IUGR can result in the birth of a baby who is considered small-for-gestational-age (SGA). Fetal growth is determined by measuring the fundal height – that is, from the top of the public bone to the top of the uterus. This measurement in centimeters approximately equals the number of weeks gestation. If your clinician finds this measurement is smaller than expected, an ultrasound exam may be recommended to more closely determine the fetus’ growth. During the ultrasound examination, measurements are taken of various fetal body parts to determine the approximate weight of the fetus. This weight is compared with the average weight for fetuses at the same gestational age. The average percentile is 50 but anything between the 10th and 90th percentile is considered with the normal range. In other words, 10 percent of the population are smaller than normal and 10 percent are larger than normal. This is not to say that all fetuses above and below 10 percent are not normal – most are completely normal. It does indicate to your clinician that some may not be thriving and may need to be followed more closely.

The fetus whose estimated weight falls under or below the 10th percentile may have intrauterine growth restriction. The following are some of the possible causes of IUGR:

• There may be multiple fetuses.
• Some genetic factors may result in less than average fetal growth.
• Certain infections such as cytomegalovirus, measles and toxoplasmosis may affect growth.
• Chromosomal abnormalities are known to affect growth.
• Poor nutrition in the mother particularly in the third trimester.
• Smoking is known to decrease birth weight.
• Alcohol, cocaine use and other environmental toxins are also known to decrease birth weight.

The fetus estimated to be above the 90th percentile may have macrosomia, that is, being large-for-gestational-age (LGA). The possible causes of a LGA baby may be:

• The mother is a poorly controlled diabetic.
• The pregnancy goes beyond 40 week gestation.