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