Antenatal Care and Prenatal Diagnosis

Objectives of Antenatal care

  • Detect and manage any pre-existing maternal disorders that may affect pregnancy outcome
  • Prevent or detect and manage maternal complications of pregnancy
  • Prevent or detect and manage foetal complications of pregnancy
  • Detect congenital foetal problemsif requested by parents
  • Plan with the mother- the circumstances of birth to ensure maximum safety for the mother and baby and the maximum parental satisfaction
  • Provide advice regarding lifestyle and ‘minor’ disorders of pregnancy

  1. Booking (8 and 14 weeks)
    1. Detailed Hx and Examination
      1. Confirm dates and estimated due dates.
    2. Bloods
      1. FBC: Hb (look for anaemia- most commonly iron deficient)
      2. Blood screen (ABO/Rh)
      3. Disease screen (Syphilis; Rubella; HIV; Hep B&C)
    3. Urinalysis; MSSU C&S (protein- ?pre-eclampsia; infection)
    4. Booking USS
      1. Confirm viability
      2. Confirm/exclude multiple pregnancy
      3. Confirm gestation (head diameter/crow-rump length)
      4. +/- nuchal translucency
        1. High nuchal translucency is associated with cardiac abnormalities causing fetal hydrops (oedema)
  2. Follow-up visits
    1. Hx
      1. Physical and mental health
      2. Foetal movements
    2. Examination
      1. BP & Urinalysis (pre-eclampsia)
      2. Symphysis-fundal height (IUGR)
      3. Lie and presentation
      4. Engagement of presenting part
      5. Foetal heart auscultation
  3. Screening for foetal abnormalities
    1. USS at 18-20 weeks- picks up 40-60% of serious cardiac abnormalities
    2. Alpha-foeto-protein (AFP)
      1. AFP is secreted by the baby’s liver in utero, urinated and swallowed, then enters into the mother’s blood via the placenta

      1. AFP is raised in:
        1. Multiple pregnancy
        2. Neural tube defects e.g. spina bifida
        3. Exomphalos (and Gastroschisis)/ duodenal/oesophageal atresias
        4. Nephrosis
        5. Foetal death
      2. AFP is low in:
        1. Genetic conditions (specifically downs and trisomy 18)
    1. Down Screening
      1. Combines AFP, HCG and pregnancy-associated plasma protein A (and occasionally oestriol) at 15-20 weeks (HCG is elevated in Downs; others are generally low)
      2. Incorporated with maternal age and gestation to give a personal risk
      3. >1:250 (high risk) usually requires further investigation (see genetics in pregnancy)

      1. Nuchal Skin fold thickness is measured by USS at around 11-13 weeks if there is increased risk of Downs.

Further investigations for Prenatal Diagnosis

  • Tests can be offered if there are any abnormal screening results OR
    • If there is a family history of an inherited condition
    • If there has been a previous pregnancy with a foetal abnormality
    • If they have been exposed to illness e.g. toxoplasmosis, rubella etc during the pregnancy
    • If they have been exposed to teratogens, e.g. drugs/radiation, during the pregnancy
    • If the woman has T1DM, epilepsy or myotonic dystrophy

Antenatal genetic sampling

  • Chorionic Villous sampling (11.5 weeks +); provides good quality tissue; 1-2% risk of miscarriage
  • Amniocentesis (15 weeks +); provides poorer quality tissue but lower risk of miscarriage (0.5-1%)
  • Foetal blood sampling (18 weeks +; rarely done)

Suitable tests

Whole Genome Testing

  • Disadvantages
    • What is a genuine mutation vs polymorphism (array-CGH)
      • In general, mutations will be larger, will be de-novo (i.e. parents don’t have it) or will affect a known region/previously reported (this may mean the parents do have it- known genetic mutation)
  • Advantages
    • It can be cheap (karyotyping), and can detect chromosomal abnormalities fairly accurately

Targeted Testing

  • Only useful when you known what to look for
    • FISH is used for looking at specific chromosomal locations

Types of mutations

Chromosomal

  • Balanced vs Unbalanced
    • Allthe chromosomal is present in the correct amount (balanced)
    • Extra or missing chromosomal material (usually 1 or 3 copies of a fraction of the genome) (unbalanced)
  • Translocation (chromosomes ‘break’ and one part of the broken chromosome attaches to another ‘non-homologous’ (not the same) chromosome)
    • Robertsonian translocation
      • Commonly occurs (viably occurs) in acrocentric chromosomes (i.e. ones with one very long and one very short arm- e.g. 13, 14, 15, 21, 22) where the break is at the centromere and the long arm of the ‘broken’ chromosome is stuck onto the (effectively non-existent) short arm of another chromosome
      • This results in a balanced translocation for the affected individual
        • BUT- if this individual reproduces, there is a risk to their child of an unbalanced translocation

  • Reciprocal Translocations
    • This occurs as an exchange between two non-homologous chromosomes (is not dependent on the morphology of the chromosome)
    • Again, is fairly harmless to the affected individual (balanced) but they are at risk of producing unbalanced gametes in reproduction
Alternate segregation will produce balanced gametes. Adjacent and 3:1 segregation will produce unbalanced gametes.

Some normal checkpoints/problems in antenatal care

  • Morning sickness
    • Very common, usually occurs in the 1st trimester, usually caused by high circulating levels of βHCG (more common in 1st pregnancy)
    • Can be managed with small, frequent, low calorie meals
      • If problematic, cyclizine may be used
    • Abnormal : Hyperemesis gravidarum
      • Occasionally, mothers are unable to keep fluid and food down due to severe nausea/vomiting.
      • Often in patient management with fluids and anti-emetics is required
      • This is more common in cases with twins (multiple pregnancy) or in trophoblastic disease (both should be investigated)
  • Foetal Movements
    • Normally felt at ~20 weeks (primigravida) or 16-18 weeks (subsequent pregnancies)
  • Lower back pain is common in the third trimester (often worse at night)
    • Treated largely with posture advice and aids to help posture
  • Breast development
    • Breast and nipple enlargement occurs within the first few weeks due to high oestrogen and human placental lactogen
      • this also stimulates GH and insulin production
        • GH stimulates thyroxine production
    • Nipple and areolar darkening can occur ~12 weeks due to increased vascularity and increased melanocyte stimulating hormone production
Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s