Cause of Some Growth-Retardation Mystifies Doctors : Health: An estimated 40,000 babies are born with IUGR each year in the U.S. They face complications, even death.
It is one of the most serious problems of pregnancy, a complication that affects an estimated 40,000 babies born in the United States each year. Yet despite extensive study of the problem, known as intrauterine growth retardation (IUGR), doctors have few successful treatments. In many cases, the cause of retarded growth remains a mystery.
Babies suffering from IUGR are smaller--often much smaller--than expected for their gestational age. Although many are not premature, something stunts their growth in the womb, making them far more vulnerable to complications and death than normal-weight infants.
Some of the causes of growth retardation are well known and occur most often among poor women who receive little or no prenatal care. They include alcohol and drug use, malnutrition, smoking and inadequate weight gain during pregnancy. Less-common causes are maternal hypertension, sickle-cell disease, congenital infection or a chromosomal abnormality such as Down’s syndrome.
While virtually all growth-retarded babies are by definition low birthweight--they weigh less than 5 1/2 pounds, considerably below the median 7-pound, 7-ounce size of American newborns--not all low-birthweight babies are growth retarded. Some low-birthweight infants are genetically small, while others are premature; their low birthweight is appropriate for their gestational age.
“In the past, what used to happen is that babies who were low birthweight were automatically classified as premature even when they weren’t,” said Lawrence Grylack, associate director of neonatology at Washington’s Columbia Hospital for Women. “Now we take more care in plotting growth characteristics” and treat infants accordingly.
Despite dramatic advances in the use of ultrasonography, which have enabled doctors to determine the age, growth and health of a fetus, IUGR is often undiagnosed. In about 50% of cases, according to obstetricians who specialize in high-risk cases, it is not detected before birth.
“Even though it’s been studied fairly extensively we don’t know a lot about (IUGR),” said Jean C. Bolan, associate director of maternal-fetal medicine at Columbia Hospital. “There are a lot of cases with no apparent cause . . . . What we don’t have is a good treatment or foolproof diagnostic criteria.”
If doctors know in advance that a woman is at risk, particularly if she has given birth previously to a growth-retarded baby, they are much more likely to monitor a pregnancy carefully. But among women who don’t appear to be high risk, IUGR may be overlooked until it is too late.
“Some cases are just flat-out missed,” said John H. Grossman, director of maternal-fetal medicine at George Washington University Medical Center. “They happen to women who do everything right, who go for prenatal care religiously and see good doctors, and it just isn’t picked up.”
In making a diagnosis of IUGR, doctors consider a variety of factors. They include a baby’s length, its head circumference--an important indicator of fetal brain development--as well as its race and nationality.
Growth-retarded babies are not usually mentally retarded, unless their size reflects an underlying chromosomal abnormality or serious infection, which typically affects the fetus early in pregnancy.
Because IUGR has so many causes, the long-term prognosis for affected infants varies tremendously. “The studies are very mixed and show everything from these kids being perfectly normal to a horrendous amount of learning disabilities, school failure, hyperactivity and mental retardation,” said Robert L. Goldenberg, professor of obstetrics and gynecology at the University of Alabama at Birmingham and a leading IUGR researcher. “The thing to keep in mind is that this is such a heterogenous group.”
How well growth-retarded babies do, Goldenberg and others say, depends on a variety of factors: the cause and severity of growth retardation, complications during or immediately after birth, catch-up growth during the first six months of life and the infant’s home environment. The most critical factor is whether the baby’s brain has been spared. In about 60% of cases, the head is of normal size, indicating that the fetus has essentially burned its meager reserves of fat in order to protect its brain.
Despite the potential for complications, doctors say that babies with brain-sparing IUGR tend to fare better than premature infants, many of whom have respiratory problems. “Growth-retarded babies do much better outside the uterus than premature babies of the same weight,” said Grossman. “It may be that putting these babies under some stress accelerates (lung) maturation.”
Even the science, doctors say, is imperfect. Although suspected IUGR can be detected by a sonogram, “it’s not so easy to recognize all the time,” said Maureen C. Edwards, chief of Newborn Services at GW.
In some cases, measurement of a fetus’s abdominal or head circumference--markers of retarded growth--can be hampered by its position in the womb. Furthermore, according to Jose Lopez-Zeno, assistant professor of maternal-fetal medicine at GW, sonograms have a 10% to 15% margin of error in calculating fetal weight.
Retarded growth detected early in pregnancy usually indicates a more serious problem, such as Down’s syndrome. Cases that occur later, after the 32nd week, when pregnancy-induced hypertension often develops, typically have a better prognosis because the fetus is more fully developed.
When IUGR is detected late in pregnancy, there is little doctors can do other than watch and wait. Some physicians recommend that women be hospitalized and placed on total bed rest in an effort to increase blood flow to the placenta, which provides nourishment and oxygen to the fetus.
“It’s a question of making the assessment of whether the baby is better in or out,” said Bolan. Because growth-retarded babies are often too fragile to withstand the stress of labor, delivery by Cesarean section is common.
Although there are few treatments for IUGR, there may be ways to help prevent it. Several studies by Goldenberg and others have shown that women who are short and thin, particularly those who weigh less than 105 pounds when they conceive, are at significantly higher risk for delivering a growth-retarded baby.
That is one reason the Institute of Medicine two years ago recommended that normal-sized and thin women gain more weight than doctors previously considered advisable.
“It’s a new concept that not all doctors are aware of or believe in,” said Lopez-Zeno, who recommends it for his patients.
