Obstetrics Book

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Post-term Pregnancy

Aka: Post-term Pregnancy, Postterm Pregnancy, Post-dates Pregnancy, Postdates Pregnancy, Late-Term Pregnancy
  1. Epidemiology
    1. True Prevalence of Post-dates Pregnancy: 2-3%
    2. Pseudoprevalence (misdated pregnancy): 10-14%
      1. Inaccurate clinical dating (esp. overestimation) is common if based on Last Menstrual Period (LMP) alone
      2. LMP-based dating assumes accurate recall, regular Menses, no recent OCPs and Ovulation on day 14 of cycle
      3. Most accurate and reliable dates are based on early Ultrasound with Crown-Rump Length
  2. Definition
    1. Late-Term Pregnancy
      1. Gestational age 41 weeks 0 days to 41 weeks 6 days
    2. Post-term Pregnancy
      1. Over 294 days (42 weeks) beyond first day of LMP
    3. Post-Mature Infant
      1. Truly post-term by objective criteria
  3. Risk Factors
    1. Prior Postdates Pregnancy
    2. Nulliparity
    3. Maternal age >30 years old
    4. Obesity
    5. Genetic predisposition
      1. Mother who herself was a product of a Postdates Pregnancy has a 50% risk of Postdates Pregnancy >42 weeks
      2. Morken (2011) BJOG 118(13): 1630-5 [PubMed]
    6. Other causes (rare)
      1. Fetal Anencephaly
      2. Placental surface deficiency
  4. Signs: Physical Characteristics of a post-dates infant
    1. Underweight due to loss of subcutaneous fat
    2. Long and thin in girth
    3. Skin with patchy areas of Desquamation
    4. Skin, long nails may be covered with meconium
    5. Wrinkled hands and feet on ventral surfaces
  5. Complications: Fetal (after 41 weeks gestation)
    1. Perinatal morbidity and mortality increases after 41 weeks gestation (Late-Term Pregnancy)
      1. Nakling (2006) Acta Obstet Gynecol Scand 85(6): 663-8 [PubMed]
      2. Brukner (2008) Am J Obstet Gynecol 199(4): 421 [PubMed]
    2. Meconium Aspiration Syndrome
    3. Neurologic risks (possible)
      1. Seizure disorder (1.2 Incidence rate ratio)
        1. Ehrenstein (2007) Pediatrics 119(3): e554-61 [PubMed]
      2. Cerebral Palsy (1.36 per 1000 compared with 0.99 per 1000)
        1. Moster (2010) JAMA 304(9): 976-82 [PubMed]
  6. Complications: Maternal (after 42 weeks gestation)
    1. Postpartum Hemorrhage
    2. Labor Dystocia
    3. Chorioamnionitis or Endometritis
  7. Management: Approach
    1. Consider sweeping membranes after 38 weeks gestation
      1. Number Needed to Treat to prevent one induction: 8
      2. Associated with Relative Risk of pregnancy beyond 41 weeks: 0.59
      3. Associated with Relative Risk of pregnancy beyond 42 weeks: 0.28
      4. Boulvain (2005) Cochrane Database Syst Rev (1): CD000451 [PubMed]
    2. Informed Consent to continue expectant management beyond 41 weeks
      1. Discuss risks of late-term and Post-term Pregnancy
      2. Discuss risks of Labor Induction and Cesarean Section
    3. Assess for likelihood of induction success
      1. Bishop Score >5-6
      2. Shorter Cervical Length
      3. Lower Body Mass Index
    4. Antenatal surveillance protocol starting at 41 weeks (otherwise low risk pregnancies)
      1. Perform amniotic fluid and Fetal Assessment twice weekly
      2. Amniotic fluid assessment
        1. Amniotic fluid index (AFI) >5 ml or
        2. Amniotic fluid pocket >2 cm x 2 cm fluid pocket
          1. Lack of pocket associated with fetal asphyxia
          2. Lack of pocket associated with perinatal mortality
      3. Fetal Assessment
        1. Nonstress Test reactive or
        2. Contraction Stress Test reactive or
        3. Biophysical Profile 6 or more
  8. Indications: Induction
    1. Oligohydramnois
      1. Amniotic fluid pocket<2 cm single pocket or
      2. Amniotic fluid index < 5ml
    2. Failed Fetal Assessment
      1. Non-reactive Non-Stress Test (with or without confirmatory Biophysical Profile) or
      2. Positive Contraction Stress Test or
      3. Biophysical Profile <6 or
      4. Non-reassuring umbilical artery doppler
    3. Gestational age >41-42 weeks
      1. Fetal mortality reduced for delivery at 41 weeks with NNT 328 to spare one fetal death
        1. Hussain (2011) BMC Public Health 11(suppl 3): S5 [PubMed]
      2. Induction vs expectant management are both reasonable options at 41 weeks
      3. Induction at 41 weeks is associated with a lower Cesarean Section rate
        1. Number Needed to Treat to induce at 41 weeks to prevent one cesarean: 30
        2. Gulmezoglu (2012) Cochrane Dtabase Syst Rev (6): CD004945 [PubMed]
  9. References
    1. Wang (2014) Am Fam Physician 90(3): 160-5 [PubMed]

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