Prenatal ultrasound scans
This is the first ultrasound in the pregnant female. It is usually performed after 1 to 2 weeks of missed periods.
EARLY PREGNANCY SCAN IS DONE TO:
- See the uterus and the adjoining structures
- To rule any uterine structural malformations.
- To confirm intrauterine pregnancy.
- To rule out ectopic pregnancy.
- For fetal viability assessment.
- To confirm single or multiple (twins or higher order) pregnancies. The best time to assess the same is at early pregnancy scan at around 7-8 weeks
WHEN IS NT scan done?
Done between 11 weeks to 13 weeks and 6 days •when the fetal length (CRL) is between 45mm to 84mm.
WHY IS NT SCAN DONE?
- To accurately date the pregnancy
- To ascertain the growth of developing fetus
- To diagnose multiple pregnancy
- To diagnose major abnormalities like acrania, encephalocele, holoprosencephaly, abdominal wall defect, megacystis, open spina bifida, missing limbs, body stalk anomalies
- Assessment of risk for chromosomal abnormalities. The risk for chromosomal abnormalities in particular Down syndrome (Trisomy 21), Edward syndrome (Trisomy 18) and Patau syndrome (Trismoy 13) is assessed based on the findings of the scan which include the thickness of the skin and the fluid underneath behind the neck (NT), presence or absence of nasal bone, fetal heart rate, blood flow in Ductus Venosus and blood flow in the fetal heart. It is then combined with the maternal serum biochemistry (Double Marker test) to provide improved accuracy for risk assessment.
- To calculate risk for preeclampsia (high blood pressure) and fetal growth restriction (decreased growth of baby)
- To calculate risk for fetal Neural tube defects (NTDs).
- To calculate risk for preterm delivery (delivery before 34 weeks)
WHAT IS THE DURATION OF SCAN?
It takes about 20-30 minutes and depends on the fetal position.
WHEN IS ANOMALY SCAN DONE?
Done at 18 – 20 weeks
WHY IS ANOMALY SCAN DONE?
- All the fetal structures have been formed by this time and develop as the pregnancy advances. In this ultrasound examination is done to assess the fetal growth and to rule out any structural malformations.
- Special attention is paid to the brain, face, spine, heart, stomach, bowel, kidneys and limbs. If any abnormalities are detected the significance of the findings is discussed and the parents are counselled accordingly.
- To determine position of placenta and amount of amniotic fluid surrounding the fetus
- Cervical length measurement.
In case of detection of any structural abnormality in the fetus, further steps can be taken to try and identify the cause and provide counselling about the same.
WHAT IS THE DURATION OF THE SCAN?
It takes about 40-45 minutes for scan. However, it may take longer depending on the baby’s position or until baby moves to a favourable position for scan.
WHEN IS IT DONE?
Fetal growth scan is usually done at 28-36 weeks of pregnancy.
WHY IS IT DONE?
Fetal growth scan is done to evaluate overall wellbeing and health of the fetus.
This scan determines the growth of the fetus by
- Calculation of an estimated fetal weight
- Measurement of the size of the fetal head, abdomen and thigh bone
- Evaluation of the placental position and appearance
- Measurement of the amount of amniotic fluid
- Examination of the movements of the fetus
- Assessment of blood flow to the placenta and fetus by colour Doppler ultrasound.
Doppler study is the study of the blood flows to the fetus.
The decrease in fetal growth (weight) and blood flow (in doppler study) signifies FETAL GROWTH RESTRICTION.
FETAL DOPPLER ULTRASOUND
A Doppler ultrasound is a non-invasive test that can be used to estimate the blood flow through your blood vessels by bouncing high-frequency sound waves (ultrasound) off circulating red blood cells.
It is used to study blood circulation in the baby, uterus and placenta.
FETAL ECHOCARDIOGRAPHY
WHEN IS FETAL ECHOCARDIOGRAPHY DONE?
- It usually performed at 18-24 weeks gestation
- It can also be done early at 13 weeks if necessary.
WHY IS IT DONE?
During nt scan, anomaly scan and fetal wellbeing scan done throughout the pregnancy, the fetal heart and blood vessels are examined.
But specialized fetal echocardiography might be advised for
- Fetus with SUSPECTED CARDIAC ANOMALY (increased nuchal translucency or certain non-cardiac abnormalities detected during the routine scans)
- Women with family history of congenital heart abnormalities/ diabetes mellitus
- Women who are exposed to teratogenic drugs
- Women with history of frequent miscarriage or history of early infancy death in previous pregnancy.
WHAT IS THE DURATION OF THE SCAN?
The scan may take about 40-45 mins. However it may take longer depending on the baby’s position .
WHEN IS IT DONE?
- It is usually carried out at the time of the anomaly scan
- In women with previous preterm birth it can be done as early as 16 weeks
WHY IS IT DONE?
It is done to measure the cervical length and calculate risk for preterm delivery.
Women at high risk for preterm birth, including multiple pregnancies, those with a previous preterm birth, abnormalities of the uterus or previous cervical surgery are recommended this scan over pregnancy duration.