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
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.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.