Antenatal Dx of Congenital Abnormalities

Question 1

describe the possible causes of congenital abnormalities

Answer 1

Chromosomal (10%) = Trisomy 21, Trisomy 13 & 18, XXY (Kleinfelter’s), Monosomy X (Turner’s)

Single gene (4%) = AD, AR etc., Thallassaemia, CF, Fragile X

Tertogen (4%) = pre-conception & T1, drugs & alco

Infections = TORCH, Varicella, Syphilis

Familial (14%)

Multifactorial (23%) = NTD’s, maternal dx (DM etc.)

Unknown (40%)

Question 2

understand the tests used to detect abnormalities

Answer 2

Bloods

• PAAP-A + B-hCG (T1)
• alpha-FP, inhibin-A, unconjugated oestridiol, free B-hCG (T2)
• cf-DNA (free fetal DNA in maternal serum)

US

• morphology scan (20wks): number fetus’, dead/alive, placenta position, abnormalities (anencephaly, IUGR)
• NT: larger NT –> consider diagnostic tests for DS
• soft markers DS = nasal bone measurement,
• DV flow: abnormal ductus venosus flow may suggest cardiac abnormalities

Question 3

distinguish between screening and diagnostic tests

Answer 3

Screening = cheap, simple & safe, gives idea of ‘risk’ - normal or high

Diagnostic = CVS & amniocentesis - invasive, used to confirm diagnosis

Question 4

appraise the advantages and disadvantages of antenatal screening and diagnostic tests

Answer 4

Adv screening: early detection high risk individuals
Disadv screening: false pos create unnecessary worry

Adv diagnostic: options ToP
Disadv diagnostic: invasive, risks miscarriage involved (CVS 1%, amniocentesis 0.5%)

Question 5

describe the options available when a congenital abnormality is detected

Answer 5

1. Cont pregnancy, aware of LT effects on child & family members as guardians

2. ToP:  earlier preg can use D&C / suction
late detection (usually if amniocentesis 15-20wks), then Mifepristone (IOL)

Question 6

recognise the difference between primary and secondary prevention of abnormalities and can provide
examples of both

Answer 6

Primary - preventing development abnormalities, e.g. avoid teratogens (alcohol, roacutane), optimise maternal health (DM, HTN, BMI), age (conception <35), folate, immunisations (rubella, varicella)

Secondary - screening ASAP to try & avoid sequelae, so CFTS & MSST (T2)