prolonged pregnancy

Prolonged pregnancy
Prolonged pregnancy is defined as pregnancy which progresses
beyond 42 weeks.
[
1
]
Prolonged pregnancy is associated with fetal,
neonatal and
maternal complications. Risks increase after term
and significantly so after 41 weeks of pregnancy. A policy of
induction of labour appears to improve outcomes and reduce
perinatal mortality.
[
2
]
Where possible, first trimester ultrasound
rather than last menstrual period (LMP) dating should be relied
on to assess pregnancy duration. This should be determined
using crown
-
rump measurement or head circumference if cro
wn
-
rump length is above 84 m
Risks associated with post
-
term
pregnancy
[
4
]
Fetal and neonatal risks
Prolonged pregnancy is associated with an increase in
perinatal
morbidity and mortality. There is an increased risk of stillbirth and
neonatal death, as well as an increase in risk of death in the first year
of life. The increased mortality is thought to be due to factors such as
utero
-
placental insufficiency
, meconium aspiration and intrauterine
infection.
Fetal morbidity is also increased, with higher risks of:
?
Meconium aspiration.
?
Macrosomia and larger babies resulting in:
?
Prolonged labour.
?
Cephalo
-
pelvic disproportion.
?
Shoulder dystocia.
?
Birth injury resul
ting in, for example, brachial plexus damage or
cerebral palsy.
?
Neonatal acidaemia.
?
Low five
-
minute Apgar scores.
?
Neonatal encephalopathy.
?
Neonatal seizures.
?
Features of intrauterine growth restriction (IUGR) due to placental
insufficiency
Maternal risks
Prolonged pregnancy is also associated with increased risk for the
mother, including:
?
Obstructed labour
?
Perineal damage
?
Instrumental vaginal delivery
?
Caesarean section
?
Postpartum haemorrhage
?
Infection
Where labour is induced before the uterus or cervix are
in a
favourable state, obstetric problems may follow which can have an
adverse effect on either mother or baby, including:
?
Need for caesarean section.
?
Prolonged labour.
?
Postpartum haemorrhage.
?
Traumatic delivery.
Epidemiology
?
The use of ultrasound in earl
y pregnancy for precise dating is
thought to reduce the number of post
-
term pregnancies compared to
dating based on the LMP.
[
5
]
?
5
-
10% of pregnancies are
prolonged beyond 42 weeks.
[
1
]
?
Around 20% of pregnant women will need induction of labour
-
the
majority for post
-
term pregnancy.
[
6
]
Risk factors
[
4
]
?
Previous post
-
term pregnancy increases the risk of recurrence in
subsequent
pregnancies.
?
Primigravidity.
?
High maternal BMI is associated with longer gestation and increased
rate of induction of labour.
[
7
]
Elevated pre
-
pregnancy weight and
maternal weight gain both increase the risk of a post
-
term delivery.
[
8
]
?
Genetic factors. There is an increased risk of post
-
term pregnancy
for mothers who were
themselves born post
-
term and twin studies
also suggest a genetic role.
?
Advanced maternal age.
[
9
]
Presentation
Symptoms
?
When post
-
term, the neonate has lower tha
n normal amounts of
subcutaneous fat and reduced mass of soft tissue.
?
The skin may be loose, flaky and dry.
?
Fingernails and toenails may be longer than usual and stained
yellow from meconium.
Signs
?
Before delivery there may be reduced fetal movement.
?
A
reduced volume of amniotic fluid may cause a reduction in the
size of the uterus.
?
Meconium
-
stained amniotic fluid may be seen when the membranes
have ruptured..
Management
Increasing evidence shows that a policy of induction of labour is
associated with
fewer perinatal deaths and fewer caesarean sections
when compared to expectant management.
[
2
]
The Royal College of
Obstetricians and Gynaecologists (RCOG)/Nationa
l Institute for Health
and Care Excellence (NICE) guidelines recommend that women
should be offered induction after 41 weeks between 41+0 and 42+0
weeks to avoid the risks of post
-
term pregnancy, primarily increased
intrauterine fetal death
.
[
1
]
Prior to formal induction of labour, women
should be offered vaginal examination with membrane sweeping.
[
3
]
If
women choose not to have induction, this decision should be
respected and from 42 weeks of pregnancy there should be increased
monitoring with at least twice
-
weekly cardiotocography and ultrasound
estimation of maximum amnio
tic pool depth.
Studies have also looked at the outcomes when labour is induced
between 37 and 41 weeks of pregnancy and it appears to also reduce
perinatal mortality without increasing risk o