Why Would I Need a Well Baby Scan?
Not all women need to have an ultrasound in the later part of the pregnancy.

• Assessment of the baby’s size and (well-being):You may be concerned that your baby is too small, not growing well, or too large. Perhaps you have a condition that may affect the growth of the baby, such as high blood pressure or diabetes.
• Review of the placenta: You may wish to review the position of the placenta if there were concerns of a low lying placenta on an earlier scan or if you have unexplained vaginal bleeding. Most women with a low-lying placenta seen at 18-20 weeks will not have a problem by the time they get to the third trimester. As the uterus gets bigger, it tends to pull the placenta up and away from the cervix.
• You may have symptoms such as pain, contractions, vaginal bleeding or reduced fetal movements. A well baby ultrasound can help provide reassurance that baby is okay.
  
• Review of the baby’s anatomy: You may wish to review a change, concern or abnormality in your baby which was noted on an earlier ultrasound examination.
• Assess the position of the baby: You may be curious about the position of the baby (for example, if baby is lying in a transverse position). This becomes more important towards the end of the pregnancy when the delivery of the baby gets closer.
• You have a twin/multiple pregnancy: Twins are at higher risk of growth problems during the pregnancy. Depending on the type of twin pregnancy, your babies may also be at an increased risk of other complications and you may just want to be reassured that all is well.

What Will Be Assessed On a Well Baby Scan:

Measurements of the baby:

A well baby ultrasound scan will commonly measure:

• baby’s head – biparietal diameter (BPD) and head circumference (HC).
• baby’s abdomen – abdominal circumference (AC).
• baby’s leg – femur length (FL).

Each measurement is compared to a normal reference range, which varies with gestation. Every individual baby has its own characteristics (for example, some babies have bigger head measurements or shorter femur measurements). These characteristics are often similar to the baby’s parents (for example, one parent may have a big head or short legs).

Measurements outside the normal range are not always significant, especially if the difference is minimal. Your baby will be carefully assessed and additional measurements taken if there are concerns about significant deviations from normal.

Head, abdominal and femur measurements are combined in a special formula to estimate the weight of your baby.

The size of the baby (the estimated fetal weight):
The estimated fetal weight (EFW) is compared to the size of other babies at the same gestation.
This is often expressed as a percentile:

• An EFW on the 50th percentile is an average sized baby.
• An EFW less than the 10th percentile is a small baby.
• An EFW more than the 90th percentile is a big baby

This ultrasound weight is an estimation of your baby’s size only – there is a recognized 15% error in this estimation, with your baby being either 15% smaller or 15% larger than the estimated weight. While we recognize there is this error present in our estimation of your baby’s size, ultrasound remains the best way your doctor has of checking the size of your baby.

Every baby has its own individual growth pattern, and this can be monitored if there are concerns.

The amount of amniotic fluid around your baby:
The amount of amniotic fluid or liquor is usually expressed as an “amniotic fluid index” (AFI). This index is calculated by measuring the maximal vertical distance of fluid in each quadrant (or corner) of the pregnancy sac. There is a wide range for the normal volume of amniotic fluid in a pregnancy, and this range will vary with gestation.

Sometimes, the volume of fluid around your baby may be increased (polyhydramnios), or perhaps the volume of fluid around your baby is below the normal range (oligohydramnios). Changes in the fluid volume are not always significant, especially if the difference is minimal. If the fluid level is low you may be required to rest.

The blood flow in the umbilical cord (the umbilical artery):
The blood flow in the umbilical artery (which is in the baby’s umbilical cord) will be measured and is known as an umbilical artery Doppler.This may help assess the function of the placenta and the health, welfare and well-being of your baby. This measurement is usually expressed as a resistance index (RI). Babies that are not growing normally (known as growth restricted) may show progressive changes in the resistance of this artery. Changes in this measurement is not always significant, especially if the difference is minimal.

The baby’s heart rate and rhythm:
Your baby’s heart rate will vary, just as it does in adults. Most babies have a heart rate between 120-180 beats per minute.

The position of the baby:
This ultrasound will tell us what position the baby is lying in:

• Head down (cephalic).
• Bottom down, with the head at the top of the uterus (breech).
• Sideways, across the uterus (transverse).

The position of the baby is more important towards the end of the pregnancy, when the baby is due for delivery.

The position of the placenta:
Your health care provider will want to know that the lowest edge (inferior margin) of the placenta is not lying too close to the cervix. This is known as placenta praevia or a low-lying placenta.
Transvaginal ultrasound may be required during your third trimester ultrasound if there are concerns about the position of the placenta, to get a better look at the cervix area and lower edge of the placenta.

The anatomy of the baby:
As your baby grows during the pregnancy, it fills up the space inside the uterus, pressing its body against the wall of the uterus. This means some parts of the baby may be more difficult to see later in the pregnancy, especially hands and feet. The baby’s position will also affect how well some structures are seen, including the heart, face, and spine.

Some of the structures which we try to routinely review in a well baby ultrasound include the baby’s kidneys, bladder and face.

The length of the cervix:
This is especially important if you have premature labour, vaginal bleeding or pain. The length of the cervix is not as important for us to know as you get closer to your due date (full term).
Sometimes a transvaginal ultrasound may be required to get a better view of the cervix.