(For information specific to the case of twins, visit SIUGR information page)
Intrauterine growth restriction (IUGR) is used interchangeably with the terms fetal growth restriction and small for gestational age, and identifies a fetus that is small and potentially at risk for complications.
The diagnosis of IUGR is made by ultrasound and is defined as an estimated fetal weight (EFW) of <10th percentile for any given gestational age during the pregnancy (normal EFW is 10th to 90th percentile).
What causes it?
It is most important to note that the majority of fetuses (70%) diagnosed with IUGR are actually normal, but just small in nature.It is really those fetuses that are <3rd percentile that are more likely to be abnormally small and truly at risk. The list of causes for IUGR is quite long, but the vast majority will be due to one of the following:
- Poorly established due date
- Constitutionally small fetuses (e.g. parents are of short stature)
- Chronic medical conditions in the mother (e.g. hypertension)
- A primary placental or umbilical cord problem
- Risky social habits (tobacco, alcohol, drugs)
Less common, but significant and serious causes include chromosomal abnormalities, genetic syndromes and intrauterine infections (e.g. cytomegalovirus).
Risks to the fetus and mother?
The fetus that is IUGR is at risk for stillbirth and at risk for fetal heart rate abnormalities in labor. Accordingly, the mother is at risk for cesarean delivery, which carries associated surgical risks and risks to future pregnancy. If the fetus is found to have a deteriorating status, often preterm delivery is required which carries risk for injury to different organ systems including the brain, lung and bowel. Further, fetuses that are growth restricted are at risk for long-term complications including cerebral palsy and even chronic medical conditions like hypertension and diabetes as an adult.
There are limited treatment options for IUGR, but they are dependent on the underlying cause. If a mother has poorly controlled diabetes or poorly controlled hypertension (or other chronic medical condition), these can be addressed by her obstetrical provider. Cessation of substance abuse has been shown to be beneficial, and reduce the progression of the condition. The optimal time to control medical conditions and to discontinue substance abuse is prior to pregnancy because once the placenta has developed fully, there is little that can be done to truly improve placental function, but continuation of a poorly controlled condition or substance use can cause progression. If there is a primary placental maldevelopment issue, little can be done except for surveillance. Hydration is encouraged as a well-hydrated mother can insure that the maternal circulation through the uterus at least carries good fluid volume. Strict bedrest is discouraged as it has never been shown to reduce preterm birth or hypertensive disorders in pregnancy, and does not improve fetal growth. However, bedrest does increase the risk for blood clot formation in the mother which can be life-threatening. There are no treatments that can change a genetic cause for an IUGR fetus. There are limited treatments for infections that cause IUGR. Sometimes delivery of the fetus is the treatment as it removes the fetus from the environment that may have caused the IUGR and potentially can be life saving (e.g. avoiding stillbirth).
Surveillance and Delivery
Pregnancy surveillance of the IUGR fetus is performed by ultrasound assessing fetal growth ultrasounds, amniotic fluid, and blood flows in the fetus and placenta. In the third trimester, generally after 30 weeks of pregnancy, additional surveillance of the fetal status is performed weekly or twice-weekly. This additional surveillance includes either non-stress testing (fetal heart rate monitoring with a device placed on the mothers abdomen) and amniotic fluid assessment or a biophysical profile (performed with ultrasound assessing fetal movement, breathing, tone and amniotic fluid). The timing of delivery is extremely variable depending on the underlying cause and the status of the baby in the womb, but most deliveries occur in the early term to term period.