Second-trimester abortion can be performed via standard dilation and evacuation (D&E) or through medical induction with mifepristone and misoprostol. When reviewing the two options, most women prefer D&E.6,7 Few randomized studies directly compare induction to D&E because women are generally unwilling to be randomized; overall D&E is less painful and more acceptable than induction.7
Dilation and evacuation
D&E is the most common method of second-trimester pregnancy termination in the United States, accounting for more than 98% of all such procedures and nearly 95% of all abortions after 21 weeks.2 The procedure can be safely performed in the outpatient setting with appropriately trained providers and staff; hospital care is not necessary for most low-risk patients.4 D&E comprises two steps: cervical preparation and uterine evacuation.
The Society of Family Planning recommends cervical preparation in the second trimester to facilitate safe uterine evacuation.8 Cervical preparation can be accomplished with osmotic dilators, medications, or both in combination; the necessary amount of dilation depends on factors such as gestational age and parity. Cervical preparation decreases rates of uterine perforation and cervical laceration, especially in later gestations.8
In the early second trimester, misoprostol, a synthetic prostaglandin E1 analog, administered the same day as the D&E is usually sufficient for cervical preparation. It induces uterine contractions and cervical softening. Following misoprostol administration, the cervix is mechanically dilated with dilators, such as Pratt or Hegar dilators at the discretion and preference of the physician, until dilation is adequate for safe uterine evacuation. Common misoprostol regimens include 400 or 600 mcg administered 1.5 to 4 hours prior to the procedure by vaginal, buccal, or sublingual route.8
As gestational age advances, cervical osmotic dilators either alone or in combination with misoprostol are required for adequate cervical dilation. Osmotic dilators or tents are small, thin rods that radially expand as they absorb fluid. The proximal end of the dilator is placed through the internal os with the distal end visible at the external os. The most well-known osmotic dilator is the dehydrated sterilized seaweed Laminaria japonicum, commercially available in standard sizes. One or more Laminaria tents are retained at least 12 hours, usually overnight, to achieve full dilation. More Laminaria tents and serial sets of dilators may be needed for abortions at more advanced gestational ages. The synthetic hygroscopic dilator Dilapan-S expands more quickly and is used for same-day or multiple-day cervical preparation. Dilapan-S dilators are more expensive than Laminaria tents, although fewer Dilapan-S are needed to accomplish the same cervical dilation. The choice and number of dilators is at the discretion of the surgeon as no minimum number, standard or preferred combination of osmotic dilators has been established for any gestational age.8
Mifepristone, an antiprogestogen that causes cervical softening and dilation, is a potent addition to cervical preparation. A combination of mifepristone and osmotic dilators is often used in the late second trimester; beyond 19 weeks, mifepristone 200 mg orally at the time of dilator placement increases ease of the D&E procedure.9 Mifepristone is better tolerated than adjunctive misoprostol, which may cause pain, fever, and chills.9 Although the complication of infection with surgical abortion is low, antibiotic prophylaxis reduces the risk; the American College of Obstetricians and Gynecologists recommends a single dose of doxycycline 200 mg orally at the time of surgical abortion, typically administered when dilators are placed.10
In case you missed it: Three steps to provide mifepristone
D&E is performed after adequate cervical dilation is achieved, either the same day or up to 2 days later, depending on the extent of cervical preparation needed. A large suction cannula, usually a size 14 or 16 at and after 16 weeks’ gestation, is used to drain the amniotic fluid and the pregnancy tissue is removed using a combination of instruments and suction. Bierer or other modified ovum forceps facilitate uterine evacuation. Risk of significant bleeding during D&E is reduced by adding vasoconstrictive agents such as vasopressin to a paracervical block and by administering oxytocin 30 units intravenously over 15 minutes during the procedure.11,12 Routine intraoperative ultrasound guidance decreases rates of uterine perforation, especially in the training setting.13
Just as with use of mifepristone for cervical preparation for D&E, pretreatment with mifepristone 200 mg orally 24 to 48 hours prior to induction prepares the cervix and improves success rates of medical abortion in the second trimester. Compared with simultaneous administration or placebo, mifepristone pretreatment leads to much shorter (up to 50%) induction times; 95% of women deliver within 24 hours of starting the induction.14,15 Placement of cervical osmotic dilators at the time of induction does not shorten overall procedure time.16
Misoprostol is the most commonly used medication for second-trimester induction abortion. While several regimens have been studied, a frequent misoprostol dosing interval of every 3 hours shortens the overall induction time; 400 mcg appears to be the minimum effective dose. Vaginal and sublingual routes of misoprostol are superior to oral administration.16 Reported rates of intervention for bleeding or retained placenta vary; with these evidence-based medication regimens, the rate of retained placenta is as low as 6%.15
The authors report no potential conflicts of interest with regard to this article.
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