Description
The 11–14 weeks scan, also known as the first-trimester or NT (nuchal translucency) scan, is a crucial ultrasound performed between 11 and 14 weeks of pregnancy. For general practitioners, it provides an opportunity to assess early fetal development, confirm gestational age, and detect multiple pregnancies. One of the key components is measuring the nuchal translucency, which helps screen for chromosomal abnormalities such as Down syndrome. This scan also evaluates the fetal heartbeat, basic anatomy, and placental location, offering valuable information for early pregnancy management.
Summary Listen
- The lecture focuses on the role of a generalist obstetrician/gynecologist in performing 11-13 week pregnancy scans, differentiating their role from general practitioners and fetal medicine specialists. A generalist can handle routine obstetric and gynecological procedures, including normal deliveries and laparoscopies, while a fetal medicine specialist concentrates on detecting fetal malformations. The speaker emphasizes the complementary relationship between generalists and subspecialists.
- Key measurements during the 11-14 week scan include Crown Rump Length (CRL), Femoral Length, Biparietal Diameter (BPD), and Head Circumference. These measurements are crucial for dating the pregnancy and chromosomal analysis. The speaker stresses the accuracy of CRL measurements for gestational age estimation.
- The lecture extensively discusses nuchal translucency (NT) and nasal bone imaging as soft markers for chromosomal abnormalities. Specifics for NT imaging include a sagittal section, proper magnification, and delineation. While older guidelines suggested an NT of less than 3.5mm as normal, newer research indicates a cutoff of 3mm. Nasal bone presence is visualized as an equal sign.
- The speaker addresses common questions regarding absolute NT figures and advises caution, citing recent data suggesting a lower cutoff of 3mm. They also share images of hypoplastic nasal bones and discuss the role of Non-Invasive Prenatal Testing (NIPT) in detecting Trisomy 21, 18, and 13 with high sensitivity and specificity.
- The lecture provides guidance on visualizing fetal anatomy, including the cranium, spine, and palate. Generalists should check the calvarium integrity and identify intracranial translucency to rule out open spina bifida. A continuous palette shadow is ideal, while a discontinuous one should prompt referral to a fetal medicine expert for a 20-week anomaly scan.
- Chest imaging focuses on heart placement, rate, and rhythm. The speaker discusses cytos, diaphragmatic hernias, and renal system imaging, including bladder visibility. Mega-cystis, indicated by a bladder size of 7mm or more, serves as a marker for potential issues and should be noted in lab requests.
- Imaging of the limbs includes the identification of all three segments (thigh, leg, and foot), though limb anomalies can be difficult to detect at this stage. The umbilical cord should be visualized, and the number of vessels identified using color Doppler. Placental imaging should assess size and texture, while noting the potential for placenta accreta spectrum (PAS), especially in patients with prior cesarean sections.
- Cervical length assessment is important for identifying cervical insufficiency and the risk of premature birth. A cervical length of less than 2.5 cm is concerning, especially in patients with risk factors. Uterine artery Doppler is discussed, with a pulsatility index (PI) greater than 1.7 in either artery considered high risk and an indication for low-dose aspirin to prevent pre-eclampsia. The speaker briefly touches upon ductus venosus flow as a contributory marker.
Sample Certificate
About the Speakers
Dr. Pankaj Desai
Consultant Gynecologist, Janani Maternity Hospital, Vadodara, Gujarat
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