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Baby A or Baby B? Packard Children's policy tracks twins' identities from womb to birth

- By Erin Digitale

Maurice Druzin

Maurice Druzin

The trouble sounds drawn from a Shakespearean plot: Twins’ identities get mixed up; confusion ensues.

But for newborn twins, this scenario is no laughing matter. Many congenital defects of the urinary tract, heart and brain are diagnosed prenatally, and starting treatment immediately after birth can be lifesaving. To make sure twins and higher-order multiples get the right treatments, the newborns must be matched to their prenatal identifiers — Baby A, Baby B, and so on — at birth. That often means breaking with the obstetric tradition of calling the first-born “Baby A.”

“It’s sometimes a little chaotic in delivery,” said Maurice Druzin, MD, the service chief of obstetrics and gynecology at Lucile Packard Children’s Hospital. “If you open the uterus and Baby B pops out first, the OBs have to keep their wits about them and give the correct designation.”

To ensure this happens consistently, the maternal-fetal medicine team at Packard Children’s has introduced an explicit policy of matching infants from multiple-birth pregnancies to their prenatal IDs. In recent years, Druzin, who is also division chief of maternal-fetal medicine at the School of Medicine, noticed that his trainees were reverting to calling the first-born “Baby A.” That was why he and other leaders at the Johnson Center for Pregnancy and Newborn Services felt a new policy was needed.

“The tradition of labeling the first born as ‘Baby A’ comes from the time when we didn’t know anything about the babies prenatally,” said William Benitz, MD, who is division chief of neonatology at Packard Children’s and professor of pediatrics at the School of Medicine. “When I was a resident, we didn’t even know if a baby was a boy or girl until delivery. Now we know a lot about their anatomy before birth.”

Renee Reijo Pera

William Benitz

In prenatal ultrasounds, the baby positioned lowest in the uterus is given the designation of “Baby A.” Under this convention, Baby A will likely be born first in a vaginal delivery. However, about 75 percent of twins are delivered by cesarean section. And, complicating things further, babies sometimes swap positions before birth.

“There is a small but irreducible error rate because babies do switch in utero,” Druzin said. The team sometimes can perform a final ultrasound just before birth to confirm the babies’ positions, but this isn’t possible for every delivery. “However, once we have the expectation that the babies will be designated according to their prenatal identifiers, we can eliminate most of the avoidable errors,” Druzin said.

Instituting the new policy has required educating not just those in the delivery room but also birth recorders at the hospital and county levels. Initially, the birth recorders, used to seeing an earlier delivery time for “Baby A,” questioned birth certificates that did not match the convention. Benitz and Druzin then clarified with the state of California that there is no legal mandate to use identifiers in alphabetical order.

So far, the policy has been a success. The Packard Children’s team, which delivers hundreds of babies from multiple gestations each year, has not had any serious health problems for newborn twins or higher-order multiples resulting from mix-up events, and they aim to keep it that way.

“The most serious error that could occur would be if we said after birth, ‘We looked for that cardiac anomaly and didn’t see it; there must have been a diagnostic error,’ yet the other baby still had the condition,” Benitz said. “So correct alignment is really important.”

Stanford Medicine integrates research, medical education and health care at its three institutions - Stanford University School of Medicine, Stanford Health Care (formerly Stanford Hospital & Clinics), and Lucile Packard Children's Hospital Stanford. For more information, please visit the Office of Communication & Public Affairs site at

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