Ultrasonography scans in pregnancy serve several purposes. There are typically two recommended scans: the 11-14 week NT scan to screen for anomalies and the 18-22 week anomaly scan. Additional scans may be needed depending on risk factors and medical history. The NT scan screens for conditions like Down syndrome while the anomaly scan checks for structural abnormalities. Follow-up scans later in pregnancy monitor growth, check high-risk conditions like preeclampsia, and assess fetal well-being. Ultrasound is a valuable screening tool when used appropriately during pregnancy.

1. ULTRASONOGRAPHY SCANS
IN PREGNANCY
HOW MANY? WHEN? WHY?
Dr. Nisheeth M. Oza

2. Dr. Nisheeth M. Oza
M.D., D.G.O., F.C.P.S., D.N.B., (M.N.A.M.S.) (OBGYN)
D.A., M.B.B.S., Dip. YAN
Obstetrician, Gynaecologist, Infertility Consultant,
FMF Certified Ultrasonographer (FMF ID 145907)
Licensed for Aneuploidy Screening NT, NB, DV, Cervix & PIH Screening.
Diploma in Yoga, Ayurveda & Naturopathy
Dr. Oza’s Hospital 87/7, Panvel 410206, Maharashtra India.
Email : drnmozas@gmail.com
Website : drozashospital.com
YouTube : DrOzaConnects

3. What is a Screening Test?
• A test offered to entire apparently healthy population to
identify individuals at sufficient risk of a specific disorder to
provide them with required counseling & care.
• An Ideal Screening Test should be Sensitive, Specific, Simple,
Affordable, Safe, Non-invasive, well-accepted, Widely
available, repeatable (reproducible).
• Ultrasonography satisfies most of the criteria of an Ideal
Screening Tool in Pregnancy.

4. HOW MANY SCANS IN PREGNANCY ?
• There is Consensus about two scans :
1] 11 to 14 weeks’ scan, also known as NT Scan.
2] 18 to 22 weeks’ scan, also known as Anomaly Scan.
DOES IT MEAN THAT THESE ARE THE ONLY TWO SCANS WE SHOULD BE
DOING?
NO, Besides these, scans may be advised depending upon the
indication directed by history, examination or individual risk factor.
In 1st Trimester : about 20% of pregnant women may require scan.
In early Third Trimester : about 20% of pregnant women may require
scan.
In late Third Trimester : about 15% of pregnant women may require a
scan.

5. FIRST TRIMESTER say 6 to 9 weeks:
HISTORY OR EXAMINATION DIRECTED SCANS
1 out of 6 pregnancies may end up in miscarriage.
• H/o Bleeding – look for viability.
1 out of 100 Pregnancies may be Ectopic (Incidence 0.25 – 2 %).
• H/o Bleeding & Pain – Rule out Ectopic Pregnancies.
• In women who have conceived with ovulation induction medication
or with ART i.e Artificial Reproductive Techniques, look for Twin
Pregnancy & determine Chorionicity, which is important for
management & prognostication.

6. 11-13.6 WEEKS SCAN – NT SCAN
PURPOSE :
• To screen for Aneuploidy : Trisomy 21, 18, 13.
• To screen for likelihood of developing Pre-eclampsia.
• To screen for likelihood of developing FGR – Fetal Growth Restriction.
• First assessment of length of Cervix.
• Early detection of Certain Anomalies in Fetus.

7. PRE-TEST COUNSELING :
• What is Aneuploidy?
Deviation from normal chromosome makeup, be it in number or in
structure.
• What is Trisomy?
Presence of an extra Chromosome at a particular pair of
chromosome at a particular pair of chromosome. eg. In Trisomy 21,
the no. 21 chromosome has 3 chromosomes instead of normal 2
chromosomes.

8. • Before doing the scan , Data is fed from the History, like
- Mother’s age
- Race
- Previous number of Children
- Previous Miscarriages
- Prior Aneuploidy
- History of smoking
- Maternal Diabetes Mellitus
- IVF Conception
• Then ultrasonography is performed by a trained preferably FMF certified
sonographer. It may take 15-30 minutes, sometimes longer, till proper
required views & images are obtained. NT is measured in proper Mid-
sagittal Scan. Other parameters are also looked for & measured.
Eg. NB, DV, TR, Cx (TVS), Uterine Artery Doppler (PI).

9. • Data is uploaded in FMF licensed software to calculate risk – It will
give us Post Test Risk.
She is also offered Serum Biochemistry i.e. Double Marker Test to
improve the detection rate of Trisomy.
• If she undertakes Double Marker Blood Test, the Laboratory gives us
risk from combined Tests i.e. NT & Double Marker Test.
- Detection rate from NT Scan is 80%.
- Detection rate from combined Test is 90%.
In selected cases NIPS may be preferred, which is costly & has its own
advantages and limitations.

10. POST-TEST COUNSELING
Now the couple is counseled about Post Test Risk,
• If she is low risk, she is reassured.
• If she is at High risk for Trisomy, she is counseled and offered
Definitive Diagnostic Invasive Test to confirm.
• If she is at high risk for developing Pre-eclampsia or FGR, she is
offered low dose Aspirin 150 mg/day from 13th week till 34 weeks of
pregnancy.
• If she has short cervix on TVS Scan, cervix length < 25 mm, or if her
previous history is suggestive of incompetent cervix, she is offered
Cervical Cerclage i.e. Tightening of Os Operation.

11. • If congenital fetal anomaly is detected, such as
- Anencephaly (Absence of Forebrain)
- Acrania (Absence of Skull)
- Omphalocoele
- Gastroschisis
- Megacystis
Couple is counseled regarding the condition, its prognosis & the
condition is managed as per couples decision.

12. 18 – 22 WEEKS’ ANOMALY SCAN
• Incidence of Congenital Anomalies in general population is around 2%
(range 1.5 – 3 %).
• Ultrasonography can detect many (though not all) of major structural
congenital anomalies of fetus, between 18 & 22 weeks.
• Risk factors for Congenital Anomaly, may be – Maternal Diabetes
Mellitus, Infection, Exposure to Teratogen.
• Remember friends, 80-90% of Congenital Anomalies occur in fetus
without risk factors.
• Systematic Examination of anatomy of fetus is carried out, to detect
structural anomaly and/or soft marker for genetic abnormalities.

13. ESSENTIAL ELEMENTS OF FETAL ANATOMIC SUEVEY
• Head & Neck
• Face
• Chest
• Heart
• Abdomen
• Spine
• Extremities – all four.
SOFT MARKERS : eg. Nuchal Fold Thickness.
Sonographer keeps a checklist & sees the anatomy & looks for the
markers.

14. FACTORS WHICH INFLUENCE DETECTION OF ANOMALIES
• Operator’s experience, skill, training.
• Resolution of equipment.
• Sufficient time allocated for the scan.
• Type of malformation – Major vs Minor, Single vs Multiple.
Natural history of the disease during fetal life.
• Gestational age at ultrasound examination.
• Length & accuracy of follow up after birth.

15. 22 -24 WEEKS’ FETAL ECHOCARDIOGRAPHY
• In fetus at high risk of congenital heart anomaly.
• When congenital heart anomaly is suspected in anomaly scan at 18 -
20 weeks.
Prevalence of GDM in pregnancy : 1.3 - 18 % in different parts of India.
Prevalence of FGR : 3 – 7%
Prevalence of Pre-eclampsia : 5 -17 %
Prevalence of Chronic HT : 2 – 3%

16. AT 28 – 32 WEEKS’ : GROWTH SCAN
It may be required in say 20% of pregnant women :
• If Symphysis Pubis – Fundal Height is less than period of gestation & Doctor
suspects FGR.
• In high risk cases, eg.
- Pre-eclampsia.
- Gestational Diabetes Mellitus.
- Twin Conception.
- Previous unexplained Stillbirth.
- Low lying placenta.
• In an affected FGR fetus, the scan may be required to be repeated
depending upon the situation.

17. AT 36 -38 WEEKS FOR BIOPHYSICAL PROFILE, OBSTETERIC
COLOUR DOPPLER
It may be required in 15% of pregnant women.
• In High Risk Cases eg. Pre-eclampsia, Gestational Diabetes Mellitus,
FGR.
• Previous Unexplained Stillbirth.
• Scar Thickness in case of previous LSCS.

18. Remember 3 things :
1) Ultrasonography is an ideal screening tool in pregnancy. One should
use it at correct GA, for correct indication in the correct manner.
2) NT Scan & Anomaly Scan are the two ‘must’ Scans for you.
3) In other 20% of cases, additional scans may be indicated depending
upon the History, Examination or Risk Factor.

19. Thank You