Obstetrics - Antenatal screening tests Flashcards
Anaemia during pregnancy
Common causes
Cut-off
Screening period
Common causes:
- Physiological hemodilution (physiological anaemia with continuous drop till 30-34w then plateaus till term)
- Iron deficiency anemia
- Thalassemia
Cut-off: Hb <10g/dL
Screening: CBC at booking then repeat 28w
Reasons for screening for thalassaemia in antenatal visits
Method for screening
Protocol for screening - MCV at booking visit → confirm thal trait by Hb studies and Fe profile
Reasoning:
- Both of couple are α- or β- thalassaemia carriers, offspring has 1/4 chance of suffering from α-thalassaemia major or β-thal major
- α-thalassaemia major is usually NOT compatible with life (develops hydrops fetalis); β-thal major is a debilitating disease
- Mother carrying affected fetus has 50-60% chance of developing serious obstetric Cx, eg. pre-eclampsia, postpartum haemorrhage
Method for pre-natal diagnosis of a-thalassaemia
≥18w
- serial USG at referral and 30w for features of thal major
- Features of α-thal major: cardiomegaly, placentomegaly, fetal growth retardation, hydroptic changes
- NO invasive test if normal USG findings → cord blood at delivery for Hb study confirmation
<18w
- offer prenatal diagnostic technology or serial USG
- CVS (10-12w) or amniocentesis (18w) for DNA study to screen for SEA gene deletion (majority)
- Serial USG at 13, 16, 20, 30 weeks
Method for pre-natal diagnosis of B-thalassaemia
Strategy for prenatal diagnosis: by DNA study via CVS/amniocentesis (can dx in 95% cases)
≥10 common mutation in this locality → require DNA study of couple first to identify responsible mutation
If mutation not detected, then prenatal diagnosis may not be possible
Workup if couple is discordant for thalassaemia carrier status
If couple is discordant for thalassaemia carrier status, then one would need to identify the genotype of β-partner
- Note that for compound heterozygote, only the β-allele would be manifest in Hb studies
- no imbalance → no HbH inclusion bodies → alpha-thal trait cannot be detected
Strategy for prenatal diagnosis:
- ≥18w - serial USG at referral and 30w for features of alpha thal major
- <18w - DNA study of β partner followed by prenatal diagnostic technology
Workup if couple is B-thal carrier + HbE
If couple is β-thal carrier + HbE, offspring has 1/4 chance of HbE β-thal
Prenatal diagnosis is indicated because HbE β-thal has a variable presentation
most severe children may be transfusion-dependent
Strategy for prenatal diagnosis - by amniocentesis/CVS + DNA study
Outline the screening protocol for anaemia in antenatal care
Screening protocol in HK: CBC at booking then repeat 28w
Symptoms of anaemia
Symptoms of anaemia: due to ↓O2 delivery, depends on onset and severity of anaemia
□ Acute/severe: SOB (esp on exertion), palpitation, dizziness/syncope (may be postural)
□ Chronic/insidious: fatigue, ↓exercise tolerance, SOBOE, pale-looking
□ Symptoms from causes, eg. menorrhagia, tarry stool, bone pain, hypovolaemia
□ Complications: cardiac ischaemia, ↑thrombocytopenic bleeding, ↑mortality
Compare lab findings of IDA vs Thalassaemia
Hemolytic disease of newborn
Pathophysiology
Sensitization: in 1st pregnancy
- Rh(D) -ve mother carry a Rh(D) +ve fetus
- sufficient amount of fetal cells gain access to maternal circulation (sensitization event)
→ mother produce immune response vs Rh(D) antigen
→ fetus is NOT affected as initial response is weak and majority of Ab are IgM Ab (not cross placenta)
Hemolysis: in subsequent pregnancies (or after sensitizing events), esp get worse with repeated pregnancies
- 2° immune response is mounted → large amounts of IgG anti-(D) Ab produced
- these IgG Ab can pass through placenta → causes fetal hemolysis → severe anemia → fetal death
For ABO blood group, HDN can occur but typically of a milder severity (mild hemolysis w/ jaundice) because
- most anti-A and anti-B are IgM → do not cross placenta
- A and B antigen are not fully developed in fetus
Sreening protocol and management for HDN
- Timing for screening
- Prophylaxis during pregnancy
- Different management for Rh(D) +ve vs -ve mothers
- Post-partum prophylaxis
Screening protocol: ABO + Rh blood group at booking visit (or non-booked when admitted to obstetrics ward)
For Rh(D)-ve mothers, refer to prenatal dx clinic for F/U and perform
- red cell antibody screening: typically from previous blood transfusion
- anti-D antibody titer: repeat at 28-30w for any isoimmunization (before giving anti-D prophylaxis)
- Management: Antenatal prophylactic IM anti-D: to wipe out D-antigen in maternal blood
For anti-D +ve (sensitized) pregnant mothers.
- check father’s Rh(D) status → worry if father Rh(D) +ve
- monitor maternal anti-D titers Q2-4w from booking → ↑risk of HDN if rising maternal titers
- examine baby for signs of anemia → non-invasive assessment by MCA Doppler (sen 100% spe 88%)
- Management: delivery if term or near term, fetal blood transfusion if too premature
Post-partum prophylaxis:
- take cord blood for CBC, hemolysis markers (bilirubin, reticulocytes), Rh grouping
- take maternal blood for anti-D, Kleihauer (pref ≤2h)
- Rh(D) +ve baby → give 1 dose anti-D (or higher according to Kleihauer’s test)
Sensitizing events that indicate Rh(D) screening/ indications for Rh(D) testing
Antenatal prophylactic IM anti-D has NO USE if already sensitized (as indicated by ↑maternal anti-D titers)
Outline testing protocol if sensitizing event for HDN occurs after 20 weeks gestation
Screening protocol for RBC Ab testing (other antibodies if Rh(D) negative)
Management of positive RBC Ab
Screening protocol: RBC Ab testing for non-Chinese and all Rh(D) -ve
Aim: as part of type (ABO/Rh) and screen (for RBC Abe.g. D,c, K, Fy, Jk…etc)
- speed up provision of compatible blood for obstetric emergency
- screen for fetal anemia or HDN
If positive, then
- offer further characterization of nature of Ab
- counsel on potential effects:
- non-specific → no further action
- potential effect on X-M → explain, issue X-M card by blood bank if Ab is very rare
- potential to cause HDN → refer to PDC (prenatal dx clinic) for prenatal dx of HDN
Follow-up:
- Ab testing for Ab titers
- US for any signs of fetal anemia
Outline flowchart for type and screen testing during antenatal screening
List infections screening during antenatal care
Rubella: Rubella Ab IgG at booking visit
Syphilis: VDRL at booking visit
HIV: HIV Ab at booking visit
Hepatitis B: HBsAg at booking visit
Group B Streptococcus (GBS): Routine screening recommended at 35-37w via low vaginal swab (LVS) at vaginal introitus and rectal swab by inserting through anal sphincter
Rubella infection
- Risk of congenital rubella
- S/S of maternal rubella
- Screening and diagnosis
- Management of rubella infection
Congenital rubella:
- commonly congenital cardiac lesions, cataract, microcephaly, mental deficiency, SN deaf-mutism
- Risk of malformations depends on gestational age at time of attack by virus, earlier infection = miscarriage, stillbirth, congenital rubella syndrome higher anomaly rate
- Risk to pregnancy: miscarriage, stillbirth, congenital rubella syndrome
S/S of maternal rubella:
- asymptomatic (25-50%), fever, malaise, LN, diffuse fine MP rash (start on preauricular/face and generalized ≤24h, last 1-3d), polyarthritis, polyarthalgia
Screening:
- Rubella Ab IgG at booking visit
- review rubella Ab status of AN bloods: >1:10 = immune → no risk
Diagnosis:
- asymptomatic, repeat rubella Ab 21-24d after exposure
- symptomatic, diagnosis of rubella can be made by - specific IgM Ab 5d after appearance of rash
- ↑IgG Ab between acute (7-10d after onset) and convalescent titers (2-3w later)
Management:
- If -ve (non-immune), prevent infection of mother: avoid infectious contacts, avoid crowded places…
- vaccination after pregnancy: should undergo contraception ×1m after vaccination
- if rubella infection <12w → decide on whether to seek TOP
Outline flowchart for maternal rubella
Indications and contraindications for GBS intrapartum antibiotics prophylaxis
IAP regimen for GBS infection
Risk factors of Down syndrome
Gestational diabetes mellitus
- Risk factors
Gestational diabetes
screening timing recommendation
Diagnostic criteria
Recommended timing for screening:
high risk: 75g OGTT between booking visit and 16w → if -ve, repeat at 28-32w
low risk: 75g OGTT 28-32w (or asap if book after 32w)
Neural tube defects
- Screening test
- Examples
- Prevention
Screening: high titer AFP
Prevention: periconception folate supplement
0.4mg/d: for normal risk
5mg/d: for personal Hx or prev child with NTD, AED (esp Epilim, Tegretol), antifolate drugs…
Abdominal wall congenital defects
- Examples
- Detection
Risk factors for congenital abnormalities
Screening protocol for congenital abnormalities
Management of congential abnormalities
Counselling and continue monitoring of condition
Further assessment and PN diagnosis
- DNA study for suspected chromosomal abnormalities (amnio, CVS, NIPT)
- serial US for suspected structural abnormalities → growth, progression
Options for pregnancy: depend on nature of anomaly
Surveillance for maternal vascular disease
Surveillance for twins
Surveillance for HDN
Modalities of fetal health assessment
Ultrasound examination: for
- fetal growth parameters: SGA, LGA, IUGR, macrosomia
- amniotic fluid volume (AFV): single deepest pocket, AFI
Others
- Antepartum cardiotocography (CTG): i.e. non-stress test
- Doppler blood flow patterns
- Biophysical profile
Chorionic villus sampling
Timing during pregnancy
Risk of miscarriage
Procedure
Workup tests
Amniocentesis
Timing
Risk of miscarriage
Procedure
Risks
