Birth Defect Risk Factor Series: Omphalocele
Omphalocele is a birth defect where some of a baby’s organs protrude through the abdominal muscles. It occurs in about 2 out of every 10,000 births in the United States. Studies to determine the risk factors for omphalocele have had mixed results.
Figure 1. A picture of a baby with omphalocele.
Content Source: Centers for Disease Control and Prevention, National Center on Birth Defects and Developmental Disabilities
What is a birth defect?
As a baby grows inside the mother, problems sometimes happen. These problems, called birth defects, may affect how a baby looks or functions when it is born. Birth defects may be discovered during pregnancy and are usually found within the baby’s first year. Some birth defects are mild and the baby will be fine if it gets the proper treatment. Other birth defects are very severe and lead to death.
Genetics and birth defects
Some, but not all, defects occur because of a genetic problem. Genetics has to do with genes and how they are passed from parent to child. Genes are the basic unit of inheritance and determine a person’s looks, personality, intelligence and other traits. Our genes are contained in chromosomes inside the cells of our bodies. A chromosome can be thought of as a long, tightly coiled string of genes.
Chromosomes are made of long strands of DNA (Deoxy-ribo-nucleic Acid). DNA is a molecule found in our cells that provides the instructions for how we operate. It is made of 2 strands that wind around each other to form a shape called a double helix. Each gene is a specific section of the DNA molecule. (See Figure 2). Humans have around 23,000 genes in their cells.
Figure 2. The make up of a chromosome.
Courtesy: National Human Genome Research Institute
Chromosomes occur in pairs and there are 23 pairs found inside cells in the human body. A baby receives one half of each pair from its mother and one half of each pair from its father. Genetic disorders can happen when there is a mutation or change in one or more genes. Chromosomal defects such as missing pieces, extra pieces, or the wrong number of chromosomes can also result in a genetic disorder. The result may be a birth defect.
What is omphalocele?
Omphalocele (om-FA-lo-seal) is a birth defect in which a baby’s organs stick out beyond the abdominal muscles in the area of the belly button. “Omphalo” means umbilicus (also called navel or belly button) and “cele” means hernia. A hernia is when part of the body sticks out through the wall that is supposed to keep it in. Therefore Omphalocele means a hernia at the umbilicus.
The exposed organs are covered by a thin film or membrane. Sometimes this membrane may have broken and this defect may be mistaken for a similar defect called gastroschisis (ga-stros-KI-sis).
Infants with omphalocele tend to have other birth defects, including chromosomal defects (most often trisomy 13, trisomy 18, and trisomy 21). They often have a lower survival rate than infants with gastroschisis (2, 3, 6, 9, 26, 31, 38, 44, 47, 60, 62). Babies with omphalocele are often born early, have restricted growth while in the womb and have a low birth weight (35, 42, 48, 50, 57). Extremely high birth weights are not common in babies with omphalocele (66).
When does omphalocele occur?
In normal development, the intestine of the fetus should stick out or herniate into the umbilical cord by the 10th week of pregnancy. Between weeks 10 and 12, the intestine should pull back into the belly. If this does not happen, omphalocele may result.
Figure 3: Timeline showing when omphalocele occurs during pregnancy
Table 1. Estimated number of Omphalocele cases in 2005 based on number of cases for every 10,000 live births
Number of Cases for every 10,000 Live Births
Number of Live Births in 2005
Estimated Number of Omphalocele Cases
How is omphalocele diagnosed?
A Woman carrying a fetus with omphalocele has high levels of a substance called alpha-fetoprotien in her body.(11) Testing the mother for this substance along with an ultrasound of the fetus allow doctors to spot omphalocele while the baby is inside the mother. (64)
Early detection along with voluntary termination of the pregnancy has reduced the number of babies born with omphalocele in areas where voluntary termination is allowed (3, 8, 9, 15, 27, 29, 44; 47, 50, 57, 58, 59).
Why does omphalocele occur?
Risk factors are things that may cause an increased danger of a baby developing omphalocele. There is little clear evidence about what the risk factors for omphalocele are. Some possible risk factors have stronger evidence than others. Figures 3 and 4 show the number of scientific studies for and against the connection of a possible risk factor with developing omphalocele.
Demographic risk factors
Age of Mother:
Studies looking at the connection between a mother’s age and risk for a baby having omphalocele have found different results. Being an older mother seems to be linked to a higher risk of omphalocele development. The information linking being a young mother and omphalocele is not as clear.
- Five studies found that the highest risk for omphalocele occurs in the youngest and oldest mothers (8, 39, 52, 55, 60).
- Four studies found that the risk increases as the mother’s age increases (26, 28, 47, 62).
- One found a higher risk in younger but not older mothers (49).
- Three studies have reported no clear relationship between omphalocele risk and maternal age (7, 41, 57).
Older mothers may have an increased risk because of omphalocele's association with chromosomal abnormalities. These abnormalities occur more frequently with advanced maternal age. The risks associated with low birth weight and early delivery for babies with omphalocele is the same for both younger and older mothers (53).
Sex of the baby:
Most studies have found that boys have a higher risk for omphalocele than girls (3, 6, 9, 12, 28, 50, 60). There are, however, some studies that have found no differences in risk between boys and girls (26, 57, 71).
Most studies have found no relationship between race or ethnicity and omphalocele (26, 36, 52, 56, 70, 71). However, one study did find that black infants were at a higher risk of omphalocele than white infants (55).
There is no evidence that having given birth before increases the risk of having a baby with omphalocele (8, 28). However, the risk of early birth in a baby with omphalocele is higher for women who have given birth before versus women who have not (54).
Multiple Birth Pregnancy
Twins, triplets and other multiple births may have a greater risk of omphalocele compared to single babies (23, 40, 50). However one study reported no association between omphalocele and multiple baby pregnancies (32).
Other Risk Factors:
The number of babies born with omphalocele varies widely by geographic location (26, 28, 52, 60, 74). There is some evidence that babies born in rural areas are at higher risk for omphalocele than those born in cities (55).
Time of year a baby is born and being born at high altitudes are not risk factors for omphalocele (4, 14).
Babies born to parents who are related do not seem to be at higher risk of omphalocele (51).
Factors in lifestyle or environment
Babies of obese mothers are at greater risk of having omphalocele. (43, 67, 68, 69).
Babies born to mothers with hypothyroidism do not appear to have an increased risk of omphalocele (34). Hyperthyroidism is a condition of producing too much thyroid hormone which may cause weight loss,
Living close to hazardous waste sites or industrial sites has not been found to increase risk of omphalocele (13, 22). One study did find that living close to landfill sites has been associated with a slightly increased risk of abdominal wall defects such as omphalocele (24). Water chlorination does not appear related to abdominal wall defect (33).
One study found that maternal smoking is not associated with omphalocele (63). However another study found a moderately elevated risk for omphalocele in women who are heavy smokers and who used alcohol during the first trimester of pregnancy (37).
The use of antibiotics or benzodiazepines do not seem to be a risk factor for omphalocele (18, 19, 20, 21, 25). Antibiotics are used to treat bacterial infections and benzodiazepines (ben-zo-dye-AZ-a-peens) are a class of drugs used to treat such things as insomnia and anxiety.
There is some evidence that Selective Serotonin Reuptake Inhibitors (SSRIs) in early pregnancy may increase the risk of omphalocele (1). But at least oen study did nto find that risk (30). SSRIs are medications used to treat depression.
Misoprostol is not associated with a risk of omphalocele (46). Misoprostol is a drug mainly used to treat stomach ulcers but may also induce labor and induce abortion in elective terminations.
Taking multivitamins that contain folic acid before and during pregnancy may help prevent omphalocele. (5,45). However, this evidence is mixed as some studies have found no effect of taking folic acid on reducing the risk of omphalocele (16, 17). Folic acid is very important in preventing other types of birth defects.
Other Risk Factors
Being poor may increase the risk of having a baby with omphalocele (65), and mothers who work in service work may have a slightly higher risk for omphalocele compared to homemakers and farmers' wives (28).
What is the treatment for omphalocele?
The treatment and outcome for a baby with omphalocele depends on what other health problems it has. Omphalocele is often occurs with other birth defects and other developmental problems like low birth weight. Parents and their doctor must determine the best treatment for each child.
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