A guide to what it means when your baby is measuring small — and what we do about it.
Your baby’s estimated weight on ultrasound is below the 10th percentile for this point in pregnancy. This triggers a thorough evaluation — not just more monitoring, but a search for why the baby is small.
Baby is naturally petite — often matching family size. Placenta works normally. Doppler blood flow is healthy. No intervention needed beyond routine care.
Baby is not receiving enough oxygen or nutrients. The placenta, an infection, a chromosomal difference, or an autoimmune condition may be the cause. Requires full workup and close monitoring.
Our first job is to find out which situation applies to you — and if it is true FGR, to understand why.
When a baby is found to be small, ACOG and SMFM recommend a systematic evaluation to identify treatable causes before settling into a monitoring routine.
Comprehensive anatomy survey looking for structural differences that may point to a chromosomal or genetic cause.
Umbilical artery, middle cerebral artery, and uterine artery blood flow to assess placental function.
Blood tests for infections (TORCH panel) and autoimmune conditions that can impair placental blood supply.
ACOG and SMFM recommend offering amniocentesis with chromosomal microarray for growth-restricted babies — particularly when FGR is early-onset (before 32 weeks) or the anatomy scan shows any additional findings.
Chromosomal Microarray
More detailed than standard karyotype. Detects tiny genetic differences (copy number variants) that a regular chromosome count would miss. Found in up to 10% of early-onset FGR cases.
Why It Matters
If a chromosomal condition is found, it explains the growth restriction, guides counseling about prognosis, and changes how aggressively we intervene. Some conditions carry a higher risk of stillbirth at any gestational age.
Amniocentesis is an optional procedure. Your MFM physician will explain the findings that prompted the recommendation, the risk of the procedure (<1 in 500), and what information it can or cannot provide, so you can make an informed choice.
Certain infections acquired during pregnancy can cross the placenta, infect the baby, and cause growth restriction. We screen for these with maternal blood tests and sometimes amniotic fluid testing.
| Infection | How We Test | Note |
|---|---|---|
| CMV (Cytomegalovirus) | Maternal IgM/IgG; amnio PCR if positive | Most common congenital infection causing FGR |
| Toxoplasmosis | Maternal IgM/IgG serology | Linked to raw meat, cat litter exposure |
| Rubella | IgG (usually checked at first OB visit) | Rare since vaccination; causes severe FGR if contracted |
| Syphilis | RPR / VDRL (part of routine prenatal labs) | Treatable; important not to miss |
| Parvovirus B19 | IgM/IgG serology | Can cause fetal anemia and hydrops in addition to FGR |
Some autoimmune conditions cause tiny blood clots in the placenta, cutting off the baby’s nutrient supply. Testing is recommended especially when FGR is early-onset or severe.
A key cause of placenta-mediated FGR. We test for:
• Anticardiolipin antibodies (IgG & IgM)
• Lupus anticoagulant
• Anti-β2 glycoprotein I (IgG & IgM)
Active lupus significantly increases FGR risk. Testing includes:
• ANA (antinuclear antibody)
• Anti-dsDNA
• Anti-SSA / Anti-SSB (Ro/La)
Positive result = actionable — if APS is confirmed, treatment with low-dose aspirin and heparin may be recommended, and monitoring intensity is increased.
Once the evaluation is complete, we set up a structured schedule to watch your baby closely.
| Test | Frequency | What It Tells Us |
|---|---|---|
| Growth Ultrasound | Every 3–4 weeks | Baby’s size and growth velocity |
| Umbilical Artery Doppler | Every 1–2 weeks | Resistance in placental blood flow |
| Middle Cerebral Artery Doppler | Every 1–2 weeks | Whether baby is redirecting blood to the brain (“brain sparing”) |
| Non-Stress Test (NST) | 1–2 times per week | Baby’s heart rate pattern and movement |
| Biophysical Profile (BPP) | As needed | Overall fetal well-being score |
Doppler measures blood flow velocity and direction — it’s our clearest window into how hard the placenta is working.
Carries blood from baby to placenta. Increased resistance means the placenta is under stress. Absent or reversed end-diastolic flow is a critical finding requiring urgent management.
Measures blood flow to the baby’s brain. When the brain gets extra blood at the expense of other organs (“brain sparing”), it signals the baby is compensating for low oxygen.
A deep vessel near the baby’s heart. Abnormal flow here is a late sign of fetal decompensation and often triggers delivery regardless of gestational age.
Timing is guided by ACOG and SMFM guidelines and depends on how the placenta is functioning.
| Clinical Situation | Recommended Timing |
|---|---|
| FGR with normal Doppler, no structural or genetic concerns | 37–38 weeks |
| FGR < 3rd percentile with normal Doppler | 37 weeks |
| Elevated umbilical artery resistance (abnormal but not absent) | 34–37 weeks |
| Absent end-diastolic flow in umbilical artery | 34 weeks |
| Reversed end-diastolic flow or abnormal ductus venosus | 30–34 weeks (individualized) |
| Non-reassuring fetal testing (abnormal NST / BPP) at any gestational age | Immediate evaluation — delivery may be indicated |
We prepare in advance so your baby has the best possible start.
Steroid Injections
Two doses of betamethasone 24 hours apart help the baby’s lungs mature and reduce risk of breathing problems, brain bleeding, and intestinal complications if delivered before 37 weeks.
NICU Coordination
Our team works with neonatology before delivery. If the baby needs intensive care, a NICU team will be present in the delivery room and a bed will be ready.
Continuous Monitoring
Growth-restricted babies require continuous fetal heart rate monitoring during labor. A C-section may be recommended if the baby shows signs of distress.
The most effective intervention is close surveillance and timely delivery guided by your monitoring results.
Write your questions down before each visit. Our team wants to hear them — you are an essential part of your baby’s care team.