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 SE asian type gene deletion on HBA1/2 (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
Syphilis
- Screening test
- Management of positive test
- Risks to pregnancy
- Confounding factors for false positive
Screening: VDRL at booking visit
Management:
- confirm with treponemal test: FTAAbs - Fluorescent treponemal antibody absorption test
- treatment of maternal syphilis: by single / two doses of IM penicillin
Risk to pregnancy:
- Congenital syphilis: hydrops fetalis, nasal discharge, hepatomegaly, rash, petehial rash, ostitis/ periostitis…
Confounding factors:
- other treponemal infection (endemic in some countries)
- successfully treated past syphilis: usu -ve after 6m
- medical conditions, e.g. autoimmune ds (SLE), other STDs, febrile illness (malaria, viral pneumonia)
HIV
- Screening test
- Management of positive result
- Intrapartum and postpartum prophylaxis
Screening protocol: HIV Ab at booking visit
Counselling on HIV screening during pregnancy
- +ve results: mean infection
- mother-to-child transmission (MTCT) occur in 15-40% of infected women
- -ve results: repeat after 3m if high suspicion
Management:
- Consult Integrated Treatment Center (ITC), DH or Special Medical Center (SMC), QEH/PMH for intra-partum antiviral regimen
Intrapartum prophylaxis:
- regimen: - zidovudine: IV bolus 2mg/kg then 1mg/kg/h till delivery
- lamivudine: 150mg PO Q12h till delivery
- nevirapine: single dose 200mg PO
- raltegravir: 400mg PO Q12h till delivery
- timing: started at onset of labor (or asap) or 3h before elective C/S
Postpartum prophylaxis:
- zidovudine: 300mg PO BD for 7d
- lamivudine: 150mg PO BD for 7d
- duration: for 7d before referral to HIV physician
HIV
Intrapartum care plan
Avoid: fetal scalp blood sampling, scalp electrode insertion, rupture of membrane
Caesarean section: offered unless prolonged ROM, labor is advanced, before adequate combination antiretroviral therapy (cART) given (no benefit)
Avoid breastfeeding for infected mothers (except if no alternative, if on cART then risk is much lower anyway)
Hepatits B
- Screening protocol
- Management
Screening protocol: HBsAg at booking visit
For infected mothers,
- for infants give 1 dose of HBIG (and routine HBV vaccination) at birth → ~95% efficacy
- for mother, give TDF if HBV DNA >2×105U/mL
- start in last trimester (↓teratogenic effects, also take 8w to work)
- stop 3m after delivery (↓risk of inducing flare with ↑risk post-partum)
efficacy: reduce transmission rate from up to 90% to 2.9-6.8%
note: breastfeeding safe
GBS
- Risk to pregnancy
- ## Screening protocol
Group B streptococcus (GBS) = Streptococcus agalactiae
- Reservoir: GI tract (1° reservoir, in 20-40% adults), vaginal colonization (10-30% of pregnant women)
- Maternal risks: UTI, PROM/PPROM, preterm labor, chorioamnionitis, post-partum endometritis
- Neonatal infection: ~1/1000 births in HK, contracted during delivery, risk of early onset inf’n 1-2% in colonized mothers
- Aim of screening: to justify use of intrapartum Abx prophylaxis (IAP) for prevention of neonatal GBS disease in the newborn
Screening protocol:
- Routine screening recommended at 35-37w
- Hx of GBS colonization in previous pregnancies/ previous baby with GBS colonization but w/o invasive neonatal GBS disease
- +ve GBS culture before pregnancy (i.e. not in this pregnancy)
- Swab procedure: swab at 2 separate locations (without speculum): low vaginal swab (LVS) at vaginal introitus - rectal swab by inserting through anal sphincter
- put both inside a single special broth culture medium
- send for C/ST: sensitivity to penicillin, clindamycin and erythromycin will be routinely performed in +ve cases
Indications and contraindications for GBS intrapartum antibiotics prophylaxis
IAP regimen for GBS infection
Down syndrome screening
- Screening protocol
Screening protocol: voluntary, two tier
1st trim screening (1TDS) (早孕期篩查): offered routinely at 11w to 13+6w → detect ~90% DS babies
- nuchal translucency (頸皮厚度): increased
- maternal serum PAPP-A (妊娠相關血漿蛋白): decreased
- maternal serum free β-hCG (絨毛膜促性腺激素水平): increased
2nd trim screening (2TDS) (中孕期篩查): offered if book late (or no appointment for 1TDS) at 16-19+6w → detect ~80% DS babies
- maternal serum AFP (甲胎蛋白): decreased
- maternal serum free β-hCG: increased
- maternal serum μE3 (unconjg’d estriol) (雌三醇): decreased
- maternal serum dimeric inhibin A (抑制素A): increased
non-invasive prenatal testing (NIPT) (無創性胎兒染色體篩查): Cell-free fetal DNA in maternal blood → done in private depending on maternal wish (offered for high risk after 1TDS)
Routine anomaly scan at 18-20w
Risk factors of Down syndrome
Down syndrome inheritance
Trisomy 21 (21-三體綜合症) (47,+21): 95%
- meiotic dysfunction (90% from mother)
Robertsonian translocation involving chr21: 3-4%
- Between chr13, 14, 15, 21, 22 acrocentric chromosomes
Trisomy 21 mosaicism (47,+21/46): 1-2%
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)
Congenital abnormalities
- Most common congenital defects
- Incidence of fetal abnormality
Commonest 4 groups of defects = Neural tube defects (3-7/1k), cardiac (6/1k), DS (1.5/1k), cleft lip/palate (1.5/1k)
Neural tube defects: e.g. Anencephaly, Microcephaly, Spina bifida, Holoprosencephaly, Hydranencephaly
Cardiac defects: ASD, VSD, Congenital PS/AS, Coarctation of aorta, Transposition of arteries, ToF
Fetal abnormality is found in
- >50% of conceptions, 1-2% of births (major + minor)
- ~70% miscarriages, 15% deaths from 20w gestation to 1y postnatal
- 8% special needs/disabled children
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…
Congential cardiac defects
Common defects
Detection
Congenital cardiac defects:
Commonest: VSD, ASD, congenital PS/AS, coarctation of aorta, transposition, Tetralogy of Fallot
Detection:
- anomaly scan 18w: four-chamber view, IUGR, oligohydramnios
- after delivery: neonatal HF
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
Fetal health and growth screening
- Protocol
- Modalities of assessment
Screening in low risk pregnancies:
- Maternal vigilance for fetal activity over 2nd half of pregnancy
- Regular SFH measurement every AN visit
- Auscultation of fetal heart every AN visit
Modalities of assessment:
Ultrasound examination: for fetal growth parameters: SGA, LGA, IUGR, macrosomia/ amniotic fluid volume (AFV): single deepest pocket, AFI
Antepartum cardiotocography (CTG): i.e. non-stress test
- cardio-: monitoring of fetal heart rate
- tocography: monitoring of uterine contractions
Doppler blood flow patterns
Biophysical profile
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
Cordocentesis
- Timing
- Risk of miscarriage
- Procedure
Cordocentesis:
Timing: 20w
Risk of miscarriage: 2-5%
Principle: when fetal blood is required for prenatal testing, e.g. for platelet count when suspecting alloimmune thrombocytopenia
Procedure: US-guided needle passage into umbilical cord where it insert into placenta (fixed)
