by Olaide Akande

Created on: August 17, 2009

Intrauterine growth restriction or IUGR for short is the failure of a fetus to achieve its genetic growth potential. This means that a fetus or baby is smaller than expected for its gestational age. It is diagnosed while a woman is still pregnant .if discovered after birth, the baby is usually low birth weight.

IUGR may be caused either by factors that affect the intrinsic growth potential of the baby, by maternal diseases, or problems with the placenta. Maternal under nutrition is a common cause of IUGR worldwide. Other causes include maternal smoking, drug abuse, and medical conditions such as hypertension, heart disease, diabetes and infections.

Fetal causes include conditions such as chromosomal or genetic abnormalities, congenital infections and recipient of a twin-twin transfusion syndrome. Failure of the placenta to properly attach to the mother's blood vessels (abnormal trophoblastic invasion), and preeclampsia are possible placental causes for IUGR.

To make a diagnosis of IUGR, the most important consideration must be accurate dating of a woman's pregnancy. If a woman is certain of her last menstrual period, and the period is regular, then this poses no problem. A sonogram done in the early weeks of pregnancy (between 12 and 20weeks) will also give accurate estimates of a woman's gestational age.

IUGR is suspected when the size of the uterus measured clinically using a tape, is consistently lower than the estimated gestational age (EGA) by more than three weeks. Normally the size of the uterus (in cm) should correspond to the EGA in weeks with a margin of error of 2weeks.

Other women in whom IUGR may be suspected and who will need further investigation include women with a low pre-pregnancy weight, or women who have any of the above mentioned maternal causes of IUGR.

Confirmatory diagnosis is by ultrasound measurements of specific fetal parameters. These include the head circumference, femur length, abdominal circumference and biparietal diameter (distance across a particular skull bone). When these measurements fall below the 5th percentile for expected gestation, then the fetus is classed as having IUGR.

Serial measurements are more precise in diagnosing IUGR than one specific measurement. This will help show indeed whether a fetus's growth is restricted as opposed to it being only constitutionally small. A detailed scan of the fetal anatomy will also help determine if the cause is from a congenital abnormality

Fetuses with normal head circumference but reduced abdominal circumference are more likely to be suffering from IUGR as a result of uteroplacental insufficiency. Symmetrically small fetuses i.e. fetuses in whom their biometry are equally small usually result from the other causes of IUGR.

Measuring the amount of amniotic fluid(the fluid which surrounds the fetus) may also help in diagnosing IUGR. This is also done using ultrasonography. A reduced level of amniotic fluid (oligohydramnios) is a common feature of fetuses that have IUGR.

IUGR is diagnosed with the aid of the ultrasound machine by measuring fetal biometry, detailing fetal anatomy, and checking the amount of amniotic fluid. The key precedent however, is accurate estimation of a woman's gestational age. Without doing this, fetuses that are normal may be wrongly classified as being IUGR and vice visa.

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