Twins rarely weigh the same amount at birth, but often both babies will weigh within a few ounces of one another. In some cases, one twin may be significantly smaller or larger than their sibling.
Researchers have found a connection between significant weight differences in twin births and health complications later in life.
More than 1,000 women participated in the twin birth weight study. Pregnancies ended in twin live births between 2007 and 2009. In cases where the gap between twin weights measured 18-percent or more, the infants were at increased risk of health complications and infant mortality. Twins weighing differing amounts are called discordant twins. The smaller of the twins was once thought of as the twin most at-risk for health problems, but this research study noted that both twins in a discordant pair are at increased risk.
There is little that can be done to control twin weight in utero, but close monitoring can give doctors an idea of current weight. If weight is monitored closely, doctors will notice a significant difference if one were to occur.
According to Dr. Fionnuala Breathnah obstetrician and lecturer, “Recognition of this [18-percent] threshold difference in weight during pregnancy should trigger closer fetal monitoring and in some circumstances may prompt early delivery.” In many cases, women pregnant with multiples undergo more ultrasounds than women pregnant with singlets. Ultrasounds give doctors a close look at development. Weight can also be measured during ultrasound.
While C-sections have come under scrutiny in the past few years, researchers believe one of the viable options to reduce health risks for discordant twins is early birth. Doctors can choose to initiate labor or plan a C-section before weight differences increase or additional problems arise.
More research is needed with a larger participant group to determine if early birth increases or decreases risk of complication.

Source: Dr. Fionnuala Breathnah. Royal College of Surgeons in Ireland. 9 May, 2011.

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