What is intrauterine growth restriction (IUGR)?
Intrauterine Growth Restriction (IUGR) is a condition that occurs when a developing fetus is smaller in size than what is expected for its gestational age. In cases of IUGR, the estimated fetal weight typically falls below the 10th percentile, meaning it’s smaller than 90% of other fetuses at the same stage of pregnancy.
Intrauterine Growth Restriction can manifest at any point during pregnancy. Early-onset IUGR is frequently associated with factors such as chromosomal abnormalities, maternal health conditions, or significant issues with the placenta. Late-onset growth restriction, typically occurring after the 32nd week of pregnancy, tends to be linked to different underlying problems.
With IUGR, the baby’s overall growth, including the development of organs and tissues, is constrained. This results in organ and tissue cells that may not grow to their expected size or number. In cases where there is inadequate blood flow through the placenta, the fetus may receive insufficient oxygen, leading to a decrease in the fetal heart rate and posing significant risks to the baby.
Types of Intrauterine Growth Restriction
- Symmetric (or primary) IUGR: In this type, all of the fetal body parts are smaller in size than expected. Symmetric IUGR accounts for approximately 30% of all IUGR cases.
- Asymmetric (or secondary) IUGR: Here, only the fetus’s abdomen is smaller than expected, while the head and brain are of the typical size. Asymmetric IUGR is more common, making up 80% of all IUGR cases.
How common is fetal growth restriction?
Fetal growth restriction, or intrauterine growth restriction, impacts approximately 10% of all pregnancies. It’s worth noting that a fetus can be smaller than the average size without having IUGR.
What causes intrauterine growth restriction?
Intrauterine growth restriction (IUGR) occurs when an issue or anomaly hinders the growth of cells and tissues, potentially leading to a decrease in cell size. This can be a result of inadequate nutrient and oxygen supply to the fetus, which are essential for the growth and development of organs and tissues. Infections can also be a contributing factor. Some elements that might play a role in IUGR include the following:
- Maternal-related factors: These involve chronic diseases affecting the mother’s heart, lungs, kidneys, liver, or blood (such as severe high blood pressure, diabetes, or autoimmune disorders), as well as behaviours like smoking or substance abuse. Additionally, exposure to certain medications (like specific anticonvulsants) and infections that can be transmitted to the baby (such as cytomegalovirus or rubella) can play a role.
- Baby-related factors: This group includes birth defects, chromosome or genetic abnormalities, infections in the developing fetus, and being part of a multiple birth, such as twins or triplets.
- Placenta and uterine-related factors: These encompass issues like having a small placenta, abnormal blood flow through the placenta, the presence of large uterine fibroids behind the placenta, the existence of placental masses (which are benign tumours made up of abnormally grouped blood vessels), abnormal insertion of the umbilical cord into the placenta, placental abruption (where an area of the placenta separates from the uterus), and having an abnormally shaped uterus.
When is Intrauterine Growth Restriction (IUGR) detected?
During pregnancy, there are various methods to estimate the size of the developing fetus. One approach involves measuring the height of the fundus, which is the upper part of the mother’s uterus, starting from the pubic bone. This measurement, typically expressed in centimetres, typically aligns with the number of weeks of pregnancy after the 20th week. If the fundus measurement is lower than expected for the specific week of pregnancy, it may suggest that the baby’s size is smaller than anticipated. Additionally, there are other diagnostic procedures that can be used to assess fetal growth.
- Ultrasound: Ultrasound, which utilizes sound waves to generate images of internal structures, offers a more precise means of estimating fetal size. This involves measuring the head and abdomen of the fetus and then comparing these measurements with a growth chart to gauge fetal weight. Specifically, the fetal abdominal circumference is a valuable indicator for assessing fetal nutrition.
- Doppler flow: Doppler flow is an alternative method for assessing and diagnosing intrauterine growth restriction (IUGR) in pregnancy. This technique uses sound waves to evaluate blood flow. The motion of blood within blood vessels generates waveforms that provide information about the speed and volume of blood moving through those vessels. Doppler flow studies can be used to examine the blood flow in the fetal brain and the umbilical cord, offering valuable insights into the condition.
- Mother’s weight gain: The weight gain of the mother during pregnancy can serve as an indicator of the baby’s size. A mother’s limited weight gain during pregnancy might be associated with the birth of a smaller baby.
How is IUGR treated?
The treatment for intrauterine growth restriction (IUGR) depends on the gestational stage and the baby’s condition. Medical professionals will closely monitor the baby’s development during prenatal check-ups, utilizing ultrasounds to track growth and identify any potential issues.
If the mother has an underlying medical condition, doctors will assist in its management. This may involve ensuring she follows a balanced and nutritious diet and maintains appropriate weight gain during pregnancy. In some cases, bed rest may be recommended to enhance blood flow to the baby.
In certain situations, doctors may advise inducing labour and delivery prematurely. This action could be taken if the baby’s growth has significantly slowed, or if there are complications involving the placenta or umbilical cord blood flow. In cases where the stress of a vaginal delivery poses a significant risk to the baby, a cesarean section (C-section) may be recommended.