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INTRODUCTION
There is a continuing controversy
regarding the management of the pregnant patient who has not delivered
by her "due date". Induction of the undelivered post-term
patient, rather than allowing spontaneous labor, places the patient at
higher risk for failed induction, cesarean delivery, and its attendant
complications. This issue of Clinical Discussions addresses the
management of the "postdates" patient.
Definition
Postdates is traditionally defined as completing 42 weeks of gestation,
or 294 days of pregnancy beyond the LMP (last menstrual period). Post
term is also occasionally used to describe postdatism. The term
"post maturity" is used to describe the features of a neonate
who appears to have been in-utero longer than 42 weeks of gestation.
These features were originally described by Clifford (1954) and consist
of 3 stages:
- 1 - wrinkled, peeling skin, with
thin body
- 2 - stage 1 and fetal distress,
meconium present
- 3 - stage 1 & 2, findings with
meconium stained skin or nails
The Clifford criteria has been more
recently modified to describe dysmaturity, which is defined as mild
-only skin and nail findings, or advanced -skin, nail findings
and loss of subcutaneous fat with meconium staining.
Dysmaturity is seen in 20 - 43% of
postdates pregnancies. At 41 - 43 weeks of pregnancy the prevalence of
dysmaturity is 2 - 3%, and at 44 - 45 weeks of pregnancy dysmaturity
prevalence is as high as 75%.
The incidence of postdates ranges from
3 - 12% of all pregnancies. If the pregnancy is dated using ultrasound
criteria, the incidence of post-dates is lower and ranges from 3 - 6%.
Only 1 - 4% of all pregnancies continue to 43 weeks.
Management
What is not controversial regarding the management of the postdates
patient is:
- Do not allow any pregnancy with
other high risk factors to go postdates - perinatal morbidity is too
high. the rate is twice as high in the high-risk patient as the
low-risk patient. Eden (1988) found the morbidity rate five times
higher in the hypertensive and diabetic patient than the
uncomplicated low-risk patient.
- If the post-term patient has a
favorable cervix (Bishop's score > 6, then induction of
labor is the preferred management.
What is controversial is what
to do with postdates pregnancy with an unfavorable cervix: to induce or
not to induce labor? Grenados (1984) surveyed 80 perinatal centers and
found that 49% would managed the patient conservatively if fetal
distress was not present and 49% would induce labor or perform a
cesarean section.
To answer the question of whether to
induce, the risk of prolonging the pregnancy (conservative management)
must be weighed against the risk of labor induction (active management).
To determine whether a patient is a candidate for conservative
management, it is crucial to determine whether the fetus is at risk,
what test of fetal surveillance is best, when should testing begin, and
how often should testing be performed.
Fetal Surveillance
Fetal risks (mortality and morbidity) of prolonged pregnancy has been
significantly reduced after the availability of antenatal testing.
McClure (1958) in England studied 17,000 deliveries and found the
perinatal mortality rate ranged from 10/1000 at 40 weeks gestation to
17/1000 at 42 weeks gestation on up to 50/1000 at 45 weeks gestation.
With the advent of antenatal testing which became available in the late
1970's, Eden (1987) demonstrated a significant decrease in the perinatal
mortality rate; at 40 weeks gestation - 1.5/1000, 43 weeks gestation -
2.0 /1000, and at 44 weeks gestation - 6.9/1000.
There is morbidity's associated with
conservative managment of postdates pregnancy. The fetus is at risk for
meconium staining of amniotic fluid (15 - 20%), meconium fluid in the
trachea/larynx, which requires aggressive airway management, and
meconium aspiration syndrome, which has a very high mortality rate.
Other complications include oligohydramnios, dysmaturity and macrosomia
(prevalence of 2 -10%). Older studies suggested that postdates
pregnancies accounted for a high proportion of infants with cerebral
palsy, and children with learning disabilities. Fortunately more recent
studies (Shime, 1988) do not support this concept except in pregnancies
complicated by asphyxia or meconium aspiration syndrome.
There are several fetal surveillance
test available which can reduce the morbidity and mortality associated
with the postdates pregnancy. Briefly they are:
Nonstress Test (NST)
- reactive - 2 accelerations (15 beats
above baseline lasting 15 seconds) in 20 minutes
- nonreactive - after 40 minutes no
accelerations
Contraction stress test (CST)
- IV oxytocin or nipple stimulation
until patient has 3 contractions in 10 minutes negative - no
decelerations positive - repetitive late decelerations or variable
decelerations suspicious - isolated late or variable decelerations
Biophysical profile (BPP)
- reactive NST, fetal breathing,
extension - flexion, gross body movement, 2 cm X 2 cm pocket; 2
points for the presence of each variable
Doppler
- multiple studies assessing almost
any vessel (Arduini, 1991, Pearce, 1991, Johnstone, 1993) suggest
that Doppler is not helpful even using absent end diastolic flow.
ACOG continues to consider Doppler investigational
Fetal "Kick Counts"
- various protocols are described, and
well controlled studies support its use.
What's the best test and when
should testing begin?
Although Eden's (1982) study is greater than 15 years old it is one of
the few which looked at the issue of which surveillance scheme is best
for reducing perinatal mortality and morbidity. The study compared 3
testing schemes using 583 postdates patients. He compared: a. weekly NST/CST,
b. semiweekly NST/BPP, and c. semiweekly NST/weekly amniotic fluid
volume (AFV) assessment.
The lowest perinatal mortality
and morbidity was seen in the scheme in which semiweekly NST/weekly AFV
were performed. However the intervention rate was the highest
in this group. This implies that a higher intervention rate is
acceptable to obtain a low PNM. Other studies (Freeman, 1981) have
demonstrated similarly low perinatal morbidity and mortality rates using
the CST semiweekly.
Regarding the issue of "when to
begin testing" several studies have compared initiating fetal
surveillance at 40, 41. or 42 weeks of gestation. The results reveal the
same morbidity (oligohydramnios, cesarean section for fetal distress,
NICU admission) in patients with testing initiated at 41 or 42 weeks.
Therefore if testing is begun too early (i.e 40 or 41 weeks gestation) a
patient may receive 3 - 4 additional tests without reducing the risk to
the fetus. If testing is delayed until 42 weeks, many patients will have
already presented in spontaneous labor. By 43 weeks gestation, 70 - 90%
of postdates patients will have already labored and delivered.
Induction vs. Surveillance
An evaluation of randomized prospective clinical trials give answers to
important questions regarding the safety of surveillance for the fetus
specifically addressing the issue of meconium staining, meconium
aspiration syndrome, dysmaturity, macrosomia and length of hospital stay
for the infant. Additionally assessment of the safety of induction for
the mother regarding issue of cesarean section rate, infectious
morbidity, and length of hospital stay becomes equally important.
Five randomized trials have addressed
this issue:
- Cardozo et al. 1986 (England) 402
patients. good dates, fluid check, NST every other day. induction -
PGE2 3mg pessary, AROM, +/- oxytocin, no limit on maximum
gestational age
- Augensen et al. 1987 (California)
214 patients, all nulliparous, Bishop same, NST q 3 -4 day, induced
by 43 weeks, induction - oxytocin, AROM, induced at 43 2/7 weeks
- Dyson et al 1987 (California) 302
patients, NST semiweekly, fluid check q weekly until 42 weeks then
semiweekly, induction - PGE2 gel intravaginal (3mg) or intracervical
(0.5mg), no limit on maximum gestational age
- NIH collaborative, 1991 (5 US
centers) 349 patients, NST, fluid check semiweekly, induction with
PGE2 (0.5mg) intracervical gel 1 dose only, +/- oxytocin, induced at
44 weeks
- Hannah et a 1992 (Canadian
multicenter trial) 3407 patients, NST 3 times per week, AFV check
2-3 X/week, induction within 4 days of randomization, induction with
gel in induction group, induction by oxytocin in surveillance group
The conclusion drawn from the
evaluation of a total of 4869 patients suggest that there is no
difference in the mortality or morbidity between routine induction and
conservative managment of the postdates patient. In the Hannah study the
cesarean section rate was significantly higher in the surveillance group
vs. induction group (24% vs. 21%). The NIH study was discontinued
because morbidity and mortality was so low. The cost of either clinical
pathway has yet to be evaluated.
Recommendations for management
of the postdates pregnancy
- At 41.5 weeks begin antenatal
testing (NST and amniotic fluid index - AFI), cervical exam
- If any testing is abnormal (AFI <
= 5.0 cm, NST with any decelerations) induce
- If cervix is favorable (can rupture
membranes or Bishops >= 6) induce
- If macrosomia is suspected with EFW >=
4500 grams either induce or obtain ultrasound to confirm and induce
- Remaining patients are followed
semiweekly with NST, fluid check, and cervical exam and if any of
the above occur the patient is induced
- If not in labor by 43 weeks induce
- All patients are given kick count
instructions to perform daily.
Bibliography
- Augensen K, Bergsjo P, Eikeland
T, Askvik K, Carlsen J: Randomized comparison of early versus late
induction of labour in post-term pregnancy. Brit Med J 1987;294:
1192
- Cardozo L, Fysh J, Pearce JM:
Prolonged pregnancy: The management debate. Brit Med J 1986;293:1059
- Clifford SH: Postmaturity and
placental dysfunction. J Peds 1954;44:1
- Dyson DC, Miller PD, Armstrong
MA: Management of prolonged pregnancy: induction of labor versus
antepartum fetal testing. Am J Obstet Gynecol 1987;156:928
- Eden RD, Gergely RZ, Schifrin BS,
Wade ME: Comparison of antepartum testing schemes for the management
of the postdate pregnancy. Am J Obstet Gynecol 1982;144:683
- Eden RD, Seifert LS, Winegar A,
Spellacy WN,: Maternal risk status and postdate pregnancy:
Utilization of contraction stress testing for primary fetal
surveillance. Am J Obstet Gynecol 1981;140:128
- Granados JL: Survey of the
management of postterm pregnancy. Obstet Gynecol 1984;63:651
- Hannah ME. et al.: Induction of
labor as compared with serial antenatal monitoring in post-term
pregnancy. N Engl J Med 1992;326:1587
- Johnstone FD, et al.:The effect
of introduction of umbilical Doppler recordings to obstetric
practice. Br J Obstet Gynaecol 1993;100:733
- Pearce JM, McParland PJ: A
comparison of Doppler flow velocity waveforms, amniotic fluid
columns, and the nonstress test as a means of monitoring post-dates
pregnancies. Obstet Gynecol 1991;77:204
- Shime J, Gare DJ, Andrews, J,
Betrand M, Salgado J, Williams G: Prolonged pregnancy: Surveillance
of the fetus and the neonate and the course of labor and delivery.
Am J Obstet Gynecol 1984;148:547
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