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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