increase risk of:
- Low fetal birth weight
- Miscarriage
- Perinatal mortality
- Still birth
- Sudden Infant’s death syndrom SIDS (cot death)
- Reduction in fetal lung size.
Main areas for pre-conceptial care?
Effect of:
Smoking -> CO, Nicotine
Alcohol
Rubella
rhesus sensitisation
Importance of PCC from individual’s perspective?
- The time when women and partner self-identify they want to become pregnant
- This might not coincide with cessation of contraception use.
Effect of CO on pregnancy?
CO binds irreversibly and more readily than O2 to haemoglobin and forms carboxyhaemoglobin (COHb)
Prevents binding of O2 to Hb (oxyhaemoglobin), so reduced transport and delivery by maternal blood to fetal tissue.
Leads to mild hypoxia in fetus
Less energy available for aerobic respiration
Less eneryg released for tissue growth, so less growth of individual.
Increased risk of carboxyhaemoglobinemia, which leads to increased risk of clot forming.
Why is rubella harmful during pregnancy?
Prospective mother advised to check for immunisation against rubella virus -> can cross placenta and infect fetus.
If without immunity, vaccinated more thatn 3 months before conception
Increase intake of folic acid
Can cause brain, ear, eye and heart development _> brain damage and deafness ( if expectant mother catches viral infection in first three months)
Importance of PCC from the population’s perspective?
- Accounts for women of childbearing age.
- It recognises time required to develop healthy behaviours and reduce risk factors, eg obesity.
Effect of nicotine during pregnancy?
Causes vasocontriction of arterioles
This reduces supply of O2 across placenta to fetus
Nicotine also stimulates secretion of adrenaline -> higher fetal heart rate.
Increased stunted fetal growth
Low birthweight
SIDS
Why is alcohol harmful during pregnancy?
Prospective mother advised less than 2 units per week.
Moderate consumption - Language and speech problems
Higher consumption, increase in baby developing language and speech difficulties.
Ethanol diffuses across placenta and can delay fetal development
> 6 units per week -> increase in risk of FAS.
Effect of FAS on developing fetus:
- Reduced birth weight (reduced growth)
- Heart defects
- Poor muscle tone
- Short nose, celft palate, receding chin
- Abnormal limbs
- Poor development of nervous system.
Info on folic acid during pregnancy?
Lack of folic acid -> neural tube defects.
Take folic acid tablets before conception, reduces risk of spina bifida.
Continue with supplements for first 12 weeks of pregnancy
Higher dose if:
- woman has diabetes
- previously had pregnancy affected by neural tube defects.
What is antenatal care?
Care received by pregnant women in order to ensure the best health condition for both mother and baby during pregnancy.
Includes:
Risk identification
Prevention of diseases.
- Dietary advice
- Blood tests
- Urine tests
- Weight
- Blood pressure
- Rhesus status
- Specific infections
- Genetic defects of fetus
Info on urine test and pregnancy?
Diabetes (if glucose present in urine)
Kidney disease/hypertension (if protein in urine)
Blood pressure and pregnancy?
Pre-eclampsia (indicated by high blood pressure)
Blood tests and pregnancy info?
Determine mothers blood group ABO blood-test in case of transfusion
Determine presence of any infections eg, STD → Syphilis, HIV, rubella.
Blood glucose test can indicate diabetes.
Specific infections and pregnancy?
Eg, toxoplasmosis: Parasite carried in raw meat, unpasteurised dairy products (and animal faeces)
Infectious disease blood test (HIV, syphilis) .
Diet and pregnancy information?
Increase intake of omega fatty acids → aids development of nervous system
Avoid soft cheese, smoked fish and precooked meats
Expectant mother doesn’t need to eat for two.
Role of protein for developing fetus?
Growth of baby, uterus and placenta
Production of fetal haemoglobin, enzymes and antibodies
Milk production in last stage of pregnancy
Role of calcium for developing fetus?
development of fetal strong teeth and bones
Needed for muscle development
Development of fetal nervous system
Milk production in last stage of pregnancy
Role of phosphorus for developing fetus?
Needed for bone development
Role of vitamin A for developing fetus?
Production of rhodopsin - pigment in rod cells of retina
Required for transcription
Synthesis of myelin sheath around fetal neurones
Role of Vitamin C for developing fetus?
Production of collagen in skin, tendons, bones, blood vessels
Role of Folic acid for developing fetus?
Required for DNA synthesis, cell division, red blood cell production
Prevents neural tube defects and spina bifida
Role of omega 3 fatty acids for developing fetus?
For brain and nervous system development.
Needs for mother during pregnancy?
Calcium - for milk production and maintain maternal bone
Essential aa and fatty acids to maintain maternal bone
Omega fatty acids for milk production.
Obtaining samples for karyotyping?
During pregnancy the test can be performed on a sample of:
- Amniotic fluid (from amniocentesis)
- Placenta tissue (from CVS)
- blood (from blood sample)
- bone marrow (from bone marrow biopsy)
Key chemicals used in karyotyping?
Phytohemagglutin promotes mitosis
Colchicine - prevent spindle fibres from being formed →stops cell cycle in metaphase.
Dilute salt solution - Absorbs water by osmosis, RBC rupture but in WBC it causes chromosome to spread out
Giemsa stain → shows up banding on chromosomes more easily for separation and arrangement in pairs
Karyotyping procedure?
Specimen grown in tissue culture
Cells harvested
Cells treataed with phytohemagglutin, causing cells to divide by mitosis
Colchine added to prevent spindle fibres from being formed
Cells placed in dilute salt solution → Absorb water by osmosis
Caues chromosomes to spread out, so when stained, they can be observed by a microscope.
They are arranged in order of size and paired by relative size, bands and centromere position.
Normal karyotype?
46 chromosomes grouped as 22 matching pairs or autosomes and 1 pair of heterosomes.
Abnormal karyotype?
More or less than 46 chromosomes
What do percentiles mean on growth chart?
97th percentile means 97% fetus’ measurements below 97 percentile line
Calculating growth rate on growth chart
Change in length/ no. weeks
x 100.
mmweek-1
Rhesus sensitisation information?
If Rh+ and Rh- woman becomes pregnant with Rh+ fetus:
In the first pregnancy, a portion of fetus blood (Rh+) mixes with mother’s blood.
This stimulates mother’s immune system to produce rhesus antibodies against the antigens of rhesus factor which do not harm this embryo.
This is the mother becoming sensitised.
These rhesus antibodies remain in mother’s blood, so in second pregnancy, if fetus is Rh+, some pre-existing rhesus antibodies move from mothers blood to blood of fetus across her placenta.
This antibody-antigen interaction causes disintegration of fetus red blood cells.
This results in severe anaemia in fetus that may lead to its death.
Treatment of rhesus sensitisation?
The expectant mother is injected with anti-Rh antibodies
After any potentially sensitising incident
And routinely after childbirth.
What is rubella?
Prospective mother advised to check for immunisation against rubella virus.
The virus can cross the placenta and infect the fetus.
Women without immunity should be vaccinated more than 3 months before conception
Increase folic acid uptake
Rubella can affect brain, ear, eye and heart development.
How does something travel from the mother to the fetus.
Maybe alcohol - Check!!!!
