Even though doctors often tell parents that newborns will regain weight lost after birth within a week or two, many infants take much longer to achieve this milestone, a U.S. study suggests.

Nearly all newborns lose weight during the first days after birth, regardless of whether they are breastfed or formula fed. Many doctors expect babies to regain those lost ounces and surpass their birth weight within 10 to 14 days.

But by 14 days, 14 percent of babies born vaginally and 24 percent of infants delivered via cesarean section surgeries didn’t return to their birth weight, the study of almost 144,000 newborns found.

“It is normal for newborns to lose a significant amount of weight in the first 1 to 3 days after delivery due to both urinating excess fluid and limited intake,” said lead study author Dr. Ian Paul, a researcher at Penn State College of Medicine in Hershey, Pennsylvania.

C-section babies may lose more weight after birth because they come into the world more hydrated than other infants due to intravenous fluids given to women prior to and during the surgery, Paul added by email.

“Upon birth, the newborn weighs relatively more after a C-section and has therefore more fluid to urinate out resulting in greater relative weight loss,” Paul said.

The American Academy of Pediatrics suggests that most newborns should surpass their birth weight by the time they are 7 to 10 days old, with weekly gains of 4 to 7 ounces for the first several months of life.

For the current study, researchers examined data on babies delivered at Kaiser Permanente Northern California Medical Centers between 2009 and 2013. All of the babies were born at or near full term and had a healthy weight at birth.

Half of the newborns were at or above their birth weight at 9 and 10 days after vaginal and cesarean deliveries, respectively, researchers report in Pediatrics.

After 21 days, however, 5 percent of babies with vaginal births and 8 percent of infants with cesarean deliveries still weren’t back to their birth weights, the study also found.

One limitation of the study is that researchers lacked data on how infants were fed once they went home from the hospital, which can influence the amount of weight they gain, the authors note.

Even so, the findings should be reassuring to parents of babies that don’t return to their birth weight within 7 to 10 days, said Tessa Crume, a researcher at the Colorado School of Public Health in Aurora who wasn’t involved in the study.

In particular, women who breastfeed should take these results as a reason not to panic, Crume added by email.

“For families who want to breastfeed, this is important reassurance that slower regain of infant birth weight does not signal inadequate maternal breast milk supply, but rather a normal newborn growth pattern,” Crume said.

To increase the odds that breastfed babies will gain enough weight, though, women should focus on eating a healthy diet high in fruits, vegetables and healthy fats while they are pregnant and breastfeeding, Crume added by email.

Women can also increase their milk production by starting to breastfeed as soon as possible after delivery or by pumping breast milk, said Dr. Sarbattama Sen, a researcher at Harvard University and Brigham and Women’s Hospital in Boston.

While parents shouldn’t necessarily worry when babies don’t regain their birth weight quickly, they should still watch for potential signs of trouble such as dehydration, inactivity, low urine or stool output and jaundice, Sen, who wasn’t involved in the study, added by email.

“Parents whose infants have not regained birth weight by 7-10 days should continue to be closely monitored by healthcare providers,” Sen said.

As long as babies get these checkups, slow and steady weight gain – even if it’s slower than current guidelines suggest – may be just fine, said Dr. Charles Wood of the University of North Carolina at Chapel Hill.

“This study will help clinicians and parents reframe expectations around adequate weight gain in early life,” Wood, who wasn’t involved in the study, said by email.

Source: Reuters