First Trimester Ultrasound: The Importance of Pregnancy Check-ups at 11–13 Weeks

A pregnancy ultrasound examination during the first trimester, particularly between 11 weeks and 13 weeks and 6 days, is not simply a routine ultrasound to view the fetus. Medically, this examination is known as First Trimester Screening (FTS) or NT Scan, and it plays a crucial role in early detection of potential abnormalities.

The FTS examination helps doctors assess the early development of the fetus, the risk of chromosomal abnormalities, and the potential for future pregnancy complications.

What is Assessed in a First Trimester Ultrasound?

During this golden period, the doctor will conduct detailed screening of the fetus's fine anatomical structures and genetic markers (soft markers), including:

1. Main Parameters Checked

In this time window, the doctor performs screening for fine anatomical structures and genetic markers (soft markers):

• Nuchal Translucency (NT) : A measurement of the thickness of the fluid at the back of the fetus's neck. Excessive fluid accumulation (>3.5 mm) is closely associated with the risk of chromosomal abnormalities or congenital heart defects.

• Nasal Bone : Fetuses with Down Syndrome often have an absent nasal bone in the first trimester.
• Ductus Venosus & Tricuspid Regurgitation : Assesses blood flow in the heart and hepatic vessels to detect the risk of primary heart defects.
• Basic Anatomy : Ensures the skull is intact (ossification), the presence of an abdominal wall, and completeness of the extremities (hands and feet).

2. Disorders that can be screened

This examination is able to detect or provide high-risk signals for the following conditions:

• Aneuploidy (Chromosomal Abnormalities): Especially Trisomy 21 (Down Syndrome), Trisomy 18 (Edwards Syndrome), and Trisomy 13 (Patau Syndrome).
• Congenital Heart Defects: Thick NT despite normal chromosomes is often an early indicator of structural heart problems.
• Abdominal Wall Defects: Such as Omphalocele or Gastroschisis .
• Central Nervous System Disorders: Such as Anencephaly (absence of a skull) which can be clearly seen at this age.
• Preeclampsia Risk: By measuring the mother's uterine artery blood flow, doctors can predict the risk of hypertension in future pregnancies.

3. Relationship with NIPT: Which is Superior?

Many parents are confused about choosing between FTS ultrasound and NIPT (Non-Invasive Prenatal Testing), which uses maternal blood samples. Both are complementary, not substitutes:

The situation: Ideally, patients should have both. If funds are limited, a FTS ultrasound is a "must-have scan" because the NIPT cannot determine whether the fetus has complete hands or a complete skull.

4. Recommendations

• Complementary : It should be reiterated that NIPT is not a substitute for first-trimester ultrasound, although it is more accurate for chromosome assessment. This is because only FTS ultrasound can detect suspected physical defects and screen for preeclampsia risk.
• Stepwise strategy : A FTS ultrasound is recommended first. If the results indicate a risk, NIPT is performed as a follow-up step before deciding on an invasive procedure.
• Limitations : NIPT cannot detect open neural tube defects (NEDs). This condition must still be monitored via ultrasound.

5. Examiner Competence and Services at EMC Pekayon Hospital

The FTS examination relies heavily on operator precision because it measures details in millimeters. Therefore, this examination must be performed by medical personnel with specific competencies and certifications.

Good news for patients, EMC Pekayon Hospital now has an obstetrician and gynecologist (Sp.OG) who holds International Board Certification specifically to conduct FTS examinations.

This article was written by Dr. Probo Mangastomo, SpOG, FICS, Int. Aff. RANZCOG (Obstetrics and Gynecology Specialist at EMC Pekayon Hospital).