• Nathan Riley, MD

Obgyno Wino Podcast Episode 9 - Fetal Growth Restriction

"Remember this, for it is as true as true gets: Your body is not a lemon. You are not a machine. The Creator is not a careless mechanic.” - Ina May Gaskin, the mother of authentic midwifery

2016 Central Coast Pinot Noir from Wild Horse Winery and Vineyards (2015 vintage pictured)

PB#227 - Published February 2021 (Replaced PB#204)

Definition of fetal growth restriction

- difficult to report on incidence and prevalence because definitions have varied so greatly over the years

- EFW <10th percentile or abdominal circumference <10th percentile

- SGA (small for gestational age) refers to a newborn weighing <10th percentile

- many issues these definitions; if a fetus has the growth potential to be in the 99%tile and he/she measures to be within the 15%tile, this might be more problematic than a fetus that is constitutionally small but in the 5%tile

- 20% risk of recurrence


- tons of possible etiologies, many of which ultimately result in sub-optimal uterine-placental perfusion and thus inadequate fetal nutrition

Fetal growth restriction (FGR) and Perinatal morbidity and mortality

- FGR increases risk for intrauterine fetal demise (if EFW <10%tile, 1.5% risk of stillbirth, ~2x baseline risk, <5%tile 2.5% risk; more restricted → higher risk)

- increased frequency of neonatal mortality and morbidity if absent or reversed end diastolic flow on umbilical artery Dopplers

- as newborn: increased risk of neonatal morbidity and neonatal death; also cognitive delay in childhood

- higher risk of many chronic diseases in adulthood (obesity, type 2 DM, CAD, stroke)

Complications related to SGA

- hypoglycemia, hyperbilirubinemia, hypothermia, IVH, NEC, seizures, sepsis, RDS, and neonatal death


- fundal heights starting at 24 wga

- a single fundal height measurement at 32-34 wks is 65-85% sensitive and 96% specific for growth restriction

- if fundal height disagrees with predicted GA in weeks by >3, measure EFW by ultrasound

- Hadlock measurements:

  1. Biparietal diameter - outer edge to inner edge of calvarial wall; cross-section should include thalamus and cavum septum pellucidum; no cerebellar hemispheres

  2. Head circumference - same plane as biparietal diameter

  3. Abdominal circumference - cross-section should include stomach, portal sinus, and umbilical vein; no kidneys

  4. Femur length

- Deviation of ultrasound prediction from true fetal weight can be greater than 20% (esp in 3rd trimester)

- If you find EFW or abdominal circumference are <10%tile, evaluate amniotic fluid and perform umbilical artery Dopplers (also look for fetal anomalies)

- If history of FGR in prior pregnancy, it’s worthwhile to investigate possible causes

- Serial growth measurements for these women may be reasonable (though optimal timing intervals have not been established)

- Routine screening for thrombophilias has not been shown to improve outcomes

- Any fetus with growth restriction alone diagnosed at <32 wga OR fetal growth restriction combined with either an additional structural anomaly or polyhydramnios should be referred for genetic counseling and diagnostic testing should be considered


- Sorry...not much here

- Eating more won’t help

- Aspirin hasn’t been shown to be helpful, either


- After FGR is diagnosed, surveillance includes: serial growth, amniotic fluid assessment, and umbilical artery Doppler velocimetry

- UA Dopplers are used to detect impedance within the UA; increased impedance suggests underlying placental insufficiency

- NST or BPP can also be helpful, but generally are important, but don’t start them until fetus reaches a GA at which you would consider delivery (~32 wga)

- as long as everything checks out using these surveillance methods, no need to repeat testing more than q1-2 weeks

- What about Ductus venosus?

>TRUFFLE study found less neurodevelopmental deficiency at age 2 in children affected by FGR who were delivered based on late changes to DV Dopplers compared to delivering based on FHR tracing findings alone

Timing of delivery

- Must take into consideration: etiology, gestational age, and findings on antenatal surveillance

- A kiddo with T18 is less likely to benefit from early delivery than a kiddo with a sick placenta

- Some parents may also forgo early delivery even if it means an increased risk of prenatal mortality (e.g. severe FGR at 25 wga)

- The Growth Restriction Intervention Trial: looked at benefit of delivering fetuses diagnosed with FGR at <34 wga where the obstetrician was unsure was to whether early delivery would be beneficial; babies were either delivered w/in 48 hrs of diagnosis or managed expectantly (close antepartum surveillance until it was felt that delivery should not be delayed)

- BMZ administration was similar

- No significant differences were found in perinatal survival or in the first 12 years of life re: cognitive, motor, language, or behavioral development

- Disproportionate Intrauterine Growth Intervention Trial at Term looked at fetuses diagnosed with FGR at or beyond 36 wga

- Again no differences found

- No adequately powered randomized trials have been completed to determine optimal timing of delivery between 34 and 36 wga

- Eunice Kennedy Shriver NICHHD, SMFM, and ACOG recommend this approach:

  • 38wga - 39.6 wga - Isolated fetal growth restriction

  • 32wga - 37.6 wga - Additional risk factors for bad outcome (e.g. oligo, abnormal Dopplers, maternal risk factors, or comorbidities

  • 32 wga only in most severe cases (e.g. reversed end diastolic flow on UA Dopplers)

Per a 2020 SMFM consult series, further clarification is made by degree of FGR:

  • 38wga - 39 wga: 3rd-8th percentile isolated FGR w/ normal UA dopplers

  • 37wga: <3rd percentile isolated FGR w/ normal UA dopplers

  • Early deliver may be warranted if UA dopplers show absent or reversed end-diastolic flow

  • more info found in CO#764

- Give BMZ if <33.6 wga or <36.6 wga if no previous course, deliver in a facility with NICU; consult MFM if available

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