Post-Date and post-term Pregnancies
*Postterm pregnancy includes pregnancies that last longer than 42 weeks.
*Postdate pregnancies last longer than the established or estimated date of
confinement (ie, 40 wk).
The reported frequency of postterm pregnancy is approximately 3-12%.
Assuming that the incidence of postdate pregnancy may be slightly higher
than that of postterm pregnancy is reasonable.
Unknown, but hereditary, hormonal and non-engagement of the presenting part are suspected factors.
An obvious cause of both postterm and postdate pregnancy is inaccurate dating criteria.
Ultrasound dating can be inaccurate for a patient who presents late in pregnancy and is unsure of her last menstrual period (LMP).
When using ultrasound criteria for the dating of a pregnancy, it is necessary to understand the margin of error reported at various times during each trimester.
A calculated gestational age by composite biometry from an ultrasound must be considered an estimate and must take into account the range of possibilities.
*crown-rump length (CRL) is 3-5 days,
* ultrasound performed at 12-20 weeks of gestation is 1 week,
*at 20-30 weeks is 2 weeks, and
*after 30 weeks is 3 weeks. Thus, a pregnancy that is 35 weeks by ultrasound could actually be anywhere from 32 weeks to 38 weeks (35 wk +/- 3 wk).
A way to more accurately date a pregnancy when composite biometry is not consistent in all of the parameters (ie, biparietal diameter [BPD], head circumference, abdominal circumference, femur length), is to evaluate the transcerebellar diameter. The diameter in millimeters corresponds to weeks of gestation up to 24 weeks; thereafter, charts are available to calculate gestational age.
If the transcerebellar diameter cannot be obtained, the
criterion standard for dating in the second trimester is the BPD.
Risk of Post-term
1. Placental insufficiency : which may lead to growth restriction, fetal hypoxia or even death.
2. Oligohydramnios: with its sequelae particularly cord compression during labor.
3. Obstructed labor: due to
- Oversized baby,. The risk for macrosomia, shoulder dystocia and cephalopelvic disproportion increase in postterm pregnancy
- no moulding of the skull due to more calcification.
4- Increased incidence of operative delivery.
5-The risk for perinatal mortality increases in the postterm pregnancy
NB. Perinatal morbidity and mortality do not increase appreciably between 40-41 weeks of gestation; however, several complications are associated with longer gestations
To deliver or not:
W hen determining a management plan for postdate pregnancy (>40 wk of gestation but <42 wk),
*the first decision is whether to deliver a patient and, if so,
* when and by what route.
The first decision that must be made when managing a postdate pregnancy is whether to deliver.
In certain cases (eg, nonreassuring surveillance, oligohydramnios, growth restriction, certain maternal diseases), the decision is straightforward. In these high-risk situations, the time at which the risks of remaining pregnant begin to outweigh the risks of delivery may come at an earlier gestational age.
NB If pregnancy is at risk for an adverse outcome from an underlying condition, either maternal or fetal, inducing labor may proceed without documented lung maturity.
Also, an elective induction of labor may proceed at or after 39 weeks of gestation in the absence of documented lung maturity provided that:
1-36 weeks have elapsed since documentation of a positive human chorionic gonadotropin (+hCG) test finding,
2- 20 weeks of fetal heart tones have been established by a fetoscope or
3- 30 weeks by a Doppler examination, or
4- 39 weeks’ gestation have been established by a CRL or
5- by an ultrasound performed before 20 weeks of gestation consistent with dates by the patient's Last Menstrual Period.
There are frequently several options to consider when determining a course of action in the low-risk pregnancy.
1-The certainty of gestational age,
2-cervical examination findings,
3-estimated fetal weight,
4-and past obstetrical history
These factors must all be considered when mapping a course of action.
Involving the patient in this discussion is wise because her feelings and understanding of the situation are important as well.
*pregnancy should not be allowed to progress beyond 42 weeks of gestation.
*The question of how a pregnancy between 41-42 weeks should be managed remains.
-the main argument against a policy of routine induction of labor at 41-42 weeks is that induction increases the rate of cesarean delivery without decreasing maternal and/ or neonatal morbidity
- A recent review in the Cochrane Library concluded that routine induction in low-risk pregnancies at or after 41 weeks’ gestation is associated with a reduction in perinatal mortality, with no increase in the rate of instrument deliveries or cesarean delivery.
If the physician decides not to deliver.... the decision whether to institute antepartum fetal surveillance and what method(s) of surveillance to use must be discussed with the patient.
Antepartum fetal surveillance should be used in postterm pregnancies (ie, >42 wk of gestation) when delivery is not performed (usually for obstetrical contraindications).
Evidence to suggest that antepartum surveillance improves outcomes before 41 weeks’ gestation in low-risk pregnancies is insufficient, and routine use of antepartum surveillance between 40-41 weeks’ gestation is not supported by the literature.
* An amniotic fluid index of more than 8 cm and a reactive fetal heart rate tracing are reassuring.
-When performing the fetal heart rate tracing, the patient may be seated or in a lateral recumbent position with lateral tilt.
-Two accelerations in the fetal heart rate of 15 beats per minute over baseline in a 20-minute period constitute a reactive tracing.
-If the tracing is not reactive within the first 20 minutes, the test may be extended another 20 minutes.
-If the tracing remains nonreactive, a backup test must be performed in order to be sure that the intrauterine environment is still safe.
-A contraction stress test or
- A full biophysical profile
are both acceptable backup tests.
These may also be used if the tracing is reactive but shows fetal heart rate decelerations.
However, in the pregnancy that is beyond 41 weeks of gestation, the threshold for delivery should be very low.
*Twice-weekly testing of patients at risk for fetal distress was superior to weekly testing,
* A modified biophysical profile consisting of a nonstress test and an amniotic fluid index have been shown to be as sensitive as a full biophysical profile.
Induction of Labor and Intrapartum Management
When the decision to deliver a patient has been made, the route of delivery and the specifics of intrapartum management depend on individual circumstances.
About 80% of patients who reach 42 weeks’ gestation have an unfavorable cervical examination finding (ie, Bishop score <7)
Prostaglandin E2 gel and suppositories for vaginal application were used extensively until the late 1990s, when many pharmacies stopped manufacturing them because of the advent of commercially available and less labor-intensive preparations.
Currently available chemical preparations include prostaglandin E1 tablets for oral or vaginal use, prostaglandin E2 gel for intracervical application, and a vaginal insert containing 10 mg of dinoprostone.
The progesterone antagonist RU486 may become available, but it has been studied less than other pharmacologic agents.
These devices may act by a combination of mechanical forces and by causing release of endogenous prostaglandins.
*Membrane sweeping or stripping
* Foley balloon catheters placed in the cervix
* Extra-amniotic saline infusions, and laminaria
All have all been studied and have been shown to be effective .
NB- Be aware of the potential hazards surrounding the use of
these agents in the patient with a scarred uterus.
-The potential for uterine tachysystole and subsequent fetal distress requires
that care be taken to avoid using too high a dose or too short a dosing
interval in an attempt to get a patient delivered rapidly.
-Care should also be taken when using combinations of mechanical and pharmacologic
methods of cervical ripening.
-It is necessary to watch for the major potential complications associated with inductions beyond 41 weeks’
gestation and to have a plan for dealing with each.
*the presence of meconium,
*fetal intolerance to labor.
The farther pregnancy progresses beyond 40 weeks, the more likely it is that significant amounts of meconium will be present. This is due to
-increased uteroplacental insufficiency, which leads to hypoxia in labor
and activation of the vagal system
-the presence of less amniotic fluid increases the relative amount of meconium in utero.
To counter the effects of meconium, a combination of amnioinfusion of isotonic sodium chloride solution and prompt suctioning of the oropharynx and nose upon delivery of the head must be considered.
Fetal macrosomia can lead to maternal and fetal birth trauma and to arrest of both first- and second-stage labor.
-Estimated fetal weight should be documented prior to beginning a postdate induction.
-Mid-pelvic instrument deliveries should not be attempted.
-The most important part of a delivery plan is being prepared for shoulder dystocia
in the event that this unpredictable, anxiety-provoking, and potentially
dangerous condition arises.
Fetal Intolerance to labor
Intrapartum fetal surveillance in an attempt to document fetal intolerance to labor before it leads to acidosis is critical.
Whether continuous fetal monitoring or intermittent auscultation is used, interpretation of the results by a well-trained clinician is of paramount importance.
If the fetal heart rate tracing is equivocal, fetal scalp stimulation, fetal scalp blood sampling, and/or fetal pulse oximetry may provide the reassurance necessary to justify continuing the induction of labor.
If no reassurance that the fetus is tolerating labor, cesarean delivery is recommended.