Ultrasound Obstetrics

An obstetric ultrasound is a noninvasive imaging test that uses high‑frequency sound waves to visualize the uterus, placenta and developing fetus. It assesses gestational age, fetal growth and anatomy, placental position, amniotic fluid volume and multiple pregnancies, and can guide diagnostic or therapeutic procedures. Performed transabdominally or transvaginally, it’s routinely used in antenatal care to monitor fetal health and development with no known long‑term risks.

Routine obstetric ultrasound timing: a dating/viability scan is usually done around 8–14 weeks (earlier viability scans at 6–7 weeks if needed). Nuchal translucency is assessed about 11–13+6 weeks. The detailed anatomy (anomaly) scan occurs around 18–22 weeks. Additional growth and placental scans may be scheduled in the third trimester (roughly 28–40 weeks) if indicated.

Obstetric ultrasound can often reveal a fetus’s biological sex by visualizing external genitalia, typically from about 16 weeks and most reliably during the 18–20-week anatomy scan. Accuracy depends on fetal position, gestational age, equipment quality and operator experience, so it’s not 100% certain. Ultrasound identifies physical sex features, not a child’s future gender identity; some clinics may decline to disclose.

To prepare for an obstetric ultrasound, wear loose clothing and bring previous scans and ID. For early pregnancy scans, drink 500–750 mL water about an hour before and avoid voiding so the bladder is full; for transvaginal scans empty your bladder. Continue usual medications and eat normally unless instructed otherwise. Arrive on time and follow any specific clinic instructions.

An obstetric ultrasound typically takes 20–30 minutes for a routine dating or growth scan. Early viability scans may be shorter (10–15 minutes), while detailed anatomy or anomaly scans often require 30–45 minutes. Time can be longer if positioning, fetal movement, or extra measurements/Doppler are needed, and arrival, consent, or technician discussion add additional appointment time.

The four common pregnancy scans are: 1) Dating scan (about 8–14 weeks) to confirm pregnancy, number and estimated due date; 2) First‑trimester screening/nuchal translucency (11–14 weeks) to assess chromosomal risk; 3) Anatomy/anomaly scan (around 18–22 weeks) to examine fetal organs and structure; 4) Growth/third‑trimester scan (after 28 weeks) to monitor growth, position and wellbeing.