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Growth scan in pregnancy and its importance

Dec 09, 2025

Treat every growth scan in pregnancy as answers to three linked questions:
Is the baby growing along a curve?
Is the environment safe (placenta and fluid)?
Is it better to wait or deliver?

Answers to these three questions decide follow-up, therefore timing and care become clear.

What a growth scan is (and what it measures)

A growth scan in pregnancy is an ultrasound that checks the baby’s size and well-being in the second half of pregnancy. It usually includes:

Baby’s measurements: head, tummy, and thigh bone lengths → used to calculate estimated fetal weight (EFW) and a centile for that week of pregnancy.
Amniotic fluid: measured as AFI or deepest vertical pocket, because too little or too much changes plans.
Placenta: location and appearance, so low-lying placenta or signs of poor function are not missed.
Blood flows (Dopplers) when indicated: umbilical artery, middle cerebral artery, and sometimes uterine arteries—because these show how well the placenta is supplying the baby.
Baby’s position and basic well-being: movements, breathing motions; a biophysical profile may be added if needed.

Ultrasound uses sound waves, not radiation; therefore it is considered safe in pregnancy.

When it is usually done (and why the timing matters)

First routine growth check: 28–32 weeks—because differences in growth and fluid become clearer after 28 weeks; therefore the scan can detect babies that are smaller or larger than expected.
Follow-up windows: 32–36 weeks or more often if there is a concern (e.g., diabetes, high blood pressure, twins, previous small baby, less movement reported).
Before birth: a final scan may be used to confirm position (head-down or breech) and to re-check weight and fluid, so delivery planning is accurate.

Teams at BirthRight by Rainbow Hospitals align scan timing with clinical risk and earlier results, because spacing scans correctly shows the trend, not just a single number.

How to read the result (plain meanings, no jargon left unexplained)

1) Is the baby growing along a curve?

EFW on the 10th–90th centile and following a steady path usually reassures; therefore routine care continues.
EFW below the 10th centile suggests small for gestational age; but if the trend is steady and Dopplers and fluid are normal, many babies are simply constitutionally small—so monitoring is increased, not automatically early delivery.
EFW above the 90th centile points to a larger baby; therefore screening for diabetes and later birth-planning discussions are common.

2) Is the environment safe?

Amniotic fluid low (oligohydramnios): may signal placental under-perfusion or membrane leak; therefore Dopplers and closer follow-up are arranged.
Amniotic fluid high (polyhydramnios): can be linked to diabetes or reduced swallowing; so glucose testing and targeted checks are considered.
Placenta low or poorly functioning: increases the chance of growth restriction or bleeding; therefore activity limits, medications (as appropriate), and delivery planning are discussed.

3) Is it better to wait or deliver?

Normal growth + normal fluid + normal Dopplers: wait and re-scan only as per routine, because the balance favours ongoing pregnancy.
Small baby + abnormal Dopplers or falling centiles: intensified surveillance (repeat Dopplers, non-stress tests); therefore delivery may be recommended if oxygen or nutrient flow looks insufficient.
Very large baby: discussion of birth options and timing, because shoulder dystocia risk and induction decisions depend on size and maternal factors.

Why the growth scan changes decisions

It catches growth restriction early, because centiles and Dopplers reveal placental limits; therefore steroids for lung maturity and planned delivery can be timed if needed.
It prevents unnecessary early delivery, because a small-but-healthy pattern with normal Dopplers supports watchful waiting.
It guides diabetes care, so meal plans, medicines, and timing are adjusted when growth is accelerating.
It sets delivery plans (head-down vs breech; placenta not low), therefore birth is safer and logistics are clearer.

Limits to keep in mind (so results are used wisely)

Weight estimates have a margin of error (often around ±10%); therefore trends across scans are more reliable than one value.
Not every problem is visible on ultrasound; so scan results are combined with blood pressure checks, baby’s movements, and lab tests.
Operator and machine quality matter; therefore repeat scans may be suggested if images were limited.

What clinicians may suggest after the scan (typical paths)

All normal: routine visits; repeat scan only if a new concern arises.
Small baby, normal Dopplers: extra scans every 2–3 weeks and movement awareness, because the trend decides timing.
Small baby, abnormal Dopplers or low fluid: closer monitoring (sometimes twice weekly) and planned delivery if placental flow worsens.
Large baby: glucose testing or review, discussion of induction vs expectant management based on estimated size and maternal factors.
Low-lying placenta at 32 weeks: re-scan around 36 weeks, so the final delivery plan is safe.

Conclusion

Use the growth scan to answer three linked questions—growth curve, environment, timing—because that structure separates reassurance from action; therefore care can be tailored without delay or over-treatment. When the scan shows normal size, normal fluid, and normal flow, waiting is usually best; but when size trends slip, fluid falls or rises, or Dopplers change, closer monitoring and planned delivery protect the baby. This is the approach followed at BirthRight by Rainbow Hospitals: clear questions, clear readings, and clear next steps for every growth scan in pregnancy.

FAQs

If my baby is below the 10th centile, does that mean something is wrong?
Not always. Because some babies are constitutionally small, therefore normal Dopplers and normal fluid usually mean closer monitoring rather than early delivery.

Why are Dopplers added to some scans?
They show how well blood flows through the cord, baby’s brain, and sometimes uterine vessels. Because placental limits change these patterns, therefore Dopplers help decide whether to wait or plan delivery.

How does a growth scan affect diabetes or blood-pressure care?
A larger-than-expected baby or extra fluid can point toward diabetes; slowed growth or low fluid can appear with placental strain in hypertension. Therefore meal plans, medicines, and follow-up timing are adjusted to protect growth and oxygen supply.

What should I do if movements feel less but my last scan was normal?
Call your care team. Because scans are a snapshot, therefore new symptoms (reduced movements) still need assessment even after a reassuring report.

Disclaimer: The information above is for general education. It is not medical advice and does not replace an in-person evaluation or your clinician’s recommendations.

Categories

Growth scan in pregnancy and its importance

What a growth scan is (and what it measures)

When it is usually done (and why the timing matters)