Fetal Growth Restriction (FGR), also known as Intrauterine Growth Restriction (IUGR), refers to a condition where a fetus is unable to grow at the expected rate within the womb. This condition is associated with an increased risk of complications during pregnancy, labor, and postnatal development. FGR is a critical aspect of prenatal care because it can impact both the immediate health of the baby and its long-term growth and development.
What is Fetal Growth Restriction (FGR)?
Fetal growth restriction occurs when a fetus fails to reach its genetically determined growth potential. This condition is usually identified when the fetal weight is below the 10th percentile for its gestational age, meaning it is smaller than at least 90% of other fetuses at the same stage of pregnancy. FGR is typically diagnosed through ultrasound measurements that estimate fetal weight and assess the growth patterns.
FGR can be classified into two main categories:
- Symmetric (early-onset) FGR: The fetus is proportionally small, with both head and body measurements smaller than expected. This type of FGR often results from factors affecting fetal development during the first trimester.
- Asymmetric (late-onset) FGR: The fetus’s head size remains normal, but the body (particularly abdominal size) is smaller than expected. This type is more common in the third trimester and is typically related to placental insufficiency.
Causes of Fetal Growth Restriction
FGR can result from a variety of factors, either related to the mother, the placenta, or the fetus. Understanding the underlying causes of FGR is important for determining appropriate management and treatment.
Maternal Factors
- Hypertension: Conditions such as chronic hypertension or preeclampsia can impair blood flow to the placenta, reducing oxygen and nutrient supply to the fetus, leading to growth restriction.
- Infections: Certain infections like cytomegalovirus (CMV), toxoplasmosis, rubella, and syphilis can affect fetal growth.
- Chronic health conditions: Diabetes, autoimmune diseases (e.g., lupus), and kidney disease can increase the risk of FGR.
- Nutritional deficiencies: A poor diet, particularly one deficient in essential nutrients like folic acid, iron, or protein, can hinder fetal development.
- Smoking and substance abuse: Smoking, alcohol, and drug use during pregnancy significantly increase the risk of FGR. Nicotine, for example, constricts blood vessels and reduces blood flow to the placenta.
- Poor weight gain: Inadequate maternal weight gain during pregnancy, especially in the second and third trimesters, can contribute to poor fetal growth.
- Age: Extremes in maternal age (either teenagers or women over 35) can be associated with an increased risk of FGR.
- Placental disorders: Abnormalities such as placental insufficiency, placenta previa, or placental abruption can reduce the ability of the placenta to supply adequate nutrients and oxygen to the fetus.
Placental Factors
- Placental insufficiency: One of the most common causes of FGR, it occurs when the placenta does not develop properly or becomes damaged. This reduces its ability to provide adequate blood, oxygen, and nutrients to the fetus, leading to growth restriction.
- Placenta previa: A condition where the placenta covers or is located very close to the cervix, which can lead to poor fetal growth.
- Placental abruption: When the placenta detaches prematurely from the uterine wall, it can cause bleeding and disrupt the nutrient supply to the fetus.
Fetal Factors
- Chromosomal abnormalities: Certain genetic conditions, such as Down syndrome or Turner syndrome, can lead to fetal growth restriction.
- Congenital infections: Infections that the fetus acquires while in the uterus, such as syphilis, rubella, or CMV, can affect fetal growth.
- Multiple gestations: Twins, triplets, or other multiples have a higher risk of developing FGR due to competition for nutrients and space in the uterus.
- Fetal abnormalities: Structural or developmental abnormalities in the fetus, such as heart defects or problems with the gastrointestinal or renal systems, can interfere with growth.
Symptoms and Diagnosis of FGR
FGR may not have obvious symptoms in the early stages. However, it can be detected through routine prenatal care, especially during the second trimester. Common methods of diagnosing FGR include:
Ultrasound Imaging
- Fetal biometry: Ultrasound measurements of the fetal head, abdomen, and femur length can assess whether the fetus is growing at a normal rate. If measurements are below the 10th percentile for gestational age, FGR may be suspected.
- Doppler ultrasound: This test uses sound waves to measure blood flow in the umbilical artery and other vessels in the placenta. Reduced blood flow can be an indication of placental insufficiency, which is a common cause of FGR.
Clinical Signs
- Decreased fetal movement: Mothers may notice fewer fetal movements if the fetus is not growing adequately. This is a key sign of possible FGR and should be investigated by healthcare providers.
- Fundal height measurement: A smaller-than-expected fundal height (the distance from the pubic bone to the top of the uterus) may indicate restricted fetal growth, though this measurement alone is not always sufficient to diagnose FGR.
Maternal Health History and Screening
- Blood pressure monitoring: High blood pressure or a history of hypertension increases the risk of FGR.
- Urine tests: To check for proteinuria, which may indicate preeclampsia or other complications that could affect fetal growth.
- Lab tests: Blood tests may be done to rule out infections or nutritional deficiencies that could be contributing to FGR.
Complications of FGR
FGR is associated with an increased risk of both maternal and fetal complications:
Maternal Complications
- Preeclampsia: The condition is more common in women who are carrying a growth-restricted fetus.
- Preterm labor: Women with FGR may need early delivery to prevent complications such as stillbirth or fetal distress.
- Placental abruption: The risk of placental detachment is higher in women with FGR.
- Postpartum hemorrhage: Due to placental problems, women with FGR may experience excessive bleeding after delivery.
Fetal Complications
- Preterm birth: FGR fetuses are more likely to be born prematurely, which increases the risk of complications such as respiratory distress syndrome, jaundice, and feeding difficulties.
- Low birth weight: FGR infants are more likely to be born with a birth weight under 5 pounds, 8 ounces (2,500 grams), which puts them at greater risk for neonatal complications.
- Hypoxia and asphyxia: Limited oxygen supply to the fetus due to placental insufficiency can lead to brain injury or other complications.
- Long-term health problems: FGR infants may be at higher risk for metabolic disorders like diabetes, obesity, and cardiovascular diseases later in life.
Management and Treatment of FGR
The management of FGR depends on the severity of the condition and how far along the pregnancy is. Key strategies for managing FGR include:
Close Monitoring
- Frequent ultrasounds: To track fetal growth, amniotic fluid levels, and blood flow in the umbilical cord and placenta.
- Non-stress tests (NST): To assess fetal heart rate patterns and check for signs of fetal distress.
- Biophysical profile (BPP): A comprehensive test that combines ultrasound and NST to evaluate fetal wellbeing.
Early Delivery
In cases of severe FGR or when the fetus shows signs of distress, early delivery may be necessary, even if the pregnancy is preterm. If the fetus is well-formed and there are signs that the placenta is no longer functioning properly, inducing labor or performing a caesarean section may be the best option to prevent further complications.
Managing Maternal Conditions
- Controlling hypertension: Blood pressure medications may be prescribed to manage maternal hypertension or preeclampsia.
- Diet and nutrition: Ensuring that the mother receives adequate nutrition to support both her health and the growth of the fetus.
- Steroid administration: If premature birth is imminent, corticosteroids may be given to help mature the baby’s lungs.
Interventions for Placental Insufficiency
If placental insufficiency is the cause of FGR, treatments may involve increasing the maternal blood flow to the placenta, but the most definitive treatment is often delivery of the baby.
Prevention of FGR
While not all cases of FGR can be prevented, some measures can reduce the risk:
- Prenatal care: Regular prenatal visits help detect potential problems early.
- Healthy lifestyle: Maintaining a balanced diet, refraining from smoking and alcohol, and managing chronic conditions like hypertension and diabetes before and during pregnancy can reduce the risk of FGR.
- Blood pressure management: Managing maternal blood pressure effectively can help reduce the risk of placental insufficiency and FGR.
Conclusion
Fetal growth restriction is a serious pregnancy complication with significant risks for both mother and baby. Early diagnosis and intervention can improve outcomes, particularly through monitoring fetal health, managing maternal conditions, and deciding on early delivery when necessary. With appropriate prenatal care and timely interventions, many babies with FGR can survive and thrive, although some may experience long-term health challenges.