POSTTERM PREGNANCY
AZZA ALYAMANI
OBSTETRICS & GYNICOLOGY
Department
King Khalid University
Introduction
Post term pregnancy is a common situation. It
cause anxiety for both women and obstetricians
because it perceived as being a cause of increased
risk to the fetus.
Post term pregnancy per se is not a pathological
condition and should not be confused with the
post maturity syndrome described by Clifford in
1954.
Definitions
* Post term ( prolonged pregnancy ) :
it is 42 completed weeks or more ( 294 days).
this definition is accepted by both WHO & FIGO.
* Post maturity syndrome :
it is IUGR with associations of ,meconium
stained amniotic fluid , oligohydramnios , fetal
distress , loss of subcutaneous fat and dry
cracked skin reflecting placental insufficiency.
* Past date :
past the calculated EDD before 42 weeks.
Incidence :
5 -10 %
Dating by the last menstrual period (LMP) alone ,
has a tendency to overestimate the GA .
While the use of early ultrasound alone , to calculate
GA , significantly reduced the incidence of post term
pregnancy . Ia
Importance
A) Fetal and Neonatal risks
* It is likely that the majority of morbidity
and mortality associated with post term
pregnancy, arises because of post maturity.
* Post term pregnancies are associated
with excess perinatal morbidity & mortality .
* Delivery at 42 week is associated with a
doubling of the perinatal mortality rate , unlike
the 37 -41 week period in which antepartum
deaths contribute about 2/3 of the total .
When lethal congenital abnormalities are
excluded ,intrapartum fetal death is 4 times more
common,
and
neonatal death is 3 times more common
in infant s born after 42 weeks.
In addition , meconium staining of the amniotic
fluid and the likely of intrapartum fetal hypoxia
were much more common in post term
pregnancies compared to those delivered at 40 ws.
This result in fetal acidosis , neonatal seizures &
perinatal death . Post term pregnancy is also a
risk factor for birth trauma and shoulder dystocia.
B) Maternal risks of post term pregnancies:
* increased operative delivery , hemorrhage and
maternal infection.
* in addition , psychological morbidity as
increased maternal anxiety .
Etiology
Not Clear
It is common in :
* primigravida
* previous post term pregnancy. 30%
The cause may be due to :
1. low cortisol levels with post term fetal distress.
2. relative adrenocortical insufficiency leading to
delay in the onset of labor & increased risk of
intrapartum hypoxia or death.
Support for this theory is that :
infants delivered following a post term pregnancies
are at increased risk of :
* sudden infant death syndrome.
* death up to 2 years of age.
Fetal Assessment
Monitoring Post term Pregnancy
The perinatal mortality does not significantly rise
until 42 ws. gestation ,thus there is no need to offer
fetal monitoring prior to this gestation, if it is not
offered at term .
There is no consensus about the appropriate
surveillance to post term pregnancy and no clear
evidence exists to support that fetal monitoring
can reduce the perinatal mortality.
* simple fetal monitoring is as effective as more
sophisticated monitoring of post term pregnancies
* The use of Doppler analysis of various arterial
systems as uterine , umbilical ,middle cerebral
and descending aorta in uncomplicated post term
pregnancies is not different from that in term
pregnancies.
Therefore
the recommended fetal monitoring
in post term pregnancy
is
a) Amniotic fluid measurement
Liquor volume fall after term , thus AFI does
not improve perinatal outcomes , thus the mean
pool depth (MPD) is the tool of choice for monitoring
liquor in post term pregnancy. Ib
b) CTG
Simple monitoring with NST and liquor
assessment holds an advantage over the formal
biophysical profile scoring.
It is therefore ,vital that each woman is treated
on an individual basis and counseled regarding
the risks of post term pregnancy.
Management
(1) induction of labor at 41+ weeks
to reduce perinatal mortality , meconium staining
of the amniotic fluid and small decrease in
caesarean section rate . 1a
(2) conservative management
with close fetal surveillance, this can reduce
excess operative delivery in women who will
opt to for conservative management .
Other interventions:
a. nipple stimulation
but have not been shown to be of benefit .
b. sweeping the membranes
at or beyond 40 weeks appear to significantly
reduce the incidence of post term pregnancy
and should be offered to all women.
Key points:
1. the use of early ultrasound dating , reduces the
incidence of postterm pregnancy.
2. induction of labor after 41+ weeks reduces perinatal
mortality rates without increasing CS rates.
3. sweeping the membranes significantly reduces the
incidence of postterm pregnancy .
4. no clear evidence that fetal monitoring can reduce the
perinatal mortality in postterm pregnancy.
5. the use of NST and liquor assessment in monitoring
postterm pregnancy twice weekly is recommended in
women who prefer conservative management with
fetal surveillance.
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