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When Baby’s Too Small: Intrauterine Growth Retardation
If you’re pregnant, you may have wondered why your doctor measures your uterus at each prenatal visit. The answer is just what you might expect: the measurement helps your health care provider estimate how well your baby is growing. Some babies grow significantly more slowly than expected, and may have intrauterine growth retardation, or IUGR. This term refers to delays in physical growth, rather than cognitive development, and is associated with a higher risk of problems before and during delivery.

If your exam suggests your developing baby is too small, your health provider is likely to review your records to be certain of your baby’s gestational age. Checking the date of your last menstrual period, the timing of your first positive pregnancy test and reviewing information from your earliest ultrasound may lead your provider to recalculate your baby’s gestational age. Sometimes a revised calculation reveals a younger gestational age than initially thought, providing a reassuring explanation for the small measurement.

Some babies are small for the simple reason that their parents are small. If a mother is under 5 feet tall, for example, there’s good reason to suspect her baby will be small as well. There are also regional variations: pregnancies at higher altitudes tend to produce babies with lower birth weights.

When IUGR is suspected, additional testing is useful. An ultrasound provides a visual picture of your baby and allows your doctor to obtain measurements, see the amount of amniotic fluid and evaluate the development of the placenta.

There are two main categories of IUGR: asymmetric and symmetric. In asymmetric IUGR, a baby shows normal head and long bone growth, but has a smaller than expected abdominal size. Symmetric IUGR refers to a baby who has equally smaller than expected head, abdomen and long bones.

There are multiple causes of IUGR. It may reflect a decline in the ability of the placenta to nourish a growing baby, such as when high blood pressure reduces placental blood flow to the placenta.

Common causes of IUGR include the following:
  • Twinning—twins have a 15 to 25 percent chance of IUGR

  • Cigarette use during pregnancy

  • Alcohol use during pregnancy

  • Maternal malnutrition

  • High blood pressure during pregnancy

  • Maternal medical conditions such as Lupus, kidney or inflammatory bowel disease

  • Prenatal infections such as syphilis, cytomegalovirus, toxoplasmosis or rubella

  • Chromosomal anomalies of the fetus including trisomy 21 and trisomy 18
If IUGR is diagnosed, your doctor will review your medical history to learn about your use of medications, recent infections, occupational exposures and possible substance abuses. Your doctor may request ultrasound exams to estimate the quantity of amniotic fluid around your baby, the pattern of blood flow within the umbilical cord and the stage of placental maturation. Blood tests may also be performed to check for infections.

To closely monitor your baby’s well being, additional tests may be requested. Some common tests are the biophysical profile (BPP), the non-stress test (NST) and the contraction stress test (CST). All of these tests include fetal heart rate monitoring to evaluate for signs of fetal stress. If your baby appears to be doing well with these assessments, another ultrasound may be performed in three to four weeks to follow your baby’s growth. If testing reveals additional concerns, an induction of labor may be advised prior to the due date. Typically, an effort is made to balance the risk of inducing labor early with the risk to the baby of continuing a pregnancy with insufficient placental blood flow.

The good news is that most babies born with IUGR are able to catch up on growth following delivery. These babies are able to obtain better nutrition and grow more appropriately after they enter the world.

Laura E. Stachel M.D. Obstetrician & Gynecologist