Suspected fetal growth restriction or small-for-gestational-age fetus

RCOG GTG 31 (2024); ISUOG practice guidelines

Obstetric ultrasound with biometry, liquor volume and umbilical artery Doppler is the whole assessment. The vetting question is rarely which study, and almost always whether the interval and the Doppler components requested match the degree of concern.

A fetus measuring small on symphysis-fundal height or on a previous scan, or a pregnancy with risk factors for placental insufficiency such as hypertensive disease, previous growth restriction or a positive first-trimester screening pattern.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

Obstetric ultrasound — growth and wellbeing

Obstetric ultrasound

What we'd amend, and why

Biometry with estimated fetal weight, amniotic fluid assessment and umbilical artery Doppler answer the question in one examination. Umbilical artery Doppler is the primary surveillance tool: it identifies the placental insufficiency that separates true growth restriction from constitutional smallness, and the finding of absent or reversed end-diastolic flow escalates surveillance sharply and often brings delivery forward.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayany — Pregnant patients

Decision support only. Local protocol takes precedence.

Worth asking the referrer (1)

None of these hold the request up. They sharpen the protocol or the plan that follows.

What is the gestation, and what were the last biometry and Doppler results and when?
Growth restriction is diagnosed from a trajectory. Without the previous measurements the scan produces a number rather than an answer.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

Pregnant patients

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	Obstetric ultrasound Obstetric ultrasound — growth and wellbeing	Biometry with estimated fetal weight, amniotic fluid assessment and umbilical artery Doppler answer the question in one examination. Umbilical artery Doppler is the primary surveillance tool: it identifies the placental insufficiency that separates true growth restriction from constitutional smallness, and the finding of absent or reversed end-diastolic flow escalates surveillance sharply and often brings delivery forward.
Problem solving	MRI Fetal MRI Fetal — body and placenta	Fetal MRI has no role in assessing growth itself. It is reserved for the structural abnormality that a growth scan uncovers — a body or brain anomaly that ultrasound cannot fully characterise — where the finding changes counselling or the place of delivery.

A markedly abnormal Doppler result is an obstetric emergency conversation, not a report to be filed. The referring team should be told the same day.

Pitfalls

Repeating biometry at short intervals and interpreting measurement variation as a change in growth velocity.
Reporting an estimated fetal weight without the Doppler indices, leaving the referring team unable to distinguish the small-but-well fetus from the compromised one.
Omitting liquor volume, which is a cheap and sensitive marker of placental compromise.
Treating a normal umbilical artery Doppler late in pregnancy as full reassurance; late-onset growth restriction can present with normal umbilical but abnormal cerebral flow, so after about 32 weeks the middle cerebral artery and the cerebroplacental ratio are part of the examination rather than an extra.
Filing absent or reversed end-diastolic flow as a report. It is a same-day conversation with the obstetric team, and at early gestations it is the trigger for ductus venosus surveillance and a delivery decision, not for another scan in a fortnight.

Priors — what to pull first

Retrieve the dating scan: growth cannot be interpreted against uncertain dates, and re-dating late in pregnancy is not valid.
Plot the previous biometry on the same chart and, where available, the customised or population-adjusted centile used locally.

What makes a good request

Estimated fetal weight alone does not distinguish a constitutionally small fetus from a growth-restricted one. Umbilical artery Doppler is what separates them and drives the surveillance interval.
Growth is a trend, so scans repeated too close together produce measurement noise rather than information; an interval of at least two weeks is the usual minimum for biometry, while Doppler can be repeated much more often.
The gestation matters, and it decides which Dopplers answer the question. Before about 32 weeks the umbilical artery is the primary surveillance vessel and, once end-diastolic flow is absent or reversed, ductus venosus Doppler is what informs the timing of delivery. After about 32 weeks the umbilical artery is frequently normal in a genuinely compromised fetus, and it is the middle cerebral artery and the cerebroplacental ratio that detect late-onset disease — so a late growth scan reported on umbilical indices alone has not asked the right question.
Umbilical artery Doppler is not interpretable before around 20 weeks, where absent end-diastolic flow is a normal finding. A growth-restriction request at that gestation is a different conversation — usually about aneuploidy, infection and structural anomaly — and belongs with fetal medicine.

Scoring this once it is done

The classification and risk tools this question ends in.

Estimated Fetal Weight (Hadlock)Barcelona FGR Staging (Figueras & Gratacos)Biophysical Profile (BPP, Manning)Amniotic Fluid Index (AFI) & Single Deepest Pocket Ultrasound Gestational Age & EDD

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

Obstetric ultrasound — growth and wellbeing MRI Fetal — body and placenta

Confirm locally

Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.