5.4 Cord Clamping, Cord Blood, Cord Gases & Placental Examination
Key Takeaways
- ACOG recommends delaying cord clamping at least 30 to 60 seconds in vigorous term and preterm newborns, improving infant iron stores through 4 to 6 months and reducing intraventricular hemorrhage and necrotizing enterocolitis in preterm infants.
- Umbilical cord milking is not recommended below 28 weeks because trials showed increased severe intraventricular hemorrhage.
- Umbilical arterial blood is the fetal sample and has a lower pH and higher pCO2 than venous blood; nearly identical paired values usually mean both were drawn from the vein.
- Metabolic acidemia consistent with an acute intrapartum hypoxic-ischemic event is an umbilical arterial pH below 7.00 with a base deficit of 12 mmol/L or greater.
- Fetal-surface vessels that run to the membrane edge and stop abruptly indicate a retained succenturiate lobe, and a single umbilical artery occurs in 0.5 to 1 percent of births and is associated with renal and cardiac anomalies.
Timing of Cord Clamping
For most of the twentieth century the umbilical cord was clamped within seconds of birth. Current practice reverses that default.
ACOG recommends delaying umbilical cord clamping for at least 30 to 60 seconds after birth in vigorous term and preterm infants. WHO recommends not less than one minute. Many midwives wait until cord pulsation ceases in a vigorous term newborn.
| Population | Documented Benefits of Delayed Clamping |
|---|---|
| Term newborns | Higher hemoglobin at birth; improved iron stores through 4 to 6 months, which matters because iron deficiency in infancy is linked to impaired neurodevelopment |
| Preterm newborns | Improved transitional circulation and blood pressure, less intraventricular hemorrhage, less necrotizing enterocolitis, and reduced need for blood transfusion |
The trade-off: a modest increase in the proportion of term infants requiring phototherapy for hyperbilirubinemia. This is managed with bilirubin surveillance, not by abandoning the practice.
When to clamp immediately: a newborn who requires resuscitation and cannot receive it at the bedside, maternal hemodynamic instability or hemorrhage, placental abruption, placenta previa with bleeding, vasa previa, or a cord avulsion.
Umbilical cord milking is an alternative when immediate clamping is otherwise required, but it is not recommended below 28 weeks because trials showed increased severe intraventricular hemorrhage.
Umbilical Cord Blood Collection
Clinical cord blood is drawn from the umbilical vein after clamping for newborn ABO and Rh type and a direct antiglobulin (Coombs) test whenever the mother is Rh-negative or has an atypical antibody, and for newborn blood typing where locally indicated.
Cord blood banking requires antenatal counseling and consent, and the midwife should be able to explain the difference:
- Public banking: donated at no cost, made available to any matched recipient and to research. Professional organizations favor public donation.
- Private (directed) banking: stored for the family for an annual fee. The probability that a healthy child will use their own stored unit is very low, and autologous units cannot be used for genetic disease already present in that child. Directed sibling banking is genuinely indicated when a sibling has a condition treatable by transplant.
- Collection must not compromise delayed cord clamping, which takes priority.
Umbilical Cord Gases
Paired cord gases document the fetal acid-base status at the moment of birth and are the objective counterweight to a subjective Apgar score.
Technique. Immediately after birth, doubly clamp a 10–20 cm segment of cord. Draw paired arterial and venous samples into heparinized syringes, expel air, and cap them. A clamped segment remains valid for roughly 60 minutes at room temperature.
| Value | Typical Term Arterial Range | Typical Term Venous Range |
|---|---|---|
| pH | ~7.18–7.38 (mean ≈ 7.27) | ~7.25–7.45 (mean ≈ 7.34) |
| pCO2 | ~40–60 mmHg | ~30–45 mmHg |
| Base deficit | <12 mmol/L | <12 mmol/L |
[!IMPORTANT] The artery is the fetal sample. Umbilical arterial blood is returning from the fetus and has the lower pH and higher pCO2; venous blood is coming from the placenta. If the two samples are nearly identical, both were probably drawn from the vein and the result cannot be interpreted as fetal status.
Metabolic acidemia severe enough to be consistent with an acute intrapartum hypoxic-ischemic event is defined as an umbilical arterial pH below 7.00 with a base deficit of 12 mmol/L or more.
When to obtain gases: cesarean birth for fetal compromise, a low 5-minute Apgar score, severe fetal growth restriction, an abnormal fetal heart rate tracing, intrapartum fever, thick meconium, multifetal gestation, and any birth followed by neonatal depression or resuscitation.
Examining the Cord and Placenta
The Umbilical Cord
- Count the vessels: two arteries and one vein is normal. A single umbilical artery occurs in about 0.5–1% of births and is associated with renal, cardiac, and chromosomal anomalies; it warrants newborn examination and consideration of renal imaging.
- Note length (normal ≈ 50–60 cm), true knots, nuchal or body cords, and insertion site — a velamentous or marginal insertion is associated with vasa previa, growth restriction, and cord compression.
Mechanism of Placental Delivery
- Schultze mechanism ("shiny Schultze"): the placenta separates centrally, inverts, and delivers fetal surface first — the glistening amnion appears at the introitus. Bleeding is concealed behind the placenta until it delivers.
- Duncan mechanism ("dirty Duncan"): the placenta separates at its margin and delivers maternal surface first — the dull, red, cotyledon-covered side appears. Bleeding is visible earlier and blood loss tends to be greater.
Systematic Placental Inspection
- Maternal surface: lay it out and confirm that all cotyledons are present and fit together. A missing cotyledon means retained tissue — the cause of secondary postpartum hemorrhage and endometritis. Note infarcts, calcifications, and adherent retroplacental clot suggesting abruption.
- Fetal surface: inspect the vessels running to the cord insertion. Vessels that run to the membrane edge and end abruptly indicate a torn succenturiate lobe retained in the uterus.
- Membranes: reconstruct the sac and confirm both amnion and chorion are complete; note green staining (meconium), opacity or odor (infection).
- Weight and appearance: the term placenta weighs roughly one sixth of the newborn's weight.
- Document completeness, cord vessel count, insertion, and any abnormality in the birth note.
When to Send the Placenta to Pathology
Send the placenta fresh and unfixed for stillbirth or neonatal death, preterm birth, severe growth restriction, maternal fever or suspected intraamniotic infection, abruption, hydrops, thick meconium with neonatal depression, cord acidemia or a low 5-minute Apgar, suspected placenta accreta spectrum, abnormal cord findings, and multifetal gestation.
After a term birth complicated by a prolonged deceleration, paired umbilical cord gases return as follows: sample A pH 7.31, pCO2 42 mmHg; sample B pH 7.32, pCO2 40 mmHg. How should these results be interpreted?
While inspecting the placenta after a spontaneous vaginal birth, the midwife notes that the maternal surface appears complete but several fetal-surface vessels run toward the membrane edge and terminate abruptly at a torn area. What does this finding indicate and what is the appropriate action?