We present a combined obstetric and respiratory perspective on two pregnancies for a woman with severe Type 2 Spinal Muscular Atrophy (SMA). Our patient had the lowest prepregnancy weight (20 kg) and vital capacity of 0.34 L (VC 11% predicted) yet to be reported in the sparse literature on pregnancy with SMA. She delivered two live healthy infants via planned caesarean section without pregnancy or neonatal complication. We describe the respiratory and obstetric management techniques used for a pregnancy with this degree of respiratory compromise.
Spinal Muscular Atrophy (SMA) has an incidence of 1/6000–1/10000 and a carrier frequency of 1/40 to 1/50 [
We report two successful pregnancies in a woman with Type 2 SMA, with a vital capacity (VC) of 0.34 L (11% of predicted value [
A 32-year-old woman presented to a high-risk pregnancy clinic in her first ongoing pregnancy. Developmentally, her milestones had been classically delayed, crawling at age one. She slowly developed severe contractures of her limbs and severe kyphoscoliosis throughout her teenage years. At age 17, she presented with compensated hypercapnic respiratory failure (pH 7.41,
Antenatal booking weight was 20 kilograms, and the patient was wheelchair dependent and kept upright by means of a neck brace, with movement only of her left wrist and left fingers. Clexane thromboprophylaxis was commenced given her immobility (10 mg daily). The couple declined invasive genetic testing for SMA. First trimester screening gave a risk of approximately
Outpatient respiratory monitoring was performed every second week from week 10 to 22, then weekly from week 22 to 26, including VC and peak cough flow rates. Sequential inspiratory and expiratory muscle strength measurement were attempted, but the patient did not have significant effort to register a measurement consistently. Baseline (10 weeks) ABGs were attempted, but abandoned due to the difficulty in obtaining a sample secondary to severe contractures in her wrists, elbows, and hips. For this reason, routine serial ABGs were not performed and due to a lack of equipment, end-tidal
Using the patient’s own volume ventilator (VS
Respiratory function remained stable during the pregnancy, with VC ranging between 0.22 to 0.30 L and
Vital capacity (VC) (solid line) and room air oxygen saturations (
First pregnancy: week from gestation versus vital capacity and
Second pregnancy: week from gestation versus vital capacity and
Planned admission took place at 26 weeks gestation for daily respiratory observation and preparation for delivery by planned caesarean section at 28 weeks. The indication for mode of delivery was a combination of prematurity, kyphoscoliosis, anticipated cephalopelvic disproportion, and primiparity. The gestation was chosen as the best balance of fetal respiratory maturity and maternal respiratory function, anthropometry, home equipment constraints, and patient’s preference for level of NIV dependency. Respiratory status was stable with
At caesarean section, epidural space cannulation was successful yet the sensory block was unsatisfactory for the level of surgery, potentially due to a partial occlusion of the epidural space related to her severe kyphoscoliosis. Consequently, a general anaesthetic was administered with the assistance of mouthpiece volume ventilation to assist breathing during the awake fibre-optic nasal intubation. During the process of the intubation, supplemental oxygen was not required to be entrained through the mouthpiece ventilation, as transient falls in saturations were caused by suboptimal ventilation which occurred when the mouth piece seal was lost during moments of anxiety. This was instead corrected by manually assisting with the patient’s mouthpiece seal, promoting calm in the patient and by increasing the volume being delivered by the ventilator (from 0.35 to 0.45 L) to cope with transient leaks. A midline abdominal incision was performed for access due to the kyphoscoliosis, with minimal subcutaneous fat and an atrophied rectus abdominis muscle being noted. An uneventful lower segment caesarean section was performed with delivery of a live female infant (Apgars of 7 at 1 minute, 9 at 5 minutes, birth weight 1.054 kg).
The patient was transferred to the intensive care unit (ICU) and extubated directly onto her noninvasive ventilator four hours later. Postnatally, respiratory function remained stable with room air
An unplanned second pregnancy was confirmed eight months later, with late presentation at 19 weeks gestation. Between pregnancies, there had been further deterioration in the patient’s neuromuscular condition, with loss of left hand function removing control of her electric wheelchair. On first presentation, VC had fallen to 0.27 L (8% predicted). The antenatal care plan was duplicated between pregnancies. Respiratory function remained stable during the pregnancy (VC 0.24 to 0.32 L and
At 28 weeks and after steroid cover, an elective classical caesarean section with bilateral tubal sterilization (at the patient’s request) was performed through the previous vertical abdominal midline incision. An elective awake mouthpiece-assisted fibreoptic intubation general anaesthetic was performed. A live, male infant was delivered (Apgars of 6 at 1 minute, 7 at 5 minutes, 8 at 10 minutes, birth weight 1 kg). Postoperatively, the patient was admitted to ICU, where she was extubated on to NIV three hours later and discharged to the obstetric ward two days later. During this time there was a minor increase in sputum which was coughed out effectively after volume ventilator insufflation and using manual assist techniques (ptussive squeeze). Oxygen saturations on room air remained
In normal pregnancies, total lung capacity is preserved with a small reduction in residual volume which generally stabilises or mildly enhances the VC. The major change in normal lung volumes is the reduction in functional residual capacity due to a reduction in chest wall compliance, starting early second trimester and worsening as the pregnancy progresses to a 35% to 40% decline [
For ongoing SMA pregnancies, antenatal care centres around maternal respiratory function, with NIV being shown to reduce respiratory compromise [
The importance of avoiding routine mask-oxygen prescription (without mechanical ventilation) in patients who are desaturating due to alveolar hypoventilation should be emphasized. In these scenarios supplemental oxygen alone can lead to reduced ventilatory drive,
In order to assess the adequacy of ventilation, a measure of
During the outpatient period, SpO2 levels were measured weekly at one or two intervals. At this frequency of monitoring, a detection of respiratory deterioration may have been missed or delayed. In patients with access to domiciliary oximetry, acting on
Obstetric care during this pregnancy revolved around close regular obstetric surveillance, ongoing respiratory team review, admission for intensive observation, and a multidisciplinary decision regarding the optimum gestation for delivery. The latter decision is most likely to be open to discussion. In the absence of published literature on the precise effects of advancing gestation in a woman with Type 2 SMA weighing just 20 kg and with a VC of 11% predicted, it was difficult to be certain how much further incapacitation could be withstood before the mother’s respiratory status was put at risk. Whilst it is feasible to provide continuous ventilatory support via daytime mouthpiece ventilation and nocturnal mask ventilation in patients with very low VC throughout pregnancy [
Anaesthetic review prior to labour and delivery is essential due to the respiratory compromise in SMA and the associated difficulties with both regional and general anaesthesia. Failed regional anaesthesia due to spinal column deformity is not uncommon in SMA, and the usefulness of subsequent awake fibreoptic technique has been reported [
A literature review was performed by searching MEDLINE from 1950 to August 2008 using key words “spinal muscular atrophy”, “SMA,” and “pregnancy”. Seventeen case reports describing a total of 33 pregnancies were identified. The largest review was of 12 females with 17 infants [