The focus of ultrasound during pregnancy will depend on different trimester.
A ) First trimester scan
This is also known as dating scan, viability scan, early pregnancy assessment or early pregnancy scan.
During the first trimester you will need a full urinary bladder or at least partial filled urinary bladder to allowed better image formation.
The medical Sonographer will put some conducting gel on your tummy. Then a small hand-held transducer will be used and rolled over your tummy to get the many views of your baby.
Sometimes you may need a clearer view and the sonographer will used a transvaginal ultrasound probe to capture the image. This is particularly so in the early weeks of pregnancy. Transvaginal ultrasonography is useful if you are overweight or your uterus is very deep in the pelvis (the bladder need to be emptied during the transvaginal ultrasound).
Ultrasound scan is used in early pregnancy to detect the following situation:
Confirmation of pregnancy and it’s location whether intrauterine or extrauterine
Evaluate suspected ectopic pregnancy
Determination of placenta position
Detection of numbers of embryos, pregnancy sac and multiple pregnancies
Assess viability of embryo
Assess gestational age
Detect early pregnancy failure
Diagnose fetal anomalies
Assess fetal growth
Assess associated maternal abnormalities such as ovarian cysts, fibroid
Sometimes, the pregnancy might not implant within the endometrial cavity inside the uterus (mother womb). The ectopic pregnancy implant in the fallopian tube, ovary, abdominal cavity, or cervical region. Subsequently, the ectopic pregnancy will ruptured through the tube and cause bleeding which can be fatal if not detected early.
Transvaginal Ultrasound images of a living embryo in a tubal ectopic pregnancy
Ovarian Ectopic Pregnancy
A Cornual Ectopic Pregnancy (The sac is positioned unfavourably high in the uterus where the fallopian tube joins)
Observations & measurements during first trimester pregnancy
i) Measurement of gestational age by Crown-rump length (CRL)
In order to estimate the fetal gestational age, the Crown-rump length (CRL) of fetal is measured from head to buttock. The CRL is detectable at gestational age of 7 weeks.
Crown-rump length (CRL) of a fetus measured 41.6mm indicated of gestational age at 11 weeks 1 day. The head, body and limbs are clearly seen.
ii) Nuchal Translucency Thickness
The Nuchal Translucency at the back of the neck is due to the edema beneath the skin at the nuchal region (behind fetus neck). This is an important marker to detect abnormality of the fetus such as Down syndrome (trisomy 21), patau syndrome (Trisomy 13), Edward syndrome trisomy 18. The nuchal thickmness should not be more than 3mm.
iii) Nasal bone (NB)
The present or absent of fetal nasal bone is an important marker for aneuploidy (abnormalities in chromosome). The fetus may encounter problem of hypoplastic or absent nasal bone.
Normal nasal bone
iv) Fetal Heart Rate (FHR)
Fetal heart rate measured to ensure baby's heartbeat within normal range.
Fetal heart rate measured in beat per minutes (bpm)
Ultrasonography has become indispensible in the localization of the site of the placenta and determining its lower edges, thus making a diagnosis or an exclusion of placenta previa. Other placental abnormalities in conditions such as diabetes, fetal hydrops,Rh isoimmunization and severe intrauterine growth restriction can also be assessed.
B ) Second trimester scan
C ) Third trimester scan
This is also known as Fetal Well Being Scan
Perform from 24 weeks-to term
To assess baby's position
To assess baby's growth
To assess placenta position
To assess amniotic fluid volume
To perform Doppler studies
This photo shows Colour Doppler on both the normal renal arteries
This photo shows Colour Doppler on normal umbilical cord
Absent of nasal bone
This early pregnancy is detected using transvaginal scan. The fetus is seen as a oblong structure within the gestational sac which is black in colour.
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