Intrauterine growth restriction, also known as fetal growth restriction, is a term used to describe poor growth of a fetus inside the mother’s womb. Intrauterine growth restriction is most commonly associated with poor nutrition or inadequate oxygen supply to a fetus. It can have potentially life-threatening effects on the fetus. Intrauterine growth restriction (IUGR) is a major focus when assessing the health and progression of a pregnancy.
Types of Intrauterine Growth Restriction
Symmetrical or primary IUGR occurs when all fetal organs are reduced in size. This condition is less common than asymmetrical intrauterine growth restriction. It accounts for roughly 20% to 25% of all intrauterine growth restriction cases. However, it is more likely to lead to long-term physical or neurological conditions. Symmetrical intrauterine growth restriction typically occurs earlier in the pregnancy.
Asymmetrical, or secondary intrauterine growth restriction is a more common form. In this scenario, the fetal head continues to grow at a normal or near-normal rate while the body is stunted in growth. As a result, fetal development and well-being is not as compromised as with symmetrical intrauterine growth restriction. Asymmetrical intrauterine growth restriction typically becomes evident during the third trimester.
Risk Factors and Causes
Intrauterine growth restriction is believed to be primarily influenced by extrinsic, or non-essential factors affecting the fetus. These factors are commonly associated with the physical condition of the mother during pregnancy. Other causes of intrauterine growth restriction include intrinsic factors, such asgenetic and pathological abnormalities.
Risk factors for intrauterine growth restriction may involve:
- Maternal weight under 100 pounds
- Poor nutrition during the pregnancy
- Use of cigarettes, drugs, or alcohol
- Pulmonary, cardiovascular, or renal disease
- Pre-gestational or gestational diabetes in the mother
- Low levels of amniotic fluid
- Chromosomal abnormalities or birth defects
- Umbilical cord damage or abnormalities
- Placental damage or abnormalities
Diagnosis and Treatment
Screening is important for early diagnosis of intrauterine growth restriction. However, there is no single test or measurement tool to accurately determine the condition. The mother should undergo periodic monitoring by a medical professional to ensure satisfactory fetal growth rates and amniotic fluid levels. If intrauterine growth restriction is indicated, early delivery may be recommended.
One measurement taken is fundal height, or the size of the uterus from the uterine top to the top of the mother’s public bone. Fundal height is compared with gestational age to determine proper growth and development. Ultrasound and Doppler ultrasound can also be used to create a visual image of the fetus. The medical professional can compare the results of these screening methods to estimate growth rates.
Intrauterine growth restriction can be potentially fatal for the fetus if left undiagnosed or untreated. It can also contribute to the development of several related conditions that compromise fetal survival rates. It is estimated that 4 million neonatal deaths occur worldwide every year. Of these 4 million, 60% are associated with low birth weight caused by intrauterine growth restriction, preterm delivery, and genetic abnormalities.
Intrauterine growth restriction may increase fetal risk of:
- Need for cesarean delivery
- Meconium ingestion or aspiration
- Cerebral palsy
- Pulmonary hemorrhage
- Hypoxia, or lack of oxygen
- Hypoglycemia, or low blood sugar
- Hypocalcaemia, or decreased blood calcium levels
- Polycythemia, or increased red blood cell count
- Leukopenia, or decreased white blood cell count
- Thrombocytopenia, or decreased blood platelet count
- Hyperviscosity, or decreased blood flow to increased red cell numbers