Gerald Hurowitz, M.D.·Published 20 December 2008·7 min read
Key points
Preinsertion of multiple osmotic dilators 6 to 24 hours prior to amnio-infusion may reduce the time from induction to completion, reduce the risk of cervical laceration, and almost eliminate posterior wall rupture.
The optimal site for amniocentesis is approximately 2.5 cm below the most prominent part of the uterus as palpated through the abdominal wall.
Intra-amniotic installation of PGF2α is an effective technique but may be associated with the need for a second injection, transient fetal survival, failure, and significant GI side effects.
Intra-amniotic hyperosmolar urea (80 - 90 gms/100 mL 5% dextrose in water for a 59.7% concentration) is effective for labour induction, but injection to abortion times are prolonged.
Preinsertion of multiple osmotic dilators 6 to 24 hours prior to amnio-infusion may reduce the time from induction to completion, reduce the risk of cervical laceration, and almost eliminate posterior wall rupture.
Prostaglandins (PGF2α, PGE1, PGE2) can be used for cervical ripening but may cause unsupervised delivery.
Another form of cervical preparation is the insertion of an Atad double balloon catheter; this method may also be used as a mechanical method of labour induction with similar end points (induction interval and complete abortion rates) to techniques with prostaglandins.
Techniques for Amniocentesis
The optimal site for amniocentesis is approximately 2.5 cm below the most prominent part of the uterus as palpated through the abdominal wall. The amniocentesis can be performed with a number 16 teflon extracath. Once the amniotic cavity is entered and the amniotic fluid is identified, the rigid central needle should be removed and drainage of amniotic fluid should continue. A pH test on the fluid will confirm its amniotic origin. The induction agent is then injected into the amniotic cavity. Ultrasound guidance may be necessary under some circumstances (e.g., if the patient is obese).
(a) Prostaglandin F2α (PGF2α) Amnio-Infusion
Intra-amniotic installation of PGF2α is an effective technique but may be associated with the need for a second injection, transient fetal survival, failure, and significant GI side effects. Pretreatment with laminaria tents can decrease the need for repeat injection, and pretreatment with prochlorperazine 10 mg IM or IV, or another antiemetic with loperamide (4 mg) orally one hour prior to amnio-infusion, will reduce the GI side effects.
A test dose of 5 mg of PGF2α is given over one minute to detect sensitivity to the drug or accidental intravascular placement of the needle. Then a total of 40 to 50 mg is given over a few minutes. Constant confirmation of the catheter's position in the amniotic cavity must be assured. An additional 20 to 40 mg may be required if the membranes are intact or if there is poor cervical effacement or inadequate uterine activity.
The absence or a decrease in the amniotic fluid volume as a result of ruptured membranes or genetic abnormalities may require an alternative route of prostaglandin administration.
(b) Hyperosmolar Urea Amnio-Infusion
Intra-amniotic hyperosmolar urea (80 - 90 gms/100 mL 5% dextrose in water for a 59.7% concentration) is effective for labour induction, but injection to abortion times are prolonged. Augmentation with PGF2α (5, 10, or 20 mg) administered with or immediately after the urea infusion decreases the interval from induction to abortion.
Following successful amniocentesis and the removal of 200 mL of amniotic fluid, the solution is slowly infused by gravity feeding.{pagebreak}
Written and revised by
Gerald Hurowitz, M.D.
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1. Low failure rates 2. Need for additional doses of PGF2α is almost eliminated 3. Expulsion of live fetuses is significantly reduced
Post Amnio-Infusion Care
Intravenous oxytocin should not be used before the delivery of the fetus unless the membranes are ruptured and there is no uterine activity. If there is no uterine activity, prostaglandin suppositories or intramuscular 15-methyl-prostaglandin are useful.
After the fetus is passed, the patient should be examined to determine if the placenta is in the uterus, the cervix, or the vagina. In the latter two circumstances the placenta should be removed. If the placenta remains within the uterus, the infusion of intravenous oxytocin, 80 to 100 U/L of lactated Ringer's solution is appropriate.
Observation to allow for spontaneous evacuation of the uterus can extend to eight hours if the patient is afebrile and bleeding is minimal. The patient should be examined periodically to check for the placenta within the vagina. If the placenta is retained beyond this period, the uterus needs to be evacuated using ring forceps. It is rarely necessary to go to the operating room.
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After all POC have been evacuated, the cervix should be examined for trauma.
(c) Extra-Amniotic Prostaglandin
Extra-amniotic PGF2α and PGE2 is safe and effective in the termination of second trimester pregnancies. This method is useful in cases of late second trimester abortion or when access into the amniotic cavity is difficult. A small 12-gauge Foley catheter is passed through the cervical canal and the bulb inflated with 15 mL of saline solution. The bulb is within the uterus but extra-amniotic. The small size of the bulb limits trauma to the extra-amniotic space and reduces the risk of intravascular infusion and hypertonic contractions. PGF2α, 0.5 to 1.0 mg diluted in saline is given intermittently and titrated to the severity of contractions.
There must be an interval between the cessation of prostaglandin infusion and the administration of oxytocin to decrease the risk of hypertonic contractions and the potential for uterine rupture.
(d) IM Carboprost (15-Methylprostaglandin F2α, Prostin/15M, Hemabate)
Carboprost is a synthetic 15-methyl form of PGF2α that is resistant to enzymatic degradation. As a result, carboprost is more potent, and has increased smooth muscle stimulation and longer duration of activity than PGF2α and PGE2. Thus it can be administered intramuscularly.
In patients not responding to conventional therapy, IM carboprost is successful in approximately 95% within 10 to 20 hours. The recommended dose for failed late second trimester termination is 250 ìg by deep intramuscular injection, with the dose repeated every two hours as needed. The total dose can range from 1250 to 2500 ìg. The use of multiple osmotic dilators should decrease the injection to abortion time.
Oxytocin should not be used concurrently with carboprost and should not be started until at least four hours after the final dose, unless the fetus has been passed.
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Indications 1. Failed second trimester abortion with conventional therapy (intra-amniotic PGF2α, oxytocin).
2. Termination of pregnancy in late second trimester and third trimester in cases with minimal or no amniotic fluid.
3. Refractory postpartum or post-abortal bleeding.
Advantages of Carboprost Versus Other Prostaglandins and Oxytocin
1. Higher potency allows more individualized dosing compared with intra-amniotic methods.
2. IM administration is less painful, easier, and less invasive, which reduces the risk of infection.
3. Carboprost can be used with ruptured membranes or in other situations with reduced amniotic fluid volume.
4. Carboprost allows the patient to be ambulatory for a longer period of time.
5. The non-term uterus responds to carboprost; therefore, induction of labour with intra-uterine demise can occur prior to spontaneous labour.
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Disadvantages. These include significant vomiting and diarrhea.
(e) Concentrated Oxytocin Infusion
Oxytocin has not been commonly used for abortion induction because it was thought not to be efficacious in gestations less than 24 weeks. However, administered with increasing concentration, oxytocin has been efficacious in achieving second trimester termination. Oxytocin 50 units in 500 mL 5% dextrose and normal saline is given over three hours, followed by one hour of rest. This is repeated, adding 50 additional units to the next 500 mL of infusion, and the pattern of infusion over three hours followed by one hour of rest is continued until the patient aborts or the maximum concentration of 300 units/500 mL is reached.
The mean induction to delivery interval is 8.2 plus or minus 5.1 hours.
(f) Misoprostol
Misoprostol can be used either orally or vaginally for uterine evacuation for fetal demise or second trimester termination; however, oral administration is associated with more GI side effects, such as nausea and diarrhea. {pagebreak}
In a study comparing misoprostol 200, 400, and 600 ìg given vaginally every 12 hours, the abortion rates were 70.6%, 82%, and 96%, respectively. (IA) Currently, vaginal misoprostol 200 ìg every 12 hours up to 48 hours appears to be the optimal regimen because as the doses increase or the interval of administration decreases, the number and severity of side effects increase. The incidence of abortion within 48 hours of this regimen ranges from 70.6% to 87.2%.
Further research is required to determine the optimal dose and frequency for second trimester termination.
Insertion of laminaria tents at the time of the first misoprostol dose did not alter efficacy. The use of laminaria tents prior to misoprostol, which may improve efficacy, has not been reported. The success interval from initiation to abortion and the failure rate are both increased in viable gestation compared with fetal demise.
Uterine rupture in women with previous Caesarean section has been reported; however, these occurred in gestations greater than 20 weeks and with higher doses or decreased frequency of infusion (200 - 400 ìg every 4 - 6 hours).
D&E Versus Induction
There are no prospective randomized studies comparing current methods for labour induction and D&E. Older studies that compare these methods and a more recent study indicate that D&E is associated with fewer complications than induction. The most frequent complication associated with induction was retained placenta. Of the induction methods, misoprostol was the most efficacious but still had more complications than D&E.
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One consideration in Canada is the lack of physicians who have the experience to perform advanced gestation D&E.
Hysterotomy and Hysterectomy
Hysterotomy is essentially an early classical Caesarean section. With current pharmacologic agents for labour induction in pregnancy termination, the procedure is rarely indicated as a primary method of abortion. The morbidity and mortality associated with hysterotomy are far greater than for any other technique. In most cases, failed abortions are managed with parenteral, oral, vaginal, or rectal prostaglandins even in the presence of a uterine anomaly.
Only after failure of the prostaglandins should hysterotomy be performed.
If pregnancy co-exists with a separate indication for hysterectomy (cervical, uterine, or ovarian cancer) then gravid hysterectomy may be indicated. However, a simpler means of pregnancy evacuation followed by a definitive diagnosis and therapy is preferred and will reduce the associated morbidity and mortality associated with gravid hysterectomy.
These guidelines were reviewed by the Clinical Practice - Gynaecology Committee and the Social and Sexual Issues Committee and approved by the Executive and Council of the Society of Obstetricians and Gynaecologists of Canada.
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