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