For preterm babies, delaying umbilical cord clamping after birth reduces the risk of mortality by around 30% in comparison with immediate cord clamping, according to a new meta-analyses published in The Lancet.
Researchers also assessed the efficacy of cord milking, the practice of pumping blood to the baby through the cord, and found no statistically significant improvement in the rate of deaths before discharge compared to immediate or deferred cord clamping.
Dr Anna Lene Seidler
While a large body of research shows that deferred cord clamping and cord milking improve infant survival rates, until now, researchers had not reached a clear consensus on which strategies work best, according to Anna Lene Seidler, PhD, senior research fellow at the Clinical Trials Center of the National Health and Medical Research Council at the University of Sydney in Australia.
“We brought together this really large database to be able to ask the question, ‘What actually works best? How can we improve survival for preterm infants?’ ” Seidler, the lead author of both studies, said.
Previous studies have shown that waiting to clamp the umbilical cord improves circulation, increases iron storage, and lowers rates of brain bleeding.
Dr Ilina Pluym
“But to show a decrease in overall mortality is impressive,” said Ilina Pluym, MD, assistant clinical professor of obstetrics and gynecology at the David Geffen School of Medicine at University of California, Los Angeles. Although “before practice change can be recommended widely, I would want to see the results repeated among a broader general population.”
In 2022, 1 in 10 babies in the United States were born preterm. The rate of infant mortality due to prematurity or low birthweight was 87.1 per 100,000 live births in 2020.
The American College of Obstetricians and Gynecologists (ACOG) recommends deferring cord clamping for 30 to 60 seconds for preterm infants. This guidance was last updated in 2023 and was based on a review of relevant new evidence. Mark Turrentine, MD, chair of the Clinical Consensus Committee for Obstetrics at ACOG, said their committee also considers guidelines from other organizations and federal agencies during the process and typically publishes an update every 3 years.
“In some cases, important new studies or other developments may trigger an earlier review; revisions may be made if there is new evidence-based research or data that would lead to additional or revised recommendations,” Turrentine said. He said the committee will review the two new studies.
The first analysis examined 48 trials of cord milking, immediate clamping, or deferred clamping. The trials included more than 6367 infants (roughly 55% male, 45% female) from 18 countries, including the United States.
Deferred clamping, defined as waiting at least 15 seconds, reduced death before discharge by around 30% compared with immediate clamping (odds ratio [OR], 0.68; 95% CI, 0.51 – 0.91) among 3260 infants. There were 232 deaths in 20 trials. The certainty of evidence was high, according to study authors. No statistically significant differences were found in rates of death before discharge between the other two groups, likely owing to small sample sizes, according to the authors.
Both deferred clamping and milking were associated with a reduced need for blood transfusion. Deferred clamping cut the need for blood transfusions by 41% compared to immediate clamping. Milking reduced it by 31%. These results support the hypothesis that both practices increase the amount of blood babies receive from the placenta, the researchers wrote.
“Over the last couple of years, it has become standard practice to perform delayed cord clamping of between 30 to 60 seconds,” Pluym said. But it “probably does vary for hospitals by C-section or vaginal delivery and term vs preterm.”
Another analysis was conducted of 47 trials with 6094 participants from 28 countries, including the United States. This study sought to reveal the optimal amount of time to wait before clamping the umbilical cord. Three periods of deferral were assessed: short (15 to 45 seconds), medium (45 to 120 seconds), and long (120 seconds or more).
The best outcomes were associated with long deferral, which reduced rates of death before discharge by 70% (OR, 0.31; 95% CI, 0.11 – 0.80). The degree of certainty was moderate, according to the authors.
“I’m surprised that the additional time was that much more beneficial,” said Pluym. “I would think that the majority of the benefits would come from within a minute.”
She said that in her clinical experience, she finds that most of the blood transfer occurs within the first minute before clamping the cord, which falls within current ACOG guidelines.
All infants were delivered in hospitals with neonatal intensive care units, because deferring cord clamping can require oxygen ventilation or resuscitation. Preterm infants are also at risk of developing hypothermia, Seidler said. Best practices for deferred cord clamping include drying and wrapping the infant and having a bedside resuscitation trolley nearby with a way to provide oxygen ventilation, she said.
The findings, therefore, are only applicable to settings with neonatal units and resources to keep infants alive during the delay, said Seidler.
“Deferring cord cutting does not mean just standing there and waiting,” said Seidler. “It means caring for the baby in the first couple of minutes after birth, and that requires training; it requires multidisciplinary teams that may require the right equipment.”
Both meta-analyses were funded by the Australian National Health and Medical Research Council. The authors report iCOMP trial representatives were principal investigators of studies included in this meta-analysis. Trial representatives did not contribute with regard to study eligibility, data integrity assessments, data extraction, or risk of bias assessments for their own studies. Trial representatives did not make final decisions on certainty of evidence ratings. The original article has a full list of the authors’ relevant financial relationships.
Brittany Vargas is a medicine, mental health, and wellness journalist.
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