Fetal growth restriction: Clinical sciences

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Introduction 0:00–0:48

Fetal growth restriction, or FGR, is also known as intrauterine growth restriction, or IUGR; and is defined as a fetal weight or abdominal circumference below the 10th percentile for gestational age, as determined by ultrasound measurements.
In contrast, small for gestational age, or SGA, refers to a term newborn with a birth weight less than the 10th percentile for gestational age.
FGR can result from a variety of maternal, placental and fetal conditions. It requires increased antenatal surveillance, possibly early delivery, and it contributes to poor perinatal outcomes and negative long-term health impacts for the child.When a patient presents with a chief concern suggesting fetal growth restriction, your first step is to perform a focused history and physical examination.

Diagnosis 0:48–4:30

Key findings on history include prior delivery of an SGA infant, multiple gestation in the current pregnancy, and inadequate maternal weight gain with or without a maternal malabsorptive syndrome.
Other risk factors include an intrauterine infection like cytomegalovirus, toxoplasmosis, rubella, or varicella zoster; maternal chronic disorders with a vascular component such as chronic hypertension, long-standing, poorly controlled diabetes, or chronic kidney disease; or a history of antiphospholipid syndrome, also known as APS Here’s a clinical pearl!
Acquired thrombophilias such as APS can contribute to FGR, but inherited thrombophilias do not. Finally, be sure to ask about any substance use during pregnancy, like tobacco or alcohol, as well as teratogen exposure, including medications like valproic acid, cyclophosphamide, and warfarin.On physical examination, note your patient’s weight and ensure adequate weight gain.
Beginning at 24 weeks, measure the fundal height and note whether it is appropriate for the gestational age, by measuring from the top of the pubic symphysis to the fundus of the uterus using a flexible measuring tape.
The measurement should approximate the gestational age in weeks, plus or minus 3 centimeters. While fundal height is a useful screening tool for FGR, keep in mind that obtaining an accurate measurement can be difficult in the presence of adiposity or large uterine fibroids.If there’s a discrepancy of more than 3 centimeters between the expected fundal height and weeks of gestational age, this is typically referred to as “size less than dates” and may indicate the fetus is growth restricted.
In this case, your next step is to perform a growth ultrasound to evaluate the estimated fetal weight, or EFW, and amniotic fluid volume.
Here’s a clinical pearl! For pregnancies with identifiable risk factors for FGR, a growth ultrasound is routinely recommended as early as 28 weeks, regardless of the fundal height measurement.
Next, check the criteria used to date the pregnancy to ensure that the estimated due date, or EDD, utilized for the calculation of EFW is appropriate.
The most reliable method for determining the EDD is a first-trimester ultrasonographic crown-rump length. Alternatively, a pregnancy is considered to be suboptimally dated if no ultrasound examination, confirming or revising the EDD, is performed prior to 22 weeks of gestation.
Okay, once you have confirmed the dating, review the results of your growth ultrasound. The EFW is determined by measuring four main parameters: the biparietal diameter, head circumference, abdominal circumference, or AC, and femur length.If the EFW or the AC is less than the 10th percentile for gestational age, you can diagnose FGR.
Once confirmed, perform a detailed obstetrical ultrasound including fetal anatomy, if not previously completed, and look for any fetal anomalies.
Also, assess and document the gestational age at which FGR is diagnosed.Now, if your patient is diagnosed with FGR before 32 weeks of gestation, it is typically referred to as early onset FGR.

Early onset FGR (<32 wks)4:30–5:51

Early onset FGR is usually attributable to fetal causes including genetic, structural, or infectious causes. As such, all patients with early onset FGR require referral for genetic counseling and should be offered fetal diagnostic testing, including chromosomal microarray analysis, or CMA.This is performed via chorionic villus sampling or amniocentesis, with amniocentesis being the test of choice after 15 weeks of gestation.
Additionally, be sure to review the findings of the detailed ultrasound to identify any structural causes for FGR, such as congenital heart disease, diaphragmatic hernia, abdominal wall defects, or neural tube defects.
Finally, consider infectious causes of FGR, such as cytomegalovirus, toxoplasmosis, rubella, or varicella zoster.Here’s a clinical pearl: More than half of fetuses with trisomy 13 or 18 will also have FGR.
Okay, let’s talk about patients diagnosed with FGR at or after 32 weeks of gestation. This is referred to as late-onset FGR.

Late onset FGR (≥ 32 wks) 5:51–7:23

In these cases, suspect a maternal or placental cause of FGR rather than a fetal cause. Maternal causes include medical and obstetric conditions that reduce the uteroplacental blood flow and oxygen delivery to the fetus.
Conditions such as chronic hypertension, chronic kidney disease, pregestational diabetes, lupus, APS, and chronic pulmonary or cardiac disease may all contribute to FGR.
Additionally, suboptimal fetal growth is associated with substance use disorder and teratogenic medication exposure. Placental causes to consider may be gross abnormalities such as a single umbilical artery, velamentous or marginal cord insertion, chronic placental abruption, or bilobed placenta.
For these patients, begin by counseling them on any modifiable lifestyle interventions that may improve fetal growth, such as cessation of substance use or teratogenic medications, as needed.
Review the findings of the ultrasound to assess for placental causes. Finally, consider fetal diagnostic testing with CMA if there is a concurrent structural malformation, polyhydramnios, or both on ultrasound imaging.
Okay, let’s discuss management! Once FGR is diagnosed, initiate increased antenatal surveillance, including nonstress tests, biophysical profiles, and serial growth ultrasounds.

Management 7:23–10:16

In addition, monitor placental function by umbilical artery Doppler velocimetry, or UA Doppler, which measures the impedance, or resistance, to blood flow along the fetal component of the placenta.
Because of the normally low impedance of fetal circulation, there should be continuous forward flow in the umbilical artery throughout the cardiac cycle.
Conversely, if placental insufficiency is present, UA Doppler will show absent or reverse end-diastolic flow.Now, the frequency of antenatal surveillance is determined both by the severity of FGR as well as the degree to which the Dopplers are abnormal.
Management of pregnancies with an estimated fetal weight between the 3rd and 10th percentile with normal UA Dopplers includes weekly antenatal surveillance to track fetal growth along with UA Dopplers performed every 1 to 2 weeks with delivery recommended between 38 and 39 weeks.
However, if the Dopplers show a decreased end-diastolic flow or severe FGR is noted, defined as an EFW less than the 3rd percentile for gestational age, weekly Dopplers are recommended; and delivery is typically performed at 37 weeks and 0 days of gestation.
Pregnancies with UA Dopplers showing absent or reversed diastolic flow generally require more intensive antenatal surveillance as well as even earlier delivery timing.
In cases of absent diastolic flow. Dopplers are recommended 2 to 3 times weekly and delivery is performed at 33 to 34 weeks and 0 days of gestation.
In cases of reversed end diastolic flow, counsel your patient on hospitalization for monitoring, corticosteroids for fetal lung maturity as indicated, nonstress tests for fetal monitoring 1 to 2 times daily, and delivery between 30 and 32 weeks and 0 days of gestation.Here’s a final clinical pearl!
Early onset FGR typically is more severe as opposed to late onset FGR and more often shows a pattern of umbilical artery deterioration.
It also tends to be symmetrical, meaning that the weight, length, and head circumference are all less than the 10th percentile.
This is in contrast to late onset FGR, which tends to be asymmetrical with a low weight but normal length and head circumference.
UA Dopplers are also typically normal with late onset FGR.Alright, as a quick recap… Fetal growth restriction is defined as an estimated fetal weight or abdominal circumference below the 10th percentile for gestational age, as determined by ultrasound measurements.

Review 10:16–10:56

When fetal growth restriction is suggested by either patient history or a physical exam with a lagging fundal height for dates, a growth ultrasound can confirm the diagnosis.
Patients with fetal growth restriction require increased antepartum surveillance with serial growth ultrasounds and umbilical artery Doppler.
The severity of fetal growth restriction and UA Doppler determines the frequency of antepartum surveillance and delivery timing.