Post-Dated (Postterm) Pregnancy

Definition & Terminology

• Postterm pregnancy: Pregnancy continuing beyond 42 weeks (294 days) of gestation
• "Post-dates" is a misleading/imprecise term — some interpret it as simply going past the EDC (40 weeks); "postterm" is the preferred nomenclature
• "Late-term" = 41 0/7 to 41 6/7 weeks
• Incidence: ~7–12% of pregnancies

Dating of Pregnancy

• Nägele's Rule: Subtract 3 months from LMP + add 7 days = EDC
• EDC should ideally be confirmed by ultrasound before 22 weeks
  • ≤ 12 weeks: margin of error ± 7 days
  • 12–20 weeks: ± 14 days
• Most postterm pregnancies are due to inaccurate EDC calculation

Risk Factors

Complications

Maternal Complications

• Labor dystocia
• 3rd and 4th degree perineal lacerations
• Postpartum hemorrhage
• Maternal infection (intra-amniotic infection, endometritis)
• Increased risk of cesarean section

Fetal/Neonatal Complications

• Macrosomia (large for gestational age)
• Intrauterine fetal demise (risk increases as pregnancy progresses)
• Meconium aspiration syndrome
• Decreased 5-minute Apgar score (< 4)
• Neonatal convulsions
• Note: Umbilical cord prolapse is NOT increased; amniotic fluid volume actually decreases

Dysmaturity Syndrome (Clifford Syndrome)

• Affects 10–20% of postterm pregnancies
• Cause: uteroplacental insufficiency (chronic intrauterine malnutrition)
• Infant features: meconium stained, small for gestational age, peeling (desquamating) skin
• Neonatal risks: respiratory distress from meconium aspiration, hypoglycemia, neonatal seizures, cerebral palsy

Antepartum Surveillance

• Begin at 41 weeks
• Twice-weekly NST, BPP, or both

Biophysical Profile (BPP) — 5 Elements (each scored 0 or 2; total = 10)

• BPP 8–10 = Normal | 6 = Equivocal | 0–4 = Abnormal
• Modified BPP = NST + AFI (acceptable alternative)

Reactive NST Criteria

• ≥ 32 weeks: 2 accelerations of ≥ 15 bpm lasting ≥ 15 sec in a 20-min window
• < 32 weeks: 2 accelerations of ≥ 10 bpm lasting ≥ 10 sec

Management / Induction of Labor

• Induction can begin electively at 41 weeks or as surveillance dictates
• ACOG recommends induction before 42 6/7 weeks' gestation
• Use Bishop score (< 6 per AAFP; < 8 per ACOG) to determine need for cervical ripening

Bishop Score

Cervical Ripening Methods

• Intrauterine Foley catheter
• Cook double balloon
• Osmotic dilators (laminaria)

• Vaginal misoprostol (Cytotec) 25 mcg q4h
• Dinoprostone (Cervidil) 10 mg insert × 12h; or Prepidil gel 0.5 mg q6h × 3 doses

Dystocia (Abnormal Labor)

Definition

• Accounts for 1/3 of all cesarean sections and 1/2 of primary cesarean sections
• The term "failure to progress" is vague and should NOT be used — use specific terminology instead

The 3 P's — Causes of Dystocia

Dystocia is usually caused by a combination of these factors.

Stages of Labor — Normal Limits

Types of Labor Arrest

1. Arrest of Dilation (First-Stage Arrest)

• No cervical change despite:
  • 4 hours of adequate contractions (≥ 200 Montevideo units/10 min by IUPC), OR
  • 6 hours of oxytocin augmentation with inadequate uterine activity + no cervical change
• Most common indication for primary cesarean section in the US
• Allowing 4 hours of arrest (rather than 2 hrs) before resorting to cesarean results in successful vaginal delivery in most women with no adverse neonatal effect

2. Arrest of Descent (Second-Stage Arrest)

• No descent after adequate pushing beyond the time limits above
• Longer durations may be considered if progress is documented and maternal/fetal status is reassuring

Key Diagnostic Tool: Montevideo Units (MVUs)

• Measured by intrauterine pressure catheter (IUPC)
• External tocometer measures only frequency, not amplitude
• ≥ 200 MVUs in 10 minutes = adequate contractions → increased oxytocin is of no benefit
• < 200 MVUs = augment with oxytocin

Management of Labor Dystocia

• Oxytocin augmentation — mainstay for inadequate uterine activity
• IUPC placement — to accurately measure contraction strength
• Ambulation — often encouraged but NOT shown to resolve active-phase arrest
• Operative vaginal delivery (forceps/vacuum) — option only in 2nd stage
• Cesarean section — for confirmed arrest unresponsive to augmentation

Malpresentations — Incidence

Shoulder Dystocia

Incidence

• Overall: 0.3–1%
• With macrosomia (birth weight > 4500 g): 5–7%
• ~50% occur with normal-weight fetuses and are unanticipated

Risk Factors

• Macrosomia / maternal diabetes
• Maternal obesity / prepregnancy weight > 180 lb
• Excessive weight gain
• Advanced maternal age
• Postterm pregnancy
• Prior shoulder dystocia
• Contracted pelvis
• Prolonged 2nd stage / operative vaginal delivery

Warning Signs

• Prolonged 2nd stage
• Use of vacuum or forceps

Complications

• Brachial plexus injury — most common
  • Erb's palsy (C5–C6) — most common
  • Klumpke's palsy (C8–T1)
• Clavicular fracture
• Fetal hypoxia → neurological damage, death

Management — HELPERR Mnemonic

⚠️ Fundal pressure is contraindicated — it worsens shoulder impaction.