Maternal Fluids Linked to Excess Weight Loss in Breast-Fed Newborns

Nancy Fowler Larson

December 22, 2010

December 22, 2010 — Excess weight loss (EWL) in breast-fed newborns is more common than previously believed and is associated with maternal fluid intake during childbirth, according to a study published online December 20 in the journal Pediatrics.

Defined as a loss of 10% or more of birth weight, EWL has a known relationship with delayed lactogenesis and poor infant breast-feeding behavior. Smaller studies have found that long labor, pain medication in second or subsequent labors, and a lack of oxygen treatment for newborns are also EWL contributors.

"Objectives of this larger study were to describe weight loss in a diverse population of first-born, predominantly breastfed infants and to evaluate potentially modifiable risk factors for EWL," write Caroline Chantry, MD, from the Department of Pediatrics, at the University of California–Davis Medical Center in Sacramento, and colleagues.

The prospective study involved 448 multiethnic pregnant women receiving prenatal care at the University of California–Davis Medical Center between January 2006 and December 2007. Each woman was between 32 and 40 weeks of gestation with a single pregnancy. Those with high-risk medical conditions, with an inability or refusal to breast-feed, or who were younger than 19 years with no parental consent were excluded.

Research assistants visited the mothers within 24 hours after birth to gather information regarding a variety of factors: labor, deliver, interventions, outcomes, breast-feeding behaviors and difficulties, use of formula and pacifiers, nipple type, and pain and lactogenesis onset. Delayed lactogenesis was defined by breasts not feeling "noticeably fuller" 72 hours postpartum.

The investigators gathered information about intrapartum fluid intake using electronic medical records. Fluid levels were measured by subtracting urine output from the total amount of fluid taken either intravenously or orally during the intrapartum period, and dividing that figure by the number of hours of hospital labor.

Breast-feeding was observed and rated with the Infant Breastfeeding Tool. Infants were weighed on days 3 and 7.

To assess the relationships of demographic and clinical data with EWL, the investigators used bivariate analyses with χ2 tests. Logistic regression evaluations were used to assess independent associations with EWL in both theoretical and traditional empirical models. These included all variables related to EWL in bivariate analyses (unadjusted P < .10).

Some Cases of EWL May Only Represent Loss of Excess Fluids

The results showed that 18% of the infants with no or minimal formula intake (≤60 mL total since birth) experienced EWL (n = 229). That percentage includes 19% of exclusively breast-fed (EBF) infants (n = 134) and 16% of those who ingested minimal formula (n = 95).

The researchers noted that the 18% incidence of EWL is "alarmingly high" — nearly double that found for first-born infants in a study published in the Journal of Pediatrics in 2001.

Other significant findings were as follows:

  • EWL incidence was not statistically different for EBF newborns and those receiving minimal formula (P = .56);

  • EWL was linked in bivariate analyses to greater maternal age, education, and income; hourly intrapartum fluid balance; edema after delivery; later lactogenesis; fewer infant stools; and infant birth weight (P < .05);

  • After multivariate logistic regression analysis, EWL was significantly predicted by 2 variables: intrapartum fluid balance (adjusted relative risk for EWL of 3.18 [95% confidence interval (CI), 1.35 - 13.29] and 2.80 [95% CI, 1.17 - 11.68] with net intrapartum fluid balance of >200 and 100 - 200 mL/hour, respectively, vs <100 mL/hour) and delayed lactogenesis (adjusted relative risk, 3.35 [95% CI, 1.74 - 8.10]).

"We postulate that weight loss associated with positive maternal fluid balance represents loss of excess fluid in the newborn, but caution must be exercised because this weight loss might represent loss of 'true' weight through inadequate nutrition," the authors write.

The investigators acknowledged several limitations to their study, including the following:

  • because the infants' weights were determined at between 70 and 98 hours postpartum, the incidence of EWL is likely higher than shown;

  • an all-EBF cohort may have resulted in a greater prevalence of EWL;

  • timely day 3 weight data were only available for 70% of the infants;

  • a single, random Infant Breastfeeding Tool score may have been insufficient for rating breast-feeding; and

  • detection of a relationship between EWL and labor pain management was hampered by the fact that 9% of mothers received no pain medications during labor.

Further research is necessary before drawing any firm conclusions about EWL in the presence of excess maternal fluid.

"Because EWL may carry a greater risk of subsequent morbidities, increased attention to preventive strategies is indicated," the authors write.

The US Department of Health and Human Services supported the study. The study authors have disclosed no relevant financial relationships.

Pediatrics. Published online December 20, 2010.

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