About Discordant Fetal Growth
Discordant fetal growth is a condition that can affect any pregnancy carrying multiple babies. Though the causes are still not well understood, the need for relevant research continues to grow as discordance is becoming a more widespread problem with the increase in multiple births; twin discordance increased 25 percent among twin pregnancies after the use of assisted reproductive technologies, according to Lippincott's Nursing Center.
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Definition
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Discordant fetal growth refers to a significant birth weight difference between twins or other multiples. The weight difference must be at least 15 percent to be considered discordant although it can range to even greater than 30 percent, according to Lippincott's Nursing Center. Multiples with congenital or chromosomal anomalies are not included in the definition of discordant multiples, nor are babies affected by twin-to-twin transfusion syndrome. Most of the existing research on discordant fetal growth refers to discordant twins because twin births are far more common than other multiples.
Incidence
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According to the March of Dimes organization, the number of twin births increased from 25.9 to 32.1 per 1000 live births from 1996 to 2006. This is mainly due to increased multiple births that result from assisted reproductive technologies; as of 2005, 16 percent of U.S. twins born are conceived by ART, according to Lippincott's Nursing Center. Growth restriction is more common among twins, making the understanding of discordant fetal growth increasingly important to both health professionals and families across the U.S. Birth weight discordance occurs in 10 to 15 percent of twin pregnancies, according to Lippincott's Nursing Center.
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Cause
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The causes of discordant fetal growth are not always clear and can sometimes be attributed to more than one factor. Possible causes include blood flow issues, genetic potential, sex of the fetus, environmental factors, and genetic predisposition of the smaller twin to low birth weight that is further complicated by either the crowded growing environment or a placental insufficiency.
Effects
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According to a study of discordant twins published in Advances in Neonatal Care, larger twins had more acute respiratory problems but were discharged from hospital care earlier than smaller twins because they were quicker to achieve important milestones and with fewer complications. Smaller twins showed less respiratory disease and good catch-up growth but were slower to reach the milestones necessary for hospital discharge. Only 33 percent of twins were discharged on the same day, according to Lippincott's Nursing Center.
Dangers
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Discordant fetal growth among twins is a significant contributor to perinatal morbidity and mortality rates. When weight discordance between multiples is 20 percent or more, there is a significant increase in complications, according to Lippincott's Nursing Center, and a 30 percent discordance among preterm twins is associated with a 25 percent increase in death rates. Most, but not all, deaths occur in the smaller twin.
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