Max Brinsmead MB BS PhDMay 2015
Definition and Incidence
Prolonged pregnancy is defined as that proceeding beyond 42 weeks gestation
In the absence of any medical intervention, the incidence has been described as between 5% and 10% of women with singleton pregnancies
The Problem Epidemiological studies demonstrate
that perinatal mortality rises beyond 41w○ Doubles at 42 weeks and○ Triples at 43 weeks but...
This is from a very low baseline so the absolute risk is small
○ Approx. 3 per thousand but...
There are racial and ethnic differences○ Lowest in whites○ Higher in blacks○ Highest is southern Asians in a UK study
Increased Perinatal Mortality may be due to…
“Ageing” of the placenta Increasing rates of meconium and
meconium aspiration○ This occurs with intrauterine asphyxia
Increasing size of the fetus... Although most studies point to relative
IUGR as a risk factor post term And increased rates of CS after 42w are
for fetal distress rather than CPD or failure to progress
Induction of Labour (IOL) Carries risks such as...
○ Uterine hyperstimulation from oxytocic agents○ Chorioamnionitis from amniotomy○ Cord prolapse & fetal bleeding from vasa
previa (rare)○ The “intervention cascade”○ Failed induction of labour
It requires induction of labour in some 470 women to prevent one perinatal death
What is the Evidence? Metanalysis of 19 RCT’s with 7984
women concludes that IOL at 41 – 42 weeks compared to conservative management results in lower PNM
RR 0.30, CI 0.09 – 0.99 But there are many problems with all of
the trials e.g.○ Protocol violations○ They are unblinded○ May not be relevant for all populations
Perinatal deaths in the control group…
Meconium aspiration (4) Intrauterine death (2)
But one occurred in a mother with gestational diabetes
Neonatal pneumonia (1)GBS screening presumably not done
There were no deaths in the IOL group
Safe conservative management is possible
In a RCT of 508 women in Sweden 254 subject to IOL at 41w & 2d 254 monitored by CTG and AFI every 3rd
day to 43w There was no difference in:
○ Rate of Caesarean birth○ Rate of assisted vaginal birth○ Severe perineal injury or PPH○ Meconium liquor○ 5-minute Apgar○ Admission to NICU○ Perinatal death (one only in controls due to
true knot in the cord)
From a practical point of view
A policy of routine induction of labour is only applicable if dates are known with accuracy
This requires routine ultrasound to confirm dates at <16 weeks gestation
○ NICE guidelines
It is best practice to discuss the pros and cons of IOL with women & to involve them in the decision process
When dates are certain then NICE guidelines
recommend… That information about prolonged
pregnancy is provided to all women and specifically at 38+w.
At 40 - 41w nulliparous women be offered vaginal examination (VE) with membrane sweeping
At 41w parous women be offered VE with membrane sweeping
That all women with uncomplicated pregnancies be offered induction of labour at 41 – 42w
Membrane Sweeping A systematic review of 22 RCT’s with
2797 women shows that sweeping the membranes...
○ Reduces the number of pregnancies >41 w RR 0.59, CI 0.46 – 0.74
○ Saves one induction of labour for every 8 performed
○ Has no effect on the rate of CS○ Has no increased risk of maternal or neonatal
infection○ Causes some pain in most women○ Causes uncomplicated bleeding in a few women○ Is more successful in parous women than
nulliparas
Membrane Sweeping (2)
Unanswered questions include...○ When it should be commenced○ How often○ What can be done if the cervix is closed○ Sweeping in the vaginal fornix is
recommended
If a patient declines induction of labour past term NICE guidelines
recommend…
That patients be offered increased surveillance and nothing less than...
○ Twice weekly CTG○ An ultrasound estimate of amniotic fluid
volume
There may be advantages in continuing VE’s and sweeping of membranes
When dates are uncertain then it is appropriate…
That an assessment is made at each visit of the possible risks associated with prolonged pregnancy and the risks associated with induction of labour
This includes the possible risk of delivering a premature infant in error
The assessment may or may not include VE and sweeping of membranes
Concern when monitoring a fetus at risk from prolonged pregnancy MAY
include… Maternal conditions known to be associated with a
risk of intrauterine death e.g.○ Gestational diabetes○ Hypertension in pregnancy○ Smoking○ Recurrent APH○ Malaria and severe anaemia etc.
Past obstetric history of...○ Stillbirth or neonatal death○ Meconium-complicated pregnancies○ IUGR
Oligohydramnios Decreasing fetal movements Failure of maternal weight gain Static symphysis-fundal height
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