About Your Scans

During pregnancy, the majority of women and their partners look forward to the scans. It is a chance to see your baby and it gives you both a chance to start bonding with your baby too.

About your scans

Early Pregnancy Scans (before 12 weeks of pregnancy)

These are often performed as an internal scan using a vaginal probe. You will need to have an empty bladder for these.

They are usually performed for one of the following reasons:

  • Early pregnancy bleeding (also termed as a “Threatened Miscarriage”)
  • If you have had a previous ectopic pregnancy
  • If you have significant vomiting during pregnancy (this is reserved for women who require hospitalisation due to excessive vomiting)
  • If you have significant pain

Scans in early pregnancy are not usually performed for reassurance or for dating unless agreed with a consultant at the unit where you are due to book. This is due to a high demand for the use of the service.

1st Trimester Screening Scan (also known as the Nuchal scan)

This is performed at approximately 12 weeks of pregnancy. The aim is to check for any major problems with baby and to measure the thickness of the fluid at the back of your baby’s neck. This measurement will be combined with blood test results to give you a risk of your baby being affected by either Downs Syndrome or similar genetic problems.

It is important to note that a low risk does not give you the ‘all clear’ and that a high risk does not mean that your baby is affected. It just gives you the chance to get further tests if need be.

The aim of these scans (as with all screening tests) is to diagnose women whose babies are at a high risk of Downs Syndrome and other similar problems, allowing them the opportunity to have amniocentesis for a formal diagnosis. If that is positive, they will be given the offer to terminate the pregnancy.

Some people would never consider a termination for moral, ethical or religious reasons. If this is the case, you should think carefully before embarking on more invasive tests as they carry a risk of miscarriage.

The Anomaly Scan

This is performed at approximately 20 weeks of pregnancy. By this time the baby is a lot larger and more of the internal structure can be seen more clearly. This enables the sonographer to look at your baby in a lot more detail. Your baby will be checked from head to toe and lots of different organs measured (even bits of the body you never knew existed!) The site of the placenta will also be checked as will the fluid level.

If there are any issues or if something cannot be seen clearly, then you will be invited back for a further scan. If the person scanning you is worried, they may ask for a more senior opinion on the same day or refer you to a specialist unit.

Later Scans

These can be performed for growth, fluid level, blood flow or the site of the placenta.

Scans for growth, fluid level and blood flow may be performed if:

  • Your doctor feels that your baby is too small for your dates
  • Your baby’s growth requires monitoring, especially if you previously had a small baby
  • You have other medical conditions, for example Pre-Eclampsia or Diabetes
  • You have twins or triplets (or more)
  • Your placenta was low at your 20 week scan


It is difficult to assess the growth of a baby from one scan alone. All you can tell is that the baby is small, medium or large. To check the growth rate of a baby, two scans need to be performed 2 weeks apart.

Fluid level

Also known as the ‘Liquor’, this again can be low, normal or high. Low levels are seen in women whose waters have gone early or if their babies are not producing enough fluid. High levels are most commonly seen in diabetic women, but can also be seen in normal pregnancy and some other unusual conditions.

Blood Flow

Also known as the ‘Dopplers’. This measures the blood flow in the baby’s cord. It gives a good indication as to how well baby is.

Estimated Fetal Weight

Some women get quite worried by the estimated weight given in scans. The important word in the phrase is “Estimated”. The smaller a baby is, the more accurate the estimated weights are.

Towards the end of pregnancy, the estimated weights are accurate to within 17.5%. This is not accurate at all. This could mean that a baby estimated at 8 pounds, could weigh anywhere between 6½ pounds and 9½ pounds. This is why scanning for large babies towards the end of pregnancy is often unhelpful.

Placental Site

If your placenta was low at the 20 week scan, the scan will be repeated at 32 weeks. By this time, most placentae will be clear of the cervix and therefore not low any more. If it is still low, you will probably get a further scan at 36 weeks to recheck and make a plan for delivery.

Special Circumstances

If you have a low placenta and have had a caesarean section for a previous delivery, then this can be a problem, especially if the placenta is on the front of the womb. The problem happens because this is where the caesarean scar is on the womb. If this is the case, then further tests should be performed to see if the placenta has attached too firmly to the womb and in some circumstances, it can go through the womb itself. This is not common after one caesarean section but the risk increases significantly in women who have had two or more caesarean’s.