a closer look at iugr tiny but mighty:

byerin zinkhan, md

Even though intrauterine growth restriction (IUGR) is relatively common, most parents have never heard of it until their pregnancy is complicated by it. In IUGR, a baby does not grow as much as he or she was supposed to before birth. Currently, there is no weight cutoff to define whether a baby has growth restriction, which can make it difficult for doctors to diagnose, except in the more severe cases.

BBecause of the difficulty in diagnosing growth restriction, we do not know exactly how many babies are impacted by it. We estimate that growth restriction affects 3-14% of pregnancies in developed countries, or between 100,000 and 400,000 pregnancies per year in the United States. Known Causes There are many causes of growth restriction. Doctors think that most common causes of growth restriction are due to the same underlying issue, which is that the fetus does not get enough nutrition and oxygen in the womb. In developed countries, the most common cause of growth restriction is preeclampsia. Preeclampsia is a condition unique to pregnant women. A pregnant woman with preeclampsia often has high blood pressure, headaches, abdominal pain, and protein in her urine. Other common causes of growth restriction are the use of substances such as tobacco, abnormal development of the placenta, and chronic health conditions in the mother, such as high blood pressure, kidney disease, and lung disease. Twins and other multiples have a unique risk for growth restriction. Sharing a womb can cause crowding, which can limit growth. When twins share a placenta, sometimes unequal blood flow can develop. This unequal blood flow can lead to one fetus getting less nutrition than the other and one twin becoming growth restricted. Less common causes of growth restriction are infections and genetic conditions. Infections such as cytomegalovirus and rubella can cause growth restriction. Genetic conditions that cause growth restriction can be part of other syndromes. One syndrome that causes growth restriction is Edwards syndrome, which is also known as Trisomy 18. Uncommon problems with how the fetus develops can also cause growth restriction, such as when the fetus’s heart does not develop normally. These less common causes of growth restriction generally do not limit the nutrition and oxygen that gets to the fetus, but rather directly limit the ability of the fetus to grow. Growth restriction can affect the growth of the fetus’s whole body equally, or can affect the brain less than the rest of the body. When the brain is less affected than the rest of the body, the baby’s head size is normal to slightly small, and the baby’s length and body weight are small. This pattern is called ‘brain-sparing’ or asymmetric growth restriction. Asymmetric growth restriction often results from many of the same common causes of growth restriction, such as preeclampsia and chronic maternal health conditions. When the baby’s whole body is equally affected, the head size, length, and weight of the baby are all smaller than expected. This is called symmetric growth restriction. Symmetric growth restriction is more often caused by infections and genetic conditions.

Gauging Growth Restriction Before birth, obstetricians diagnose growth restriction when ultrasound measurements show that the fetus’s growth is slowing down or stopping altogether. Obstetricians measure the baby’s head circumference and length of the bones. They use these measurements to estimate how much the fetus weighs. Obstetricians also measure the blood flow in the umbilical cord and in the fetus to see if the fetus is doing well despite being small. Two common tests that obstetricians use to see how the fetus is doing are the non-stress test and the biophysical profile. Non-stress tests measure the fetus’s heart rate. A non-stress test result can be either reactive or nonreactive, depending on whether or not the fetus’s heart rate increases normally. A biophysical profile measures the fetus’s heart rate, breathing, movement, and amniotic fluid levels. Because growth restricted fetuses often do not get enough oxygen before birth, they are less likely to tolerate contractions from labor.

connexions 49

The biophysical profile and nonstress test results help obstetricians determine if the baby needs to be monitored more closely or if the fetus needs to be delivered, even if the fetus is not yet full term.

connexions50 Post-birth Challenges While many growth restricted babies do well after birth when they are born near their due date, they are more likely to have several health challenges. These babies are more likely to have a low blood sugar, jaundice, and thicker blood. They are also more likely to need oxygen to help them breathe and heat to help them stay warm. These tiny babies do not have much reserve to keep their blood sugar normal. While many of these babies can successfully breastfeed or bottle feed without needing help with their blood sugar, some need a special formula with extra calories, a temporary feeding tube, or intravenous (IV) sugar. Babies who have a low blood sugar are often shaky and do not eat well. Tiny babies are also more likely to have jaundice, which is caused by a buildup of bilirubin that causes a yellow color to the skin. Jaundice is common after a baby is born, and most babies do not need treatment. However, sometimes the level of jaundice is too high and needs to be treated with special lights or other therapies. Thick blood is caused by having too many red blood cells, which carry oxygen around the body. The low level of oxygen before birth makes the fetus’s body increase the number of red blood cells in order to increase the amount of oxygen in the fetus’s body. However, these extra red blood cells can cause difficulty breathing and worsening jaundice. Sometimes the thick blood needs to be treated with IV fluids and removal of the extra cells. Babies with growth restriction are more likely to have a hard time breathing and need oxygen, not just due to having thicker blood, but also due to high blood pressure in their lungs. High blood pressure in the lungs is called pulmonary hypertension and often can be treated with oxygen and other therapies. Because tiny babies do not have as much body fat, they have a harder time staying warm. Many of these babies may require extra heat and will need to stay in the newborn intensive care unit (NICU) until they can maintain their body temperature and grow without any extra heat.

Obstacles of Prematurity Growth restricted babies are more likely to be born prematurely, before 37 weeks of pregnancy. In addition to the health risks that full-term growth restricted babies face, premature babies are more at risk for health challenges unique to premature babies. The earlier that these babies are born, the greater the risk of these health challenges. These health challenges may include an infection called necrotizing enterocolitis, an eye disease called retinopathy of prematurity, and chronic lung disease of prematurity. Necrotizing enterocolitis is an infection of the bowels. Most of the time, the infection is treated with antibiotics and bowel rest. Bowel rest involves not feeding babies by mouth and using IV fluids or nutrition through an IV. Sometimes the infection is severe enough to require surgery and, in a few cases, can be life-threatening. Retinopathy of prematurity is an eye disease that can cause blindness. Advances in how doctors take care of premature babies has decreased the number of babies with retinopathy of prematurity, and the babies who

have it are less likely to need treatment for it. Treatment usually involves either laser surgery or an injection of a medication into the eyes. Usually treatment can save the baby’s eyesight. Chronic lung disease of prematurity is injury and inflammation of the baby’s lungs. It is caused by the immaturity of the lungs and the treatments that doctors conduct to help the lungs get oxygen into the body. Most babies with chronic lung disease do quite well, but sometimes these babies need oxygen for months or even may need a long-term breathing tube. Sometimes premature babies who are growth restricted are so small that doctors cannot save their lives. Life-saving measures like putting in a breathing tube and IV lines become very difficult or impossible. There is no weight cutoff under which doctors definitely will not try these life-saving measures, though often babies who weigh less than about 400 grams, or about 14 ounces, will not survive even if the initial lifesaving measures are successful. Affects into Adulthood Later in life, children who were growth restricted may have challenges with their development. This often translates to learning difficulties. However, sometimes the challenges with development can be as severe as having difficulty with eating, talking, walking, and taking care of themselves. Adults who were growth restricted as babies are more likely to have obesity, diabetes, and high blood pressure. In adults and children who were growth restricted at birth, the brain is less likely to get the normal signals that the stomach is full after eating. This change leads to eating more than needed. In these adults, the body also tends to hold on to all the calories it can get. This combination increases the risk of developing obesity. To understand why adults who were growth restricted as babies are more likely to develop these health conditions, it is important to understand how genes work. Genes are the genetic information passed down from parent to child. This genetic information does not change over time. Genes make us look different from one another. Genes are the reason that one person has brown hair and another person has blonde hair. Genes do not make changes by themselves. They need to be translated from genetic information stored in cells into information to tell our body how to function. Information from genes is translated into proteins, which are the workhorses of the body. A singular way to understand how our genes work is to think of a dimmer switch. We do not need all the lights in our house to be on fully bright all the time. We may want fully bright light in the kitchen for cooking and dimmer light in the dining room for eating. Similarly, our body decides when we need to spend energy to make more muscle after a workout or when we need to spend energy to digest food. Our body can make a little bit of one protein and a lot of another, depending on our needs at the time. Growth restriction can reprogram when genes are on and off and how much protein they make. This is like having the lights on fully bright in the dining room all the time, even when not necessary. This reprogramming of the genes is a survival mechanism to help a growth restricted fetus survive in an environment in which he or she is not getting enough nutrition during pregnancy. The genes of the growth restricted fetus are reprogrammed to hold on to all the calories that he or she gets. As mentioned before, some of these reprogrammed signals can persist throughout life and can lead to health conditions such as diabetes and obesity. Treatments + Care There are currently no specific treatments for most causes of growth restriction, but researchers are still looking. While we understand how reprogramming happens, we do not yet have any treatments to restore the reprogrammed signals to normal. In general, it is important for pregnant women to eat a healthy diet, stay hydrated, and follow up with their obstetrical providers. For children and adults who were growth restricted at birth, it is important to maintain a healthy diet and exercise. The good news is that most babies with growth restriction do well and lead full and happy lives. Being aware of the risks to the pregnant mother and baby can help parents prepare for a bright future with their tiny, but mighty baby.

Erin K. Zinkhan, MD, is a Neonatologist in Salt Lake City, Utah. She has published multiple peer-reviewed research articles about intrauterine growth restriction. Dr. Zinkhan runs the www.tinybutmightybaby.com website, a resource for parents to learn more about IUGR, and is writing a book about intrauterine growth restriction for parents (coming soon!).

connexions 51