downs testing + pregnancy Flashcards
naegele’s rule
predicts estimated due date based on onset of womens last menstrual period
add nine months to get due date - 280days
when is the site “rechecked” in placenta praevia?
at 32wks by US
initial antenatal screening for downs syndrome
all offered, indicates risk - NOT diagnostic
older mothers have higher risk
combined test
quadruple test
both return either a low or high chance result
- low -> 1 in 150 or more -> 1 in 300
- high ->1 in 150 ir less -> 1 in 100
combined test
first line
done between 11-13+6wks
involves combing results from
- nuchal translucency measurement - <3.5mm (normal when CRL is 45-84mm)
- serum beta-HCG
- PAPP-A
combined test results in Down’s vs Trisonmy 18(Edwards) + 13(patau)
downs
- increased HCG
- DECREASED PAPP-A
- thickened nuchal translucency (>6mm)
trisomy 18 (Edward) + 13 (patau)
- similar results but HCG tends to be lower
quadruple test for downs
if women book later in pregnancy - offered between 15-20wks
maternal blood tests -
- beta-HCG - higher indicates greater risk
- alpha-fetoprotein - lower
- unconjugated oestriol - lower
- inhibin A - higher
if “high risk” result in combined or quadruple test
offered:
- second screening test - NIPT
- diagnostic test - amniocentesis or chorionic villus sampling (CVS)
non-invasive prenatal screening test (NIPT)
v high sensitivity + specificity (>99%)
analysis small DNA fragment that circulate in blood of a pregnancy women (cffDNA)
- cffDNA derives from placenta cells + is usually identical to fetal DNA - analysis allows detection of certain chromosomal abnormalities
- cffDNA is detectable from around 10wks, amount rises as pregnancy continues
amniocentesis
involves US guided aspiration of amniotic fluid using a needle + syringe
- used later in pregnancy when there’s enough amniotic fluid to make it safer to take a sample
—> >15wks
miscarriage rate <1%
chorionic villus sampling (CVS)
involves US guided biopsy of placental tissue
- used when testing is done earlier**
—-> before 15wks
miscarriage rate <2%
booking visit
8-12weeks - ideally <10
- info - diet, alcohol, smooking foic acid, vit D, take Hx
- BP, urine dip, check BMI
bloods/urine
- FBC, blood group, rhesus status, red cell antibodies, haemoglobinopathies
- hep B, syphilis
- HIV offered to all
- urine culture to detect asymptoomatic bacteruria*
when is downs syndrome screening done?
11 - 13 +6wks
when is the anomaly scan done
18-20+6wks
what happens at 28wks of antenatal care
routine BP, urine dipstick, SFH
second screen for anaemia + atypical red cell alloantibodies
first dose of anti-D prophylaxis to rhesus neg women
(second given at 34wks)
how should fetal growth be monitored
serial measurement of symphysis fundal height (SFH) at each antenatal appointment from 24wks
- improve prediction of SGA neonate
plot on chart, lower than 10th centil measurement or serial static/slow growth -> refer for US
changes to pharmacokinetics in pregnancy
absorption affected by morning sickness
increased plasma volume + fat stores -> volume of distribution increases
decreased protein binding -> increased free drug
increased liver metabolism of some drugs -phenytoin
elimination of renally excreted drugs increases -> increase GFR
changes to pharmacodynamics in pregnacy
no significant changes
pregnant women may be more sensitive to some drugs - hypotension with antihypertensives in 2nd trimester
period of greatest teratogenic risk
4th-11th weeks
organogenesis
avoid all drugs if poss, unless benefit outweighs risk to foetus
teratogenic drugs
ACEi/ARB -> renal hypoplasia
androgens
antiepileptics -> cardiac, facial, limb, neural tube defects
lithium - CVS defects
methotrexate ->skeletal defects
retinoids
warfarin * -> limb+facial defects
seizures during pregnancy are assoc with what adverse effects
lower verbal IQ in child
hypoxia
bradycardia
antenatal death
maternal death
why might seizures increase by 10% during pregnancy
non-complianse
changes to plasma conc of drugs
- persistent vomiting
- increased clearing
in which trimester does blood pressure tend to drop
2nd trimester
UTI in pregnancy Mx
nitrofurantoin
trimethoprim in 3rd trimester
who should get VTE prophylaxis in pregnancy
2 or more risk factors
- obesity
- >35yrs
- smoker
- previous DVT
- Csection
at delivery + up to 7 days post partum
