Third Trimester
(Fetal Growth and Welfare Assessment)
The purpose of this examination is to assess:

• Position of the baby
• Size, Growth and Weight
• Amniotic Fluid Volume (amount of fluid surrounding the baby)
• Placental blood flow (Umbilical Artery Doppler)
• Health (Biophysical Profile Score)

Position
Most babies are head down towards the end of pregnancy. Occasionally the baby can be in a breech position,
where the bottom is closest to the cervix (opening to the uterus) or transverse (sideways)

Palpating the abdomen at around 36 weeks will only identify about 30% of babies who are not head first allowing the option of turning the baby (external cephalic version) around 38 weeks or planned caesarean section at 39 weeks. In women who are obese the pick up rate is however even lower.

Failure to identify a non head first baby may lead to an emergency transfer to a Consultant Led Unit in labour for an emergency caesarean section. A scan at 36+ weeks is 100% accurate in determining the position of the baby.

 Size, Growth and Weight
The age of the baby is established in early pregnancy. The size of the baby can be compared with the size expected for this stage of pregnancy, giving information about the baby's growth. An estimate of the weight can be calculated from the measurements.

Recent research has shown that relying on measuring the size of the bump (Symphysis-Fundal Height) is unreliable in detecting small babies who are not growing properly and only picks up 30-50% whereas ultrasound scans will identify about 80-90% of babies with poor growth.

We advise serial growth scans at 24, 28, 32 and 36 weeks for optimal growth surveillance.

Amniotic Fluid Volume (Amount of fluid surrounding the baby)
When baby's are stressed they reduce their blood flow to non-essential organs such as the kidneys to maximise the blood flow to essential organs such as the brain and heart. This reduces the amount of urine they produce and therefore the amount of amniotic fluid surrounding the baby within the pregnancy sac. Low amniotic fluid (oligohydramnios) is therefore sometimes an important sign of a poorly functioning placenta (afterbirth)

Placental blood flow (Umbilical Artery Doppler)
Ultrasound can be used to examine the blood flow in the baby's umbilical cord (Umbilical Artery Doppler Scan). The umbilical cord contains two arteries which carry stale blood to the placenta (afterbirth) and a vein which carries fresh blood back to the baby. Umbilical Artery Doppler Scans give a good guide to how well the placenta is working.

Health (Biophysical Profile Score)
The biophysical profile is a measure of the baby's health and uses ultrasound to examine fetal body movements, breathing movements, tone, amniotic fluid volume and sometimes heart rate variability. This gives an indication of the baby's general wellbeing and identifies babies who are hypoxic (low on oxygen) who may need closer surveillance or delivered early.