Case 83: Prolonged pregnancy

 CASE 83: PROLONGED PREGNANCY

History

A 27-year-old primigravid woman is seen in the antenatal clinic at 41 weeks 2 days’ gestation.

This pregnancy was conceived naturally and 12-week ultrasound scan confirmed the estimated due

date. All routine investigations and monitoring during the pregnancy have been unremarkable.

She reports the baby moving regularly (more than 10 times per day) and apart from Braxton

Hicks contractions, she has had no signs of labour.

Examination

The blood pressure is 116/64 mmHg. The urinalysis shows no proteinuria.

The symphysiofundal height is 39 cm. Presentation is cephalic with 2/5 of the head palpable.

The fetal heart is auscultated at 148/min and an acceleration is heard during auscultation.

Questions

• How will you counsel this woman about the potential advantages and disadvantages

of induction of labour?

• Assuming the decision is made to proceed with induction of labour, outline the process.100 Cases in Obstetrics and Gynaecology

234

ANSWER 83

Prolonged pregnancy, defined as pregnancy continuing beyond 42 weeks’ gestation, occurs

in 5–10 per cent of women. Prolonged pregnancy is associated with an increased risk of stillbirth, though the absolute risk of this remains low (2–3/1000). Induction of labour for prolonged pregnancy (‘post dates’) is recommended between 41 and 42 weeks’ gestation.

Advantages

Reduced risk of stillbirth associated with prolonged pregnancy – the relative risk of stillbirth

from induction of labour after 41 weeks (versus expectant management) is 0.30.

Some women express the wish to deliver soon after 40 weeks because of discomfort, anxiety

or social reasons.

Disadvantages

• Uterine hyperstimulation (1–5 per cent).

• Failed induction (15 per cent) – may require repeat induction process or caesarean section.

• Induction of labour can be a prolonged process – sometimes taking more than 24 h

for labour to be established.

• Approximately 500 women need to undergo induction of labour to prevent one

baby death.

• There is some evidence that induced labour is associated with greater analgesia

requirement than spontaneous labour.

Process of induction of labour

Membrane sweep

Membrane sweep after 41 weeks’ gestation reduces the need for induction of labour (relative

risk 0.59), with eight women needing to undergo membrane sweep to prevent one formal

induction of labour. Membrane sweeping can be repeated and probably works by causing

local release of prostaglandin.

Prostaglandin

Vaginal prostaglandin E2 (PGE2) is the usual agent used for induction of labour. Typically a

slow-release PGE2 tablet/gel is used, or a controlled-release pessary, which has the advantage

of being removable if hyperstimulation occurs.

The decision to give prostaglandin or perform amniotomy is based on the modified Bishop

score (see Table 83.1). The Bishop score should then be reassessed 6 h after vaginal PGE2 insertion, or 24 h after vaginal PGE2 controlled-release pessary insertion, to monitor progress.

Mechanical dilatation of the cervix

Some mechanical (non-pharmacological) methods are available to cause cervical dilatation

but are not in routine practice.

Amniotomy

Artificial rupture of the membranes is performed once the Bishop score is 6 or more. In

some women, particularly multigravida women, it may be possible to perform amniotomy at

presentation, thus preventing the need for prostaglandins. Most women however will need at

least one dose of prostaglandin prior to amniotomy.Case 83: Prolonged pregnancy

235

Oxytocin

Intravenous oxytocin infusion should be started after amniotomy. The dose is titrated against

the fetal heart rate and contractions, with the aim of achieving three or four contractions

every 10 min.

Fetal monitoring during induction of labour

Electronic fetal monitoring (EFM) should be carried out before and after either insertion of

prostaglandin or amniotomy. Following this, intermittent auscultation is reasonable until

either labour is established or oxytocin is commenced, from which point continuous EFM

is required.

Expectant management of prolonged pregnancy

In a woman who declines induction of labour for prolonged pregnancy beyond 42 weeks’ gestation, increased antenatal monitoring consisting of at least twice-weekly cardiotocography

and ultrasound estimation of maximum amniotic pool depth should be offered.

KEY POINTS

• Induction of labour is recommended between 41 and 42 weeks’ gestation to

reduce the risk of stillbirth.

• The relative risk of stillbirth is 0.3 for induction of labour after 41 weeks (versus

expectant management).

• Prostaglandin gel or pessary is the most common induction agent, but induction

may also be achieved by membrane sweep or amniotomy alone.