Abortion performed in the middle months of pregnancy, i.e. 13-24 weeks is a significantly different procedure from the first trimester. Although there are similarities, as pregnancy progresses through the second trimester, the procedures used require greater time, skill and entail somewhat greater risk, though still significantly lower than carrying a pregnancy to term.
The essential difference is that the cervix must be dilated to increasing diameters with increasing stage of pregnancy. The extent to which the cervix can be safely dilated with dilators varies, generally being easier in women who have delivered children previously. Most experienced physicians will avoid the use of mechanical dilators beyond the 14th week of pregnancy. Some will avoid them after the 10th week. As a general rule, the method of choice for dilating the cervix beyond the 12th week is osmotic dilators.
These are basically stalks of material that absorb water and expand once placed inside the cervix. Once they have been inserted they are left in place anywhere from six hours to overnight. The result is that the cervix is both dilated and softened with little risk of the damage that might occur if wide dilation were to be attempted with mechanical dilators.
In more advanced stages of pregnancy, varying from 20-23 weeks and beyond, dilatation is generally accomplished in a serial fashion. This involves the insertion of a number of osmotic dilators for 6 or more hours to dilate the cervix adequately to insert 10 to 20 or more osmotic dilators followed, usually the next day with the Evacuation (“E”) of D&E of the uterus. This stage of surgery, as in the first trimester procedure is usually performed under sedation combined with local anesthesia. The fetus and placenta are generally removed with forceps, usually followed with suction curettage to remove debris. Sharp curettage may or may not be performed as a final step.
An alternative to this procedure in the mid-trimester and beyond is induction of labor. There are a variety of procedures available to accomplish this end, but in general they all involve stimulating the uterus to contract much the same way as it does in a spontaneous term labor. This approach would seem at first to be ideal, since it may involve no instrumentation and is totally natural.
In reality, however, the uterus is frequently very much disinclined to labor at these early stages, and even when it does, the cervix may be very disinclined to dilate. There are a variety of options for “induction”.
The technique current in commonest use involves a group of drugs called Prostaglandins. These are administered either in the cavity of the uterus by injection or in the vagina as a gel or suppository. These may be used in conjunction with osmotic dilators as well.
There is some controversy as to which of these techniques is the safest. Most available data suggest that prior to 20 weeks gestation, D&E offers greater safety and efficacy. Beyond that stage, there is probably inadequate data to prove either is superior.
We believe that experience is the primary determinant of safety in the later stage procedures. In experienced hands, we believe that D&E is preferable. It is more predictable and entails less serious risk. The final alternative is “hysterectomy” which is basically an early cesarean section.
This procedure is best reserved for situations where emptying the uterus by the vaginal route is not possible. It has the disadvantages of greater risk, greater pain, greater recuperation, and higher cost and perhaps of greatest significance, it precludes future vaginal birth.