The document summarizes a third trimester ultrasound examination performed between 28-32 weeks of gestation. A third trimester ultrasound assesses fetal growth and anatomy, amniotic fluid levels, and placental position. It measures fetal size, heart rate, and blood flow. It also checks cervical length and fetal position. The goal is to monitor fetal well-being and check for any issues like placental problems or abnormal growth. The ultrasound is performed transabdominally with a full bladder or transvaginally if needed for a clear view. It provides important information to monitor the health of the mother and fetus late in pregnancy.

1. Ultrasound examination
of third-trimester of
pregnancy
Presented by
Mohamed Gamal Khattab

2. THIRD TRIMESTER
A third trimester ultrasound is performed in the last part of the
pregnancy, usually performed between the 28th and 32nd week of
gestation.
The ultrasound scan isn’t 100 percent accurate, but the
advantages of the test are that it’s non-invasive, painless and safe
for both mother and unborn baby.
The fetus has grown to approximately 15 inches in length and
1000 to 1400 g in weight by the beginning of the third trimester.
Lungs, organs, and vessels are maturing in preparation for birth.

3. HOW IS A THIRD TRIMESTER ULTRASOUND
PERFORMED?
• The procedure depends on the type of ultrasound used,
but may include:
1-Transabdominal ultrasound involves
scanning through your lower abdomen.
 The sonographer uses your full bladder as
a ‘porthole’ to your uterus.
 The scan usually takes about 30 minutes.

4. 2-Transvaginal ultrasound involves scanning with the
ultrasound probe lying in the vagina.
 a transabdominal ultrasound can’t produce clear enough pictures.
There may be too much air in your bowel.
 This may be to check for a low lying placenta,
to look at the length of the cervix .
 less discomfort but it is safe and will
not harm either you or your baby.

5. DO I NEED A FULL BLADDER FOR THIS
ULTRASOUND?
 We usually get better images during transabdominal ultrasound if
the bladder is partially filled.
 A full bladder moves bowel out from the pelvis into the abdomen,
helping visualisation of the pregnancy, uterus and cervix.
 ask you to drink water prior to the assessment. Please empty your
bladder 1 hour before your appointment, drink 1-2 glasses of
water and try not to empty your bladder again until after your
appointment.
 You will need to empty your bladder before the transvaginal
ultrasound begins .

6. 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.
 Please tell the sonographer if you begin to feel faint or nauseous at
all during your scan.
 Your position can be changed before you feel worse - lying more
on your side or more upright will usually help resolve your
symptoms.

7. WHY A THIRD TRIMESTER ULTRASOUND?
1. Assessment of the baby’s size and welfare (well-being) - your baby
is too small, not growing well, or too large.
2. Review of the placenta- to review the position of the placenta ( a low
lying placenta on your 18-20 week) or if you have unexplained vaginal
bleeding.
3. symptoms such as pain, contractions, vaginal bleeding or reduced fetal
movements
4. Review of the baby’s anatomy
5. Assess the position of the baby- (f baby is lying in a breech position).
6. You have a twin/multiple pregnancy. Twins are at higher risk of
growth problems during the pregnancy. (twin to twin transfusion syndrome
with monochorionic twins)

8. WHAT WILL USUALLY BE CHECKED AT A THIRD-TRIMESTER
ULTRASOUND?
1. Measurements of the baby
2. The size of the baby (the estimated fetal weight)
3. The amount of amniotic fluid around your baby
4. The blood flow in the umbilical cord (the umbilical artery).
5. The baby’s heart rate and rhythm
6. The position of the baby.
7. The position of the placenta.
8. The anatomy of the baby.
9. The length of the cervix.
10. The uterus
11. 3D/4D images of your baby.

9. 1-Measurements of the baby
The third trimester ultrasound 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.
• These head, abdominal and femur measurements are
combined in a special formula to estimate the weight of your
baby.

12. 2-The size of the baby (the estimated fetal
weight)
 The estimated fetal weight 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.

13. 3-The amount of amniotic fluid around your
baby.
 This amount of fluid is
usually expressed as the
“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.

14. 4-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.
 Sometimes blood flow in the
baby’s brain (the middle cerebral
artery) and liver (the ductus
venosus) are also checked.
 Such measurements of blood flow
in the baby’s blood vessels are
known as doppler studies.

15. 5-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.
6-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.

16. 7-The position of the baby.
Cephalic or Vertex
• Fetal head lies most inferior, closest to the cervical os.
 Transverse
• Fetal head and body lie across the maternal abdomen.
• Check for signs of placenta previa.
 Oblique
• Fetal head and body are lying at a 45° angle to the maternal sagittal plane.
• Document location of the fetal head
 Breech
• Fetal head is located in the superior portion of the uterus.
• Presenting part should be determined after 36 weeks’ gestation.

17. Breech-Baby-Ultrasound

18. 8-The position of the placenta
 Your doctor 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.

20. 9-The uterus
 The uterus is checked for problems such as uterine fibroids.
10-3D/4D images of your baby
 We aim to obtain good 3D/4D pictures of the baby’s face, but we
also think it is important to make sure that your baby is
otherwise healthy and growing well.
 usually done after the baby has been fully examined with all
routine measurements and other images completed
 The best time to obtain 3D/4D images of baby is between 24 and
34 weeks.

22. FETAL WELL-BEING

23. Third and final ultrasound video at
37-week pregnancy

24. Thank You