Intrauterine growth restriction (IUGR) is a condition in which a baby does not grow normally within the womb, and the rate of growth is below the 10th percentile for that particular period of pregnancy. IUGR is often due to a complex mix of several factors.
Most babies with IUGR are born in developing or underdeveloped regions of the world, especially in Asian countries.
Causes
The main causes of IUGR could be classified under the following headings:
- Related to the genes of the parents or baby
- Related to the baby alone
- Related to the mother alone
- Related to the placenta
IUGR commonly results from a combination of these:
Maternal Causes
Mothers with too-small babies are often:
- Below the age of 16 or above the age of 35 years
- Living in the hills
- Poor, uneducated, or from one of the underdeveloped regions of the world
- Smokers, drinkers, or drug users
- On medications such as warfarin, chemotherapy, or steroids, or any drug which interferes with normal cell growth
- Forced to work too hard at too heavy jobs
- Having babies born too close together (less than 6 months apart) or too far apart (more than 10 years apart)
- Small and undernourished, with a body mass index below 20 or a body weight below 45 or above 75 years
- Having their first baby or their sixth (or higher order) baby
- Having a baby as a result of treatment with assisted reproduction technologies (ART)
- Already mothers of a too-small baby
- Have medical conditions such as bronchial asthma, heart defects, autoimmune disorders, blood disorders, hypertension or kidney disease, diabetes, or infections including STIs – these conditions may precede the pregnancy or be brought on by it, or become worse during the pregnancy
- Not gaining weight properly during pregnancy
- Not able to get medical care during pregnancy
Fetal
Sometimes the baby’s health condition is responsible for the failure to grow properly. This can include:
- Abnormal genes or chromosomes such as:
- Trisomy 13, 18 or 21
- Other abnormal chromosomal defects
- Other genetic defects
- Birth defects such as having abnormal connections between the windpipe and the food pipe (trachea-esophageal fistula), omphalocele (serious gut malformations), anencephaly (not having significant brain development) and heart defects
- Twins or higher-order pregnancies which results in the babies not getting enough food or oxygen to grow well
- Infections acquired during life in the womb, such as toxoplasmosis, malaria, syphilis, cytomegalovirus, or HIV
- Metabolic abnormalities such as failure of pancreatic development (the pancreas is responsible for digestion as well as control of blood sugar levels), galactosemia, phenylketonuria and other defects which lead to the baby being unable to use food properly to grow for lack of the right enzymes to process the nutrients
Placental
In some pregnancies, the placenta is too small or doesn’t function properly to carry enough nutrients or oxygen to the baby, as when:
- The placenta is less than 350 g in weight
- The blood vessels supplying the placenta fail to grow properly
- The mother has a condition called preeclampsia in which the placenta doesn’t function well
- Thrombophilia is present in the mother and results in a dysfunctional placenta
- Some areas of the placenta are genetically abnormal and do not function properly, so that the overall working of the placenta is not up to par
- Inflammation of the blood vessels supplying the placenta which can even lead to death of part of the placenta
- Abnormal blood vessels such as only one umbilical artery instead of two
- Placental infections
- Other placental abnormalities such as reduced activity of some crucial enzymes like thioredoxin
Further Reading