Timing of Scans

Timing Of Scans

Scans are useful through a pregnancy to give information about the baby, the placenta and the mother. Scans at different times in the pregnancy give different information.

  • If the pregnancy is inside the uterus (not ectopic)
  • If the baby is alive, especially if there has been vaginal bleeding
  • Dates can be estimated
  • The number of babies present counted
  • If twins are found, whether they are Identical (from one egg) or probably not Identical
  • If other problems such as ovarian cysts are present
  • Information about normal growth and structure of the baby
  • Possible abnormalities
  • The risk of Down syndrome can be refined using measurements on the baby
  • This is an intermediate period in the pregnancy when scanning may give less information
  • Assessment for early growth restriction if “at- risk”
  • Amniocentesis is done at 14 – 16 weeks for checking chromosomal problems such as Down syndrome
  • Fetal morphology, which is looking at the baby to try to detect any abnormalities
  • Checking dates
  • Placental position
  • Cervix length, A short cervix increases the chance of a very premature delivery and recognition of this will assist in measures which help to delay delivery
  • Progress of some problems can be assessed, such as Rh incompatibility and parvovirus infections
  • Bleeding and placental position can be reassessed
  • Reassessment of possible abnormalities seen earlier
  • Placental position
  • Growth rate of the baby
  • Placental function
  • Length of the cervix
  • Baby size
  • Placental function
  • Position of the baby

Scan Information

It may be difficult to detect abnormalities in the baby by ultrasound scans. For example, only about one third of heart defects are found on scans before the baby is born. When the scan is recorded, it may be possible to review the images later and see the defect with the knowledge of what is present. During scanning, evaluation of the scan images is often concentrated on a small portion of the image. Later review of these images may reveal problems that were not seen at the time of the scan. A “normal” scan never guarantees that no defects exist in the baby.


Records & Medicare

Dr Howland keeps selected images backed-up. Some problems not recognised at the time of the scan may be possible to be seen after the baby is born on review of these images when the exact nature of the abnormality is known. Please be aware that abnormalities are missed by all doctors who perform scans due to concentration on small portions of the scan image during examinations and less than ideal scan image quality in some patients.

The Federal Government restricts payments by Medicare to specified conditions before 18 weeks and after 22 weeks. If one of these conditions is not present, the patient will have to pay for the entire scan themselves. Referring doctors should be able to warn patients who do not have a specified condition before the scan is done.

Best Times For Scans

  • Dating: 8 – 11 weeks
  • Early fetal structure and Down risk: 13.0 to 14.0 weeks
  • Detailed structure of whole fetus: 20 – 21.6 weeks
  • Fetal heart: 22 – 25 weeks
  • Birth weight: 36 + weeks
  • Twin to twin transfusion syndrome in identical twins: Fortnightly from 14 to 26 weeks