Antenatal Screening Flashcards
how do you calculate sensitivity?
true positive/(all positive + false negative)
how do you calculate specificity?
true negative/(all negative + false positive)
when is the booking visit completed?
between 8-12 weeks gestation
what four things are done at the booking visit?
history
examination
blood tests
urinalysis
what three examinations are done during the booking visit?
height
weight
blood pressure
what bloods are done at the booking visit?
haemoglobin rhesus status syphilis HIV Hep B+C
when is the first ultrasound done?
8-12 weeks gestation
what does the first ultrasound scan look for?
viability
how many
estimate gestational age
structural anomalies
when is the most accurate time to establish the EDD?
8-12 weeks
what is EDD?
estimated date of delivery
what rule can be used to calculate EDD?
naegele’s rule
what is naegele’s rule?
add on nine months and seven days/280 days to the date of onset of a woman’s LMP = EDD
when is the foetal anomaly scan done?
20 weeks
what should be investigated in a history at the foetal anomaly scan?
physical/mental health of mother
foetal movements
what examinations should be done at the foetal anomaly scan?
BP urinalysis SFH lie + presentation foetal heart auscultation
what is SFH?
symphysis fundal height
what is placenta praevia?
when the placenta is low lying in the uterus and covers the cervix
if placenta praevia is seen at 20 weeks, when is another scan done?
32 weeks
what trisomy’s can be screened for?
21
18
13
what is trisomy 21?
downs syndrome
what is trisomy 18?
Edwards syndrome
what is trisomy 13?
patau’s syndrome
what secondary screening test is offered if there is a high risk result for a trisomy?
NIPT
how is trisomy screening performed in the first trimester?
measure nuchal thickness (NT)
combine this with HCG and PAPP-A for a full assessment
when is trisomy screening done in the first trimester?
11-13+6 weeks
what is a normal result for NT in the first trimester?
<3.5mm if the CRL is 45-85mm
what is CRL?
crown rump length
what trisomy can be screened for in the second trimester?
trisomy 21
why would second trimester screening for T21 be done?
first missed
first unsuccessful
when is second trimester screening for T21 done?
15-20 weeks
what is involved in second trimester screening for T21?
blood sample for biochemical markers
look at maternal age
what biochemical markers are checked as part of trisomy screening in trimester two?
AFP
hCG
unconjugated oestradiol
inhibin A
when is further investigation for trisomy 21 done?
> 1:150 risk of the condition
how can further investigation of trisomy’s be completed?
NIPT
CVS/amniocentesis
what does NIPT stand for?
non invasive prenatal testing
what is another name for NIPT?
cell free foetal DNA testing (cffDNA)
what does NIPT detect?
foetal DNA fragments in the maternal blood
when is cffDNA detectable?
from around 10 weeks
increases as pregnancy continues
what is done if NIPT is positive for trisomy?
diagnostic testing
NIPT IS JUST ANOTHER SCREENING TEST
what are the two diagnostic tests for trisomy’s?
amniocentesis
chorionic villus sampling (CVS)
what risk is associated with amniocentesis and CVS?
miscarriage
when is amniocentesis performed?
after 15 weeks
when is CVS performed?
after 12 weeks
when is maternal anaemia screened for?
booking
28 weeks
name five risk factors for gestational diabetes
BMI >30 previous macrosomia - >4.5kg previous gestational diabetes family history of diabetes minority ethnic origin with high prevalence of diabetes
when should SFH be measured and why?
all antenatal appointments from 24 weeks
improves prediction of an SGA neonate
who should be referred for ultrasound measurement of foetal height?
one SFH < 10th gentile
serial measurements showing slow/static growthh
when can measuring SFH be difficult and what is done for these patients?
BMI>30, large fibroids, hydramnios etc.
ultrasound assessment of foetal size
what should women at high risk for pre-eclampsia take?
150mg aspirin daily from 12-36 weeks
what makes you high risk for pre-eclampsia?
hypertensive disease during a previous pregnancy CKD autoimmune disease diabetes chronic hypertension
what should women at moderate risk for pre-eclampsia take?
more than one moderate risk factor = 150mg aspirin daily from 12 weeks til birth
what makes you moderate risk for pre-eclampsia?
first pregnancy >40 pregnancy interval >10 years BMI >35 family history of pre-eclampsia multiple pregnancy
