Fetal and maternal scanning

• X-ray imaging including CT use is controversial during pregnancy due to potential damage from ionising radiation

  • birth anomalies (teratogenic)
  • increased cancer risk (carcinogenic)
  • germ cell mutation (genetic risk)

  If a woman has had x-ray or CT during pregnancy we can calculate the amount of exposure and usually reassure.
• MRI in pregnancy

  • use of magnets
  • not ionising radiation
  • increasing use
  • e.g. imaging the fetal brain
  • works in absence of amniotic fluid
  • safety in first trimester not yet known
• Ultrasound in pregnancy

  • uses sound waves to create an image
  • no studies found any link to fetal harm
  • main modality for imaging during pregnancy
  • should be used with care, as possible heat and tissue damage can be caused
• The HPA advises that although there is no clear evidence to souvenir scans are harmful to the fetus, parents-to-be must decide for themselves if they wish to have souvenir scans and balance the benefits against the possibility of unconfirmed risks to the unborn child.
• Indications for ultrasound scans in pregnancy

  • diagnosis/management of early pregnancy complications
  • assessment of dates
  • crown rump length/head circumference
  • multiple pregnancy-chorionicity
  • fetal development
  • routine scans 11-14 weeks and 18-21 weeks
  • fetal growth and wellbeing
  • high risk pregnancies
  • 'saving babies lives'
  • guidance of invasive procedures
• Ultrasound - higher frequency (smaller rod) in early pregnancy then progress to larger abdominal ultrasound wand
• Embryo - until 8 weeks post fertilisation
• Fetus - from 8 weeks post fertilisation
• Ultrasound is used preferentially to date a pregnancy rather than relying on parents for LMP or conception date unless they conceived by IVF.
• Crown rump length is used to measure babies in utero until 14+1 weeks (84 mm), after which head circumference is used, this is less accurate as by this point you have variation in baby size.
• Gestation sac > 25 mm without an embryo in it = miscarriage
• crown rump length > 7 mm with no fetal heart pulsations = miscarriage
• ectopic pregnancy

  • +ve pregnancy test
  • no IU gestation sac
  • ectopic seen
• Monochorionic diamniotic pregnancy - identical twins. Higher risk and can get twin-twin transfusion.
• Fetal Anomaly Screening Programme

  • screening for Down's syndrome offered to all eligible pregnant women and takes place between 10 and 20 weeks
  • screening for Edwards and Patau is offered to all eligible pregnant women and takes place between 10 and 14 weeks of pregnancy
  • screening for 11 physical conditions as part of the 20 week scan is offered to all pregnant women and takes place between 18 and 20 weeks of pregnancy. Scans can be completed up to 23 weeks
• Routine 11-14 week scan (optional)

  • incorporates first trimester ultrasound scan
  • fetal heart detection
  • accurate dating
  • detection of major fetal abnormalities
  • chorionicity in multiple pregnancy
  • picture
  • option of trisomy screening
  • combined test - scan and biochemistry
  • quad if >14 weeks - biochemistry only
• The test of choice for both singleton and twin pregnancies is first trimester combined screening. Women can choose which trisomies to screen for, if any.
• Language matters when discussing chromosome abnormalities e.g. 'risk' has negative connotations.
• Combined test

  • ultrasound
  • crown-rump length
  • nuchal translucency
  • maternal serum
  • PAPP-A
  • hCG
  • maternal age
  • smoking status/ethnic origin/maternal weight
• NIPT

  • during pregnancy placenta sheds baby DNA into mother's bloodstream
  • as a result, mother's blood contains a mixture of baby's and mother's DNA
• 20 week ultrasound

  • all pregnant women in England offered scan between 18 to 20 weeks
  • identify anomalies which may indicate the baby might die shortly after birth
  • identify conditions that may benefit from treatment before birth e.g. CDH and open spina bifida
  • help plan delivery in an appropriate hospital/centre
  • help optimise treatment after baby is born
  • timing allows for further diagnostic tests if required and enables women time to consider decisions about continuing their pregnancy
• Anencephaly

  • absence of cortical brain tissue and cranial vault
  • diagnosis usually made antenatally
  • incompatible with life
• Spina Bifida

  • type of neural tube failure to close of varying severity
  • splaying of ossification centres within lower spinal column
  • myelomeningocele
  • option of fetal surgery
• Gastroschisis

  • extra-abdominal herniation of bowel loops through para-umbilical abdominal wall defect
  • no surrounding membrane
• Omphalocele

  • gut herniation via abdominal wall defect
  • covered by a membrane
  • strong association with other fetal anomalies
• Conditions screened for at 20 week scan

  • anencephaly
  • open spina bifida
  • cleft lip
  • diaphragmatic hernia
  • gastroschisis
  • exomphalos
  • serious cardiac anomalies
  • bilateral renal agenesis
  • lethal skeletal dysplasia
  • edwards + patau
• Serious cardiac anomalies

  • transposition of the great arteries
  • atrioventricular septal defect
  • tetralogy of fallot
  • hypoplastic left heart syndrome
• Bilateral renal agenesis

  • no amniotic fluid
  • usually lethal