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This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.

Delays to clamping the umbilical cord of about a minute can reduce hospital mortality for preterm infants by around 32%. Delayed clamping also reduced the proportion of infants needing a blood transfusion by 10%.

This review adds more precise data on survival from new trials including a large Australian trial (over 1,600 babies) to a previous Cochrane 2012 review of trails including 738 infants and provides new more precise data on the survival benefit.

These findings are consistent with current guidelines which recommend delayed clamping in preterm infants.

Why was this study needed?

The optimal timing of umbilical cord clamping has been debated. Globally, around 15 million children each year are born before 37 weeks gestation, and of these around one million do not survive.

Early clamping used to be standard practice for preterm infants due to concerns about potential consequences from any delay to resuscitation, including hypothermia, jaundice, and polycythaemia.

Evidence from a Cochrane review (2012) included 15 studies (738 infants) found that a delay may improve blood pressure, reduce blood transfusions, intra-ventricular haemorrhage, necrotising enterocolitis, and infection. However, there was insufficient data to be confident about any difference to infant mortality that could be the result of enhanced placenta to baby transfusion from delayed clamping.

This review aimed to update the evidence to include all trials completed since 2012 and to provide more precise estimates, particularly for survival.

What did this study do?

This systematic review and meta-analysis included 18 randomised controlled trials comparing delayed (30 seconds or more) versus early (less than 30 seconds) clamping in 2,834 infants. Trials were included if they enrolled infants born at less than 37 weeks’ gestation and their mothers and included a recent large Australian trial. Trials which estimated cord milking in more than 20% of infants in any arm were ineligible. Responses were received from 13 authors confirming no cord milking was used in any arm.

The main outcome measure was all-cause mortality at any time before hospital discharge. Subgroup analyses were performed according to gestational age (28 weeks or less compared with 29-37 weeks), duration of cord clamping, and mode of delivery.

Eighteen trials were included (2,834 infants) from high-income countries, including Scotland Israel and US. Twelve trials were considered at a low risk of bias meaning we can be fairly confident in the results.

What did it find?

  • Overall, delayed clamping reduced all-cause hospital mortality before discharge from hospital (relative risk [RR], 0.68; 95% confidence interval [CI] 0.52 to 0.90).
  • In the three trials (996 infants) at 28 weeks gestation or less, delayed clamping also reduced hospital mortality (RR 0.70, 95% CI 0.51 to 0.95).
  • In two trials, delayed clamping increased peak haematocrit by 2.73% (95% CI 1.94 to 3.52%) and there was less need for transfusion.
  • Potential harms of delayed clamping included a 3% increase in the number of babies with excess red blood cells (polycythaemia) and a slight increase in levels of jaundice.
  • Additional analyses showed that mortality did not vary according to the duration of delay in cord clamping, mode of delivery, or timing of resuscitation.

What does current guidance say on this issue?

The World Health Organisation (2012) states delayed cord clamping (performed 1 to 3 minutes after birth) is recommended for all births, preterm and term, while initiating essential neonatal care. Early umbilical cord clamping (less than 1 minute after birth) is not recommended unless the neonate is asphyxiated and needs to be moved immediately for resuscitation.

The Royal College of Obstetrics and Gynaecology (2015) says that in healthy term babies the evidence supports deferring clamping of the umbilical cord, as this appears to improve iron stores in infancy.

What are the implications?

This review supports current clinical guidelines recommending delayed clamping in preterm infants. It adds more precise data on survival from a large Australian trial which adds over 1,600 babies to a previous Cochrane review of 738 infants.

Using delayed instead of early clamping could potentially save between 11,000 to 100,000 babies globally each year, the researchers say.

Benefits may be greater for some subgroups or periods of delayed clamping. For example, the effects of gestational age were limited by missing data, emphasising the need for individual patient data to inform future, more specific research.

Citation and Funding

Fogarty M, Osborn DA, Askie L, et al. Delayed vs early umbilical cord clamping for preterm infants: a systematic review and meta-analysis. Am J Obstet Gynecol. 2018;218(1):1-18.

This project was funded by Australian National Health and Medical Research Council, and the NHMRC Clinical Trials Centre, University of Sydney.



ACOG. Committee Opinion: Delayed Umbilical Cord Clamping After Birth. Washington: American College of Obstetricians and Gynaecologists; 2017.

NIH. Umbilical cord ‘milking’ improves blood flow in preterm infants. Maryland: National Institutes of Health; 2015.

Royal College of Obstetricians & Gynaecologists. Clamping of the Umbilical Cord and Placental Transfusion. London: Royal College of Obstetricians & Gynaecologists; 2015.

WHO. Guideline: Delayed Umbilical Cord Clamping for improved maternal and infant health and nutrition outcomes. Geneva: World Health Organisation; 2014.

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Peak haematocrit is the proportion by volume of the blood that consists of red blood cells and is expressed as a percentage. Babies born at term usually have a higher hematocrit, compared to older children and adults. It can also be referred to as the retention of blood cells.

Cord milking is a technique which also is also thought to be of benefit during the delivery of preterm infants delivered by caesarean section. It increases the blood flow from the umbilical cord into the infant’s circulatory system, to improve blood pressure and red blood cell levels. The researchers excluded trials of this to avoid confusing the result.


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