Fetal growth restriction

Screening for FGR

Screening can be done clinically or by special investigation. The following methods are used, some of which remain experimental:

• assessment of historical clinical risks
• clinical evaluation of fetal and uterine size
• ultrasound fetal biometry
• umbilical arterial and uterine arterial

Doppler ultrasound

Clinical risk assessment. Evaluate all gravidas for risk factors (TABLE 1). If a woman is determined to be at heightened risk, take appropriate steps to diagnose FGR as early as possible.

Clinical evaluation of fetal and uterine size. Clinical assessment of fetal growth includes estimating fetal size by traditional obstetrical manual examination and by measuring the uterine fundal height.

• Abdominal palpation is inadequate to identify the fetus at increased risk of growth restriction, missing 74% of cases.⁸
• Serial measurements of the uterine fundal height, however, may be more reliable.⁹ This method consists of measuring fundal height from the symphysis pubis using a nonstretchable tape measure and assessing the results against a gestational age-specific nomogram. Limitations include significant interobserver differences and varying effects of maternal weight, parity, and fetal sex. A randomized trial of the method did not demonstrate any benefits, and a subsequent Cochrane review of the same study considered the evidence insufficient for any recommendations.^10,11

Nevertheless, clinical assessment of uterine and fetal size is an essential, inexpensive component of prenatal care and a simple screening tool for identifying mothers who would benefit from further, more definitive sonographic investigation.

Routine ultrasound biometry. The potential benefits of accurately determined gestational age, and recognition of fetal malformations and multiple gestation, via earlyor mid-pregnancy ultrasound are well recognized and justify widespread use.

Routine scanning increases detection of SGA infants.¹² A population-based cohort study¹³ involving over 16,000 singleton pregnancies found that fetuses smaller than expected at mid-second trimester ultrasound (discrepancy exceeding 14 days) were at increased risk for adverse outcomes, including perinatal mortality and SGA.

Unfortunately, these findings have not led to improved outcomes. A high false-positive rate remains a major concern. A prospective observational study¹⁴ found that routine ultrasound did not identify most cases of FGR, but resulted in a fivefold increase in iatrogenic premature delivery and significantly increased neonatal intensive care admissions.

• The Routine Antenatal Diagnostic Imaging with Ultrasound (RADIUS) trial¹⁵ randomized 15,000 low-risk gravidas to routine ultrasound imaging (at 15 to 22 weeks and again at 31 to 35 weeks) or to ultrasound only when indicated. The groups had similar rates of adverse perinatal outcome, distribution of birth weights, and preterm delivery. The trial’s weaknesses include selection criteria for low risk that excluded most pregnancies, inappropriate perinatal-outcome parameters, and suboptimal ultrasonographer expertise.
• A recent Cochrane review¹⁶ of 7 trials involving more than 25,000 women failed to demonstrate any improvements in perinatal mortality and morbidity with routine ultrasound, or any difference in antenatal, obstetric, and neonatal interventions.

Estimated fetal weight may differ from actual weight by as much as 20%.

We also lack evidence regarding longterm outcomes such as neurodevelopment.

Umbilical arterial Doppler. A meta-analysis¹⁷ of 4 randomized trials in unselected or low-risk pregnancies with a total population of 11,375 women found no effect of screening Doppler umbilical artery velocimetry on perinatal death, stillbirth, antenatal hospitalization, obstetric outcome, or perinatal morbidity.

A subsequent meta-analysis¹⁸ of 5 trials of routine Doppler ultrasound in unselected and low-risk pregnancies with a total population of more than 14,000 women also found no benefit for mother or infant.

We lack evidence on long-term outcomes.

Uterine arterial Doppler screening. Increased pulsatility of the uterine arterial Doppler waveform, persistence of the notch, and a significant difference between right and left uterine arteries have been associated with FGR, pregnancy-induced hypertension, and adverse perinatal outcome. A review¹⁹ of 15 studies of routine uterine Doppler in unselected populations showed considerable heterogeneity, but indicated that increased impedance in the uterine arteries identifies about 20% of those who develop FGR, with a positive likelihood ratio of 3.5.

We lack exclusive randomized trials of routine uterine Doppler sonography in unselected and low-risk pregnancies. However, 2 studies done in conjunction with umbilical arterial Doppler found no impact on outcome, and a recent Cochrane review¹⁸ found insufficient evidence to support routine uterine Doppler for FGR screening.

TABLE 1

Risk factors

Identifying FGR in utero

Antepartum diagnosis is based on sonographic measurement of various fetal dimensions.