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Implantation of spinal cord stimulators in women of childbearing age requires special consideration of future obstetric and anesthetic needs. The technical considerations with regard to lead insertion as well as the IPG implantation are important to allow for smooth anesthetic and obstetric care. First, whenever possible, the access to the epidural space for lead placement should be in the upper lumbar to low thoracic levels. Avoiding lower lumbar levels will facilitate neuraxial anesthetic techniques that are preferable in caring for the parturient. Second, abdominal placement of the IPG may result in both technical and biologic complications. The IPG may easily be damaged during an urgent/emergent cesarean delivery by either direct surgical trauma or EMF from the electrocautery. In the case series of sacral neuromodulation by Wiseman et al., abdominal placement of the IPG required repositioning during pregnancy because of progressive pain that was likely related to increased abdominal girth (4). In a review of cardiac pacemakers, Jaffe et al. reported ulceration of an abdominally placed IPG with advancing pregnancy (5). In both cases presented here, buttock placement of the IPG did not pose any clinical issues and the device was not damaged during the delivery of obstetric care.
Deactivation of rechargeable systems for the purpose of pregnancy did not result in any negative consequences to the function of the IPG. In case one, the IPG uses nonvolatile memory which prevents the loss of stored data and programs when all power is lost. Furthermore, even when the battery is overdischarged, the negative electrode does not dissolve and so the battery capacity remains stable (6). In the second case, the IPG was turned off when the patient still felt paresthesia. Even if there was the lowest voltage remaining (3.5 V) in the IPG, there would not be enough time in an average 40-week pregnancy to cause overdischarge and therefore decrement in IPG functional output (7). In short, present day constant current IPGs when deactivated for pregnancy are unlikely to undergo permanent capacity depletion requiring replacement because of a dissolving negative electrode.
There remains uncertainty about the impact of SCS on fertility. Our second patient and the five patients reported by Wiseman et al. all had active neuromodulation during conception without reported issues of fertility. Based on the current accepted biochemical mechanisms of SCS in pain control, none are hormonally mediated ( 8 ). Evers et al. studied the effect of repetitive transcranial magnetic stimulation (rTMS) in the treatment of affective disorders on neuroendocrine hormone levels, including cortisol, prolactin, follicle stimulating hormone, and thyroid stimulating hormone (9). They reported no change in the serum levels at the typical setting used in the treatment of depression. There are many published animal studies investigating the effects of EMF on reproduction and fetal development. Brent reviewed 58 in vivo and in vitro animal models studies evaluating the reproductive and teratogenic effects of low-frequency EMF (10). The effect on fertility was out assessed in seven of those studies. While one study showed inconsistent effects on fertility, the remaining studies all concluded no adverse effects of low-frequency (less than 3000 Hz) EMF on fertility. Anecdotally, neuromodulation may indirectly cause a relative increase in fertility by reducing pain, enhancing activity and sense of well-being thereby promoting sexual activity.
The current recommendation in a patient with a neuromodulatory device for chronic pain is deactivation once the diagnosis of pregnancy is made. There are no studies examining the effect of SCS on human fetal development, and it is very unlikely that any will be undertaken. Available literature consists of studies investigating the effects of electrical exposure in the parturient through accidental electrical injury, electrocardioversion for arrhythmias, and proximity of electrical devices with their associated EMF. Early case reports of 15 pregnant women receiving electrical shock between 1965 to 1992 resulted in a 73% rate of fetal demise with no maternal deaths (11–15). More recently, a prospective cohort study of 31 women who received varying degrees of electrical shock during pregnancy demonstrated that 28 of the women gave birth to healthy newborns, one woman had a newborn with a ventricular septal defect, and the remaining two women had spontaneous abortions (16). Among their age-matched controls subjects, 30 had healthy babies and one had a spontaneous abortion. The small number of patients precludes strong conclusions; however, the increase in cardiac defect raises concerns.