How Do Ultrasounds Work?

A Window into the Miracle of Life

Pregnancy is an incredible journey, filled with excitement, anticipation, and plenty of questions. One of the most special moments for expecting parents is seeing their baby for the first time. Thanks to modern technology, ultrasounds provide a real-time view of the developing baby, helping to monitor both maternal and fetal health throughout pregnancy.

If you’re curious about how ultrasounds work and what they reveal, this guide will walk you through the science behind them, the different types available, and what to expect during your appointment.

What Is an Ultrasound?1

An ultrasound, or sonogram, is a medical imaging technique that uses sound waves to create pictures of the inside of the body. During pregnancy, ultrasounds allow healthcare providers to visualize the developing baby, track growth, detect abnormalities, and monitor the well-being of both mother and baby.

Unlike X-rays, which use radiation, ultrasounds rely on sound waves, making them a safe, non-invasive, and widely used method for monitoring pregnancy.

Types of Pregnancy Ultrasounds

Different types of ultrasounds serve unique purposes throughout pregnancy:

1. Transabdominal Ultrasound

This is the most common type of ultrasound. A technician applies a gel to the abdomen and moves a handheld device (transducer) over the belly to capture images of the baby. This method is typically used after the first trimester, once the baby is large enough to be seen through the abdominal wall.

2. Transvaginal Ultrasound

Used early in pregnancy, especially in the first trimester, this ultrasound provides a clearer image when the baby is still very small. A small transducer is inserted into the vagina to get a closer view of the uterus. It’s often used to confirm pregnancy, detect ectopic pregnancies, or monitor early fetal development.

3. 3D and 4D Ultrasounds

These advanced ultrasounds provide a detailed, three-dimensional image (3D) or real-time video (4D) of the baby. These ultrasounds are usually more for entertainment and bonding purposes.

When Are Ultrasounds Performed?

Ultrasounds are conducted at different stages of pregnancy to monitor both mother and baby’s health. Here’s a general timeline:

First Trimester (6-13 Weeks)

Confirms pregnancy
Detects heartbeat
Estimates gestational age and due date
Checks for multiple pregnancies (twins, triplets, etc.)
Assesses early fetal development and position

Second Trimester (14-26 Weeks)

The anatomy scan (usually at 18-22 weeks) examines the baby’s organs, limbs, and spine
Measures growth and development
Can reveal the baby’s sex if desired

Third Trimester (27-40 Weeks)

Checks the baby’s growth and position (head-down, breech or transverse)
Monitors placenta health and amniotic fluid levels
Conducted if there are concerns about the baby’s movements or heart rate

What Can an Ultrasound Reveal?

Ultrasounds provide vital insights into pregnancy, including:

✔ Fetal Heartbeat – Verifies that there is fetal cardiac activity which can be visualized at 5 weeks 5 days after the last menstrual period.

✔ Gestational Age – Helps estimate due dates based on baby’s size.

✔ Fetal Growth & Development – Tracks the baby’s growth and development.

✔ Multiple Pregnancies – Identifies if you're expecting twins, triplets, or more.

✔ Baby’s Position – Determines if your baby is head-down for delivery.

✔ Placenta & Amniotic Fluid – Ensures proper function and healthy levels.

✔ Baby’s Sex – Can often be identified around 18-20 weeks.

Source:

Professional, C. C. M. (2025, March 19). Ultrasound in pregnancy. Cleveland Clinic. https://my.clevelandclinic.org/health/diagnostics/9704-ultrasound-in-pregnancy

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