When are the first, second and third trimesters?
1st trimester - 1 to 12 weeks
2nd trimester - 13 to 28 weeks
3rd trimester - 29 to 40 weeks
When is antenatal care given?
What is the sensitivity of a test?
Proportion of people with a disease which are detected by the test
i.e test positives / (test positives + false negatives)
What is the specificity of a test?
Proportion of patients without a disease who are identified by a test
i.e true negatives / (true negatives + false positives)
How is sensitivity calculated?
Sensitivity = (True positives) / (True positives + False negatives)
How is specificity calculated?
Specificity = (True negatives) / (True negatives + False positives)
What is the positive / negative predictive value of a test?
Proportion of positives/negatives who are actually true
e.g PPV = (True positives) / (True positives + False positives)
gives you an idea of how reliable a test is
Screening tests tend to be used to rule diseases ___.
rule diseases out
wide variety of diseases can be screened for, then if any of them are positive, a diagnostic test can be performed
When are ultrasound scans carried out in pregnancy?
20 weeks - more detailed one
To test for structural abnormalities e.g those seen in Down's syndrome
What is Naegele's rule for calculating a woman's due date?
Take date of last period
Add on nine months and seven days i.e 280 days
What are some early blood tests done in antenatal care?
Hb - for sickle cell anaemia anaemia
STIs - syphilis, HIV, Hepatitis B & C
What are the steps of antenatal abdominal examination?
Palpate - fundus, fundal height, walls for foetal lie and presentation, ballot the presenting part
Auscultate - foetal heart
What vital signs and tests are routine at antenatal appointments?
HR, BP, BMI
What is the difference between the lie and presentation of a foetus?
Lie - baby's position in the womb i.e longitudinal or transverse
Presentation - what part of the baby is most inferior i.e cephalic (head) or breech (feet)
What is a normal foetal heart rate?
120 - 160 bpm
How is fundal height measured?
Fundus of uterus to Pubic symphysis
What is the purpose of antenatal ultrasound testing?
To assess the structure of a foetus for abnormalities and treat them where possible
What is placenta praevia?
Placenta lies low in the uterus, obstructing the opening of the cervix
How can placenta praevia be detected?
What are the symptoms?
Which genetic disorder is screened for in all pregnant women?
What should couples be asked before screening for Down's syndrome is carried out?
Are you sure you want to know?
Have you considered what you would do if positive (i.e keep the baby or termination)?
If a baby having Down's syndrome would make no difference to their parents, should the mother have a screening test?
Arguably no, it makes no difference
How does maternal age influence the risk of trisomy 21?
As maternal age increases, risk of trisomy 21 increases
Which measurement on foetal ultrasound is used to estimate gestational age?
Which measurement on foetal ultrasound is used as a predictor for Down's syndrome?
Nuchal thickness / frequency (NT or NF)
What is a normal value for nuchal thickness?
< 3.5 mm
A nuchal thickness > ___ mm is suggestive of Down's syndrome.
> 3.5 mm
Which serology tests can be used along with maternal age and nuchal thickness to calculate the risk of Down's syndrome?
HCG (will be increased)
AFP (will be reduced)
PAPP-A (will be reduced)
Apart from ultrasound and serology, what sampling tests can be used to diagnose genetic disorders?
From what point in gestation can they be done?
NIPT (non-invasive prenatal testing) from 8 weeks
Chorionic villus sampling from 12 weeks
Amniocentesis from 16 weeks
What is the risk carried alongside chorionic villus sampling and amniocentesis?
Tiny percentage but still a risk