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Post-term Pregnancy - Surveillance Strategies. Dr. Yasir Katib MBBS, FRCSC, Perinatologist. Definitions. Post mature Post dates Post-term Prolonged . Definitions. Post term

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Post-term Pregnancy - Surveillance Strategies

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Post term pregnancy surveillance strategies

Post-term Pregnancy - Surveillance Strategies

Dr. Yasir Katib

MBBS, FRCSC, Perinatologist



  • Post mature

  • Post dates

  • Post-term

  • Prolonged



Post term

  • Refers to a pregnancy that has extended to or beyond a gestational age of 42.0 weeks or 294 days from the first day of the LMP

  • Postterm pregnancy is associated with increased perinatal mortality and morbidity




Depends upon the patient population

  • Percentage of primigravid women

  • Women with pregnancy complications

  • Ultrasound assessment of GA

  • Frequency of spontaneous preterm birth




  • In the United States, approximately 10% (range 3 to 14 percent) of all singleton pregnancies continue beyond 42 weeks of gestation

    WHO (1977), FIGO (1976)

  • 4% (2 to 7 percent) continue beyond 43 completed weeks in the absence of obstetric intervention

  • Definitions2


    • “Postdates” : the real issue is “post-what dates?”

    • “Post-term” or “prolonged” pregnancy are the preferred expressions for extended pregnancies



    • limited reliability with LMP to determine accurate post-term incidence

      • variations in timing of ovulation

      • irregular cycles

      • use of oral contraceptives

    • when early ultrasound dating used in conjunction to LMP, incidence of post-term decreased from 10 % (LMP alone) to 3% (LMP + U/S) (Reuss et. al 1995)



    • The etiology of abnormal prolongation of gestation is not well understood (theories)

    • Hypoplasia of the fetal adrenal gland with or without anencephaly

    • Placental sulfatase deficiency

    • Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency

    Morbidity and mortality

    Morbidity and Mortality

    • Increase mortality > 42 weeks gestation

    • evidence from studies done looking outcome of post-term pregnancies prior to availability of intervention methods

    Post term pregnancy surveillance strategies

    Perinatal mortality in late pregnancy according to gestational age in Sweden 1943-1952 compared with 1977-1978. Logarithm scale is used for convenience in depiction. (Adapted from Bakketeig and Bergsjø, 1991, and Lindell, 1956.)

    Post term pregnancy surveillance strategies


    40 WeeksPost-term

    (n = 8135)(n = 3457)

    Factor a (%) (%)

    Meconium 19 27

    Oxytocin induction 3 14

    Shoulder dystocia 8 18

    Cesarean delivery 0.7 1.3

    Macrosomia (> 4500 g) 0.8 2.8

    Meconium aspiration 0.6 1.6

    a For all comparisons between 40- and 42-week groups, P < 0.05.

    From Eden RD, Seifert LS, Winegar A, Spellacy WN. Perinatal characteristics of uncomplicated postdate pregnancies. Obstet Gynecol. 69:296, 1987.



    • Complications associated with fetal macrosomia include

    • prolonged labor

    • cephalopelvic disproportion

    • shoulder dystocia with resultant risks of orthopedic (eg, clavicular fractures) or neurologic injury (eg, brachial plexus palsy)

    Post term pregnancy surveillance strategies


    • Poor intrauterine growth are at increased risk

    • Umbilical cord compression from oligohydramnios

    • Nonreassuring fetal antepartum or intrapartum assessment

    • Cesarean delivery

    Dysmaturity syndrome

    Dysmaturity syndrome

    • Approximately 20%of postterm fetuses have a syndrome of fetal dysmaturity

    • long, thin, malnourished infant

    • Meconium staining

    • Peeling skin

    • Chronic intrauterine growth restriction from uteroplacental insufficiency

    Post term pregnancy surveillance strategies

    Postmature infant delivered at 43 weeks’ gestation. Thick, viscous meconium coated the desquamating skin. Note the long, thin appearance and wrinkling of the palms of the hands.

    Induction vs surveillance

    Induction vs. Surveillance

    • Several studies debate routine induction vs. surveillance

    • Hannah (1992)

      • Canadian trial showed routine induction reduced risk of perinatal death after 41 weeks, and not associated with increase risk of Caesarean section

      • cost analysis (Goeree 1995) showed induction less expensive than serial monitoring

    Induction vs surveillance1

    Induction vs.. Surveillance

    • NICH 1994

      • American study showed that active labour induction was not associated with improved outcome when compared to expectant management (at 41 weeks)

    • thus either induction or expectant management acceptable

    Induction vs surveillance2

    Induction vs.. Surveillance

    • No evidence to support elective induction or serial antenatal monitoring for uncomplicated pregnancy from 39-40 6/7 weeks

    Surveillance methods

    Surveillance Methods

    • Biochemical markers

      • Plasma or urine estrogen

      • Human Placental Lactogen

      • Placental proteins

         no evidence to demonstrate benefit as antenatal surveillance for fetal well being in post-term pregnancies

    Surveillance methods1

    Surveillance Methods

    • Non-invasive

      • Fetal movement counts

      • Non stress test (Cardiotocography)

      • Biophysical Profile

      • Amniotic Fluid Volume estimates

      • Doppler Ultrasound

    Surveillance methods2

    Surveillance Methods

    • Others

      • Oxytocin challenge test / Contraction stress test

      • Amniocentesis

        • Knox et al (1979)

          • meconium detected by amniocentesis associated with intrapartum fetal distress; however induction of labour did not improve outcome

    Surveillance methods3

    Surveillance Methods

    • NST

      • False-normal Non-stress Tests (Smith et al.1987)

        • fetal death within 7 days of normal non-stress tests

        • most common indication for testing was prolonged pregnancy

        • mean interval between test and death was 4 days, range of 1-7 days

        • single most common autopsy finding: meconium aspiration

        • investigators concluded that the non-stress test not adequate to preclude an acute asphyxial event

        • other biophysical characteristics might be beneficial adjuncts: For example, assessment of amniotic fluid volume

        • high false negative rates also reported by Miyazaki & Miyazaki (1981)

    Surveillance methods4

    Surveillance Methods

    • Ultrasound assessment of amniotic fluid

      • increased incidence of fetal compromise with oligohydramnios in post-term pregnancies

      • identification of decreased amniotic fluid may identify post-term fetus in jeopardy

    Surveillance methods5

    Surveillance Methods

    • Ultrasound Amniotic Fluid Estimates

      • qualitative (Crowley 1980)

        • presence of amniotic fluid between fetal trunk and limbs or uterine wall

      • quantitative

        • Largest single pocket method

        • Amniotic Fluid Index

    Amniotic fluid volume estimates

    Amniotic Fluid Volume Estimates

    • Largest Pocket measurements

      • usually measured in the vertical

      • in BPP, a score of 2 is given for the presence of a 2x2 amniotic fluid pocket

      • studies of AFV estimation have had different lower limits ranging from 1-3cm (Manning 1980, Chamberlain 1984,Crowley 1984, Phelan 1985, Bochner 1987)

    Amniotic fluid volume estimate

    Amniotic Fluid Volume Estimate

    • studies show that AFV may be effective discriminatory test in post-term pregnancy (Crowley 1984, Phelan 1985, Manning 1980)

    • normal AFV does not preclude absence of adverse outcome

    Amniotic fluid volume estimate1

    Amniotic Fluid Volume Estimate

    • Amniotic Fluid Index

      • first proposed by Phelan (1986) and Rutherford et al (1987)

      • summation of vertical pockets in four quadrants

      • table of gestational age-dependent norm of AFI (Moore 1990); e.g. after 41weeks lower limit is 67 mm.

    Amniotic fluid volume estimate2

    Amniotic Fluid Volume Estimate

    • AFV vs. AFI

      which is better???

    Doppler ultrasound

    Doppler ultrasound

    • Fetal application first reported by Fitzgerald and Drumm (1977)

    • non-invasive technique that uses high-frequency sound to investigate blood flow by detecting change in frequency of reflected sound

    Doppler ultrasound1

    Doppler Ultrasound

    • Theoretically, in post-term pregnancy:

      • increasing placental ‘age’ with increasing uteroplacental insufficiency

      • expect diminished uteroplacental flow, increased vascular resistance in umbilical artery and compensatory increased fetal cerebral artery flow (as in IUGR)

    Doppler ultrasound2

    Doppler Ultrasound

    • Several small studies have reported conflicting results

    • positive studies usually small (Devine et al 1994, Anteby et al, 1994) or have strict criteria which are not common e.g. Absent end diastolic flow (Pearce et al, 1991)

    Doppler ultrasound3

    Doppler Ultrasound

    • Negative studies show poor discrimination of potential fetal compromise (Guidetti 1987, Farmakides 1988)

    • Zimmerman et al (1995) showed that Doppler of uterine artery had a sensitivity of 7% in predicting poor outcome

    Doppler ultrasound4

    Doppler Ultrasound

    • Thompson and Trudinger 1990:

      • Observations using placenta and mathematical models

      • the larger the placenta (and its arterial branches), the greater fraction of vessels need to be obliterated before RI becomes abnormal

      • this may explain poor sensitivity of umbilical Doppler in post-term pregnancies

    Clinical practice guidelines

    Clinical Practice Guidelines

    • ACOG Practice Patterns (1997)

      • “Due to ethical and medico-legal concerns, it is highly unlikely that any subsequent studies will include a no-monitoring group”

      • “…antenatal surveillance has become a standard practice on the basis of universal acceptance”

    Clinical practice guidelines1

    Clinical Practice Guidelines

    • ACOG Practice Patterns (1997)

      • Antenatal surveillance should be initiated by 42 weeks of gestation (C:III)

      • No single antenatal surveillance protocol for monitoring fetal well-being in a post-term pregnancy appears superior to another

    Clinical practice guidelines2

    Clinical Practice Guidelines

    • SOGC Committee Opinion (1997)

      1. Establish gestational age

      2. For uncomplicated pregnancy, no evidence to support elective induction or commencement of serial antenatal monitoring at 39 to 40 6/7 weeks

    Clinical practice guidelines3

    Clinical Practice Guidelines

    • SOGC Committee Opinion (1997):

      3. Women who reach 41 to 42 weeks of gestation (uncomplicated pregnancies) should be offered elective delivery

      4. Serial fetal surveillance should consist (as a minimum) of an ultrasound assessment of amniotic fluid volume twice weekly…other forms of monitoring may be added to this (BPP, NST and fetal movement count)

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