Medical Complications of Post-Term Pregnancy
Post-term pregnancy significantly increases risks of fetal mortality, stillbirth, and neonatal intensive care unit admission, with these risks rising exponentially after 42 weeks' gestation. 1
Definition and Risk Factors
- Post-term pregnancy: pregnancy that has reached or exceeded 42 weeks' gestation
- Late-term pregnancy: 41 weeks 0 days to 41 weeks 6 days' gestation
Maternal Complications
Increased Labor and Delivery Complications
- Higher rates of cesarean delivery due to:
- Fetal distress (observed in approximately one-third of post-term pregnancies) 2
- Cephalopelvic disproportion from continued fetal growth
- Failed induction of labor
Obstetric Complications
- Increased risk of:
- Prolonged labor
- Operative vaginal delivery
- Perineal trauma from macrosomic infants
- Postpartum hemorrhage
- Maternal infection
Fetal and Neonatal Complications
Placental Insufficiency
- Reduced respiratory and nutritive placental function 2
- Increased incidence of placental lesions
- Progressive deterioration of placental function beyond term
Fetal Distress
- Observed in approximately one-third of post-term pregnancies 2
- Increased risk of:
- Meconium-stained amniotic fluid
- Abnormal fetal heart rate patterns
- Fetal hypoxia and asphyxia
Fetal Postmaturity Syndrome (Dysmaturity)
- Characterized by:
- Reduced subcutaneous fat
- Skin desquamation
- Meconium staining of skin, nails, and umbilical cord
- Long nails
- Alert appearance
Macrosomia
- Increased risk of birth weight >4000g 3
- Associated complications:
- Shoulder dystocia
- Birth trauma (brachial plexus injury, fractures)
- Birth asphyxia
Mortality and Morbidity
- Exponential increase in fetal mortality after 42 weeks 1
- Higher rates of:
- Stillbirth
- Neonatal intensive care unit admission
- Meconium aspiration syndrome
- Neonatal pneumonia
- Low Apgar scores
Management Implications
Antepartum Monitoring
- Recommended beginning at 41 weeks' gestation 1
- Includes:
- Non-stress testing
- Biophysical profile
- Amniotic fluid assessment (oligohydramnios increases risk)
Delivery Timing
- Induction of labor at 41 weeks reduces perinatal mortality and stillbirth compared to expectant management 1
- American College of Obstetricians and Gynecologists recommends:
- Considering elective induction at 39 weeks 0 days in low-risk nulliparous patients
- Induction of labor in all patients by 42 weeks' gestation
Intrapartum Considerations
- Careful monitoring of uterine activity
- Lateral positioning of the mother and oxygen supplementation may facilitate fetal oxygenation 2
- Consideration for expedited delivery if signs of fetal compromise develop
Common Pitfalls and Caveats
Inaccurate Dating: The most common reason for post-term pregnancy diagnosis is inaccurate dating. First-trimester ultrasound dating is essential for accurate determination of gestational age.
Delayed Intervention: Waiting too long for spontaneous labor increases risks exponentially after 42 weeks.
Inadequate Monitoring: Insufficient fetal surveillance may miss early signs of placental insufficiency.
Special Neonatal Care Requirements: Postmature infants require specialized neonatal care to address potential complications 2.
Umbilical Cord Management: Delayed cord clamping may be beneficial in postmature infants to counteract potential hypovolemia 2.
The evidence strongly supports active management with induction of labor by 41-42 weeks to reduce the significant risks associated with post-term pregnancy, particularly the exponentially increasing risk of stillbirth and perinatal mortality.