WHAT IS A THIRD TRIMESTER GROWTH AND WELL - BEING?
Ultrasound is performed in the last part of the pregnancy, usually after 28 weeks.
WHY DO WOMEN SOMETIMES FEEL FAINT DURING THIS ULTRASOUND?
As the baby grows in the last part of the pregnancy, the uterus becomes larger and heavier. This faint feeling is due to a fall in blood pressure, caused by compression of the veins that run at the back of the mother's abdomen (the inferior vena cava) by the uterus and baby.
WHY WOULD I NEED A THIRD TRIMESTER ULTRASOUND?
1. ASSESSMENT OF THE BABY'S SIZE AND WELL-BEING
Sometimes your doctor may be concerned that the 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.
2. REVIEW OF THE PLACENTA
Your doctor may wish to review the position of the placenta if there were concerns of a low-lying placenta on your 20-week morphology ultrasound or if you have unexplained vaginal bleeding.
Your doctor may be concerned if you have symptoms such as pain, contractions, vaginal bleeding or reduced fetal movements. A third trimester ultrasound can help provide reassurance that baby is well.
3. REVIEW OF THE BABY'S ANATOMY
Your doctor may wish to review a change, concern or abnormality in the baby, which was noted at your 20-week morphology ultrasound.
You have a twin/multiple pregnancy. Twins are at higher risk of growth problems during the pregnancy. Depending on the type of twin pregnancy, the babies may also be at increased risk of other complications (such as twin to twin transfusion syndrome with monochromic twins).
4. CONCERNS ABOUT THE AMNIOTIC FLUID
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 the baby may be increased above normal (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. The mother and the baby may be checked for other possible problems (for example, polyhydramnios can be associated with gestational diabetes, and oligohydramnios can be associated with small babies).
Serial ultrasounds (more than one ultrasound) are required to assess the growth pattern of the baby over time.
Every baby has its own individual growth pattern, and this can be monitored if there are concerns. Your doctor will usually leave 10-14 days between such ultrasounds to allow more accurate assessment of growth.
5. DOPPLER OR BLOOD FLOW IN THE UMBILICAL CORD
The blood flow in the umbilical artery will be measured. Sometimes, blood flow in the baby’s brain and liver are also checked. Such measurements of blood flow in the baby’s blood vessels are known as Doppler studies.
They help assess the function of the placenta and the well-being of the baby.
For babies who are not growing normally, serial ultrasounds are usually done at intervals of at least 10-14 days. Ultrasounds to review Doppler studies and amniotic fluid volumes can be performed more frequently if required.
It is good for parents to anticipate seeing their growing baby, but not to be too disappointed if this ultrasound proves difficult to understand or the images of baby’s face are impossible to get.