What is meconium?
Meconium is the baby’s first stool, or poop. It is sticky, thick, and dark green, almost black in color. Meconium starts forming in the intestines around the 12th week of pregnancy. It’s made up of things babies ingest in the womb: amniotic fluid, skin cells, lanugo (fine hair), bile, water, and mucus. Meconium builds up in the intestines and is stored there until after birth.
Meconium is sterile until after birth. It’s passed after birth once feeding starts, and the colon responds to earth’s gravity and contractions. On average, meconium is passed within 48 hours of birth. However, sometimes meconium can be passed before birth inside the amniotic sac, which can potentially cause health complications.
When is meconium passage concerning?
Meconium passage before birth occurs in around 10-15% of all births. It becomes concerning when meconium-stained amniotic fluid (MSAF) is present. MSAF occurs when the fetus passes meconium in utero and mixes with the amniotic fluid. This results in staining of the fluid.
MSAF can occur at any time during pregnancy but is more common after 34 weeks gestation. The timing of meconium passage determines the associated risks. Early passage, before 34 weeks, is likely a sign of fetal distress. Late passage, after 34 weeks, is more common and less concerning.
Causes of meconium passage before birth
Some potential causes of MSAF include:
- Fetal distress – Lack of oxygen can cause relaxation of anal sphincter
- Post maturity – After 42 weeks gestation, meconium passage risk increases
- Infection – Inflammation from infection can stimulate bowel movement
- Drug use – Tobacco, cocaine, methamphetamine use is associated with MSAF
- Placental abnormalities – Reduced blood flow to fetus can lead to distress
- Umbilical cord issues – Cord compression or tight nuchal cord can reduce oxygen
- Maternal hypertension – High blood pressure reduces placental perfusion
- Intrauterine growth restriction – Poor growth and reduced oxygenation
- Oligohydramnios – Low amniotic fluid volume concentrates meconium
Identifying the cause of MSAF allows providers to monitor the fetus and prepare for potential complications after birth.
Risks of meconium aspiration syndrome
The main risk associated with meconium passage before birth is meconium aspiration syndrome (MAS). This occurs when the newborn inhales meconium-stained amniotic fluid into the lungs during labor and delivery.
Meconium is very irritating to the lung tissue and can cause breathing problems by:
- Blocking the airways
- Damaging the lungs
- Triggering inflammation and infection
MAS can lead to serious respiratory complications after birth and affect the newborn’s transition to life outside the womb. Around 5-10% of newborns with MSAF will develop MAS. Of those with MAS, 2-9% will die from meconium aspiration complications.
Risk factors for meconium aspiration syndrome
Certain situations increase the risk of a newborn developing MAS:
- Thick meconium – Harder to clear from airways
- Premature birth – Lungs not fully developed
- Postmaturity – Meconium passage more likely
- Breech position – Difficulty clearing fluid
- Nuchal cord – Compresses umbilical cord and reduces oxygen
- Respiratory distress – Difficulty establishing breathing
- Low apgar score – Poor transition to newborn life
Identifying these risk factors allows the birth team to prepare for resuscitation measures in case the newborn has breathing troubles.
How does meconium affect the mother during delivery?
The main way meconium affects the mother during labor and delivery is by increasing her chance of developing a postpartum infection. Meconium passage in-utero is a sign that the amniotic sac has been ruptured for a prolonged time. This allows bacteria to ascend into the uterus and raises the risk of chorioamnionitis and endometritis after delivery.
Chorioamnionitis
Chorioamnionitis is an infection of the amniotic sac and fluid (chorioamnion). It occurs more often when meconium is present. Signs of chorioamnionitis include:
- Fever >100.4F
- Foul smelling amniotic fluid
- Tenderness of uterus
- Maternal tachycardia >100 bpm
- Fetal tachycardia >160 bpm
Chorioamnionitis increases the mother’s risk of postpartum hemorrhage, sepsis, and other infectious complications. It is treated with antibiotics,labor augmentation, and immediate delivery.
Endometritis
Endometritis is an infection of the uterine lining (endometrium) that also occurs more frequently with meconium. Symptoms include:
- Fever >100.4F
- Foul lochia
- Uterine tenderness
- Tachycardia >100 bpm
It is typically diagnosed 24-48 hours after delivery. Risk factors include prolonged labor, prolonged rupture of membranes, and multiple vaginal exams. Endometritis is treated with IV antibiotics.
How should labor be managed when meconium is present?
When meconium-stained fluid is identified, specific steps should be taken:
- Notify pediatric team for potential MAS resuscitation
- Consider amnioinfusion to dilute meconium if fetal heart tracing reassuring
- Do not perform digital cervical exams to avoid introducing meconium into uterus
- Avoid early artificial rupture of membranes unless indicated
- Monitor for signs of chorioamnionitis and treat appropriately
- Clamp cord earlier and hand off to pediatric team for suctioning
In some cases, the provider may recommend induction of labor or cesarean delivery for poor fetal heart tracings or thick meconium. Close monitoring throughout labor is key to reducing complications.
What is amnioinfusion?
Amnioinfusion is a procedure where sterile fluid is infused into the uterus during labor. It can be used to dilute thick meconium and reduce the risk of MAS. Saline or Ringer’s lactate solution is infused through an intrauterine pressure catheter in the uterus.
Amnioinfusion has been shown to decrease the risk of MAS. It allows meconium to pass through the fluid more easily. However, there are risks like cord prolapse, maternal fluid overload, and infection. So, it is not routinely recommended as a standard of care and is decided on a case-by-case basis.
What special care does the newborn need after meconium delivery?
Babies born through MSAF require special care immediately after delivery to clear meconium and evaluate breathing:
- Thorough suctioning of mouth and nose before first breath
- Possible intubation and tracheal suction if thick meconium present
- Monitoring oxygen saturation with pulse oximetry
- Blood gas assessment if respiratory distress suspected
- Chest x-ray to evaluate for meconium aspiration syndrome
- Supportive respiratory treatments like oxygen, CPAP, or mechanical ventilation
- Antibiotics if infection suspected
With close monitoring and respiratory support, most babies recover well even if some meconium is inhaled. However, in severe cases, ECMO oxygenation may be needed if the lungs are significantly damaged.
| Intervention | Purpose |
|---|---|
| Suctioning | Clear meconium from airways |
| Oxygen monitoring | Assess oxygenation and need for support |
| Blood gases | Evaluate respiratory status |
| Chest x-ray | Diagnose meconium aspiration syndrome |
| Respiratory support | Manage MAS complications |
| Antibiotics | Treat suspected infection |
What is the long term prognosis after meconium aspiration syndrome?
Most infants who suffer MAS recover fully, especially if identified and treated early. However, some may experience long-term consequences:
- Recurrent respiratory infections
- Wheezing, asthma, reactive airway disease
- Respiratory syncytial virus (RSV) bronchiolitis
- Airway hyperreactivity and decreased pulmonary function
- Hypoxemia
A small percentage may develop severe lung disease like pulmonary fibrosis, pulmonary hypertension, or cor pulmonale. Risk factors for long-term issues include need for mechanical ventilation, oxygen therapy beyond 2 days old, severity of chest x-ray findings, and pneumonia development.
Follow up after discharge involves monitoring oxygen saturations, pulmonary function, and signs of respiratory distress to identify those needing further pulmonary care. Most complications resolve by 1-2 years old. But some children require asthma medications for ongoing reactive airways.
Conclusion
Meconium passage before birth puts newborns at risk for meconium aspiration syndrome. It also raises the risk of maternal infection during labor and delivery if membranes have ruptured long ago. Careful monitoring and appropriate preparation by the birth team can reduce these risks and improve outcomes. Most complications are short-term and resolve with supportive care. But some infants may experience chronic respiratory issues requiring long-term pulmonary follow up. With modern management, infants with meconium aspiration syndrome generally have an excellent prognosis, especially when identified and treated promptly.