Twin growth scans: What Your Team Monitors Over Time

Twin growth scans follow each baby over time. The team looks at individual measurements and how the babies compare with one another, alongside fluid and other findings. The purpose is to identify concerns early enough to review care, not to predict an exact birth weight from one image.

Know which measurement belongs to which baby

Your notes should use consistent labels for the twins across appointments. Ask how the sonographer identifies each baby and how the latest findings relate to the previous scan.

Measurements of different body parts are used to calculate an estimated fetal weight. The word estimated matters. Ask the clinician to interpret the pattern rather than trying to judge a small numerical change on its own.

Ask about each baby as well as the difference

One baby may be smaller than the other. The team considers whether either baby is small for the pregnancy stage and how large the difference is. A size difference is sometimes called discordance.

The importance of that finding depends on the whole assessment. It can lead to more frequent monitoring or a fetal medicine referral. It does not by itself establish twin to twin transfusion syndrome. The shared placenta guide explains why the placental arrangement is another important part of interpretation.

Understand why fluid and Doppler are included

The amount of fluid around each baby provides information in addition to body size. A Doppler examination assesses blood flow in particular vessels and may be added when growth or other findings need closer attention.

Ask what was assessed and whether it changes the next step. A useful question is: “Is the concern about size, the growth pattern, fluid, blood flow or a combination?” You do not need to translate the entire report yourself.

Confirm the next scan interval

With separate placentas, growth monitoring commonly starts at 24 weeks and continues at intervals no longer than four weeks. With a shared placenta, monitoring is more frequent, generally at least every two weeks from 16 weeks. New concerns can shorten the interval.

An abdominal tape measurement does not replace ultrasound monitoring for growth concerns in twins. Our twin care guide explains how scans fit alongside checks of your own health.

Keep symptoms separate from a reassuring result

A scan is useful information about the time it was performed. If you later notice reduced, stopped or concerningly changed movements, contact maternity care immediately, including at night. Do not wait for the next growth scan.

Before leaving, confirm who will explain any outstanding result and whether another appointment or referral has actually been arranged. Keeping the latest report with your notes can help if you are assessed elsewhere.