3.1

Pre-pregnancy

Pre-pregnancy obesity has been linked to infertility. A proposed mechanism is dysregulation of the hypothalamic-pituitary-ovarian axis with associated changes in ovulatory release and lack of a normal menstrual cycle [ ]. Endocrine dysfunction has been associated with a reduction in successful conception per cycle [ ], subfertility, prolonged periods of reduced fertility and unwanted non-conception, and infertility [ ]. Endometrial implantation may also be negatively impacted by obesity resulting in prolonged time to conception, an increased miscarriage rate, and a lower success rate with nearly all assisted reproductive therapies [ ].

3.2

Antepartum and peripartum

The comorbid conditions associated with obesity before and during pregnancy include, but are not limited to, gestational diabetes mellitus (GDM), hypertensive disorders of pregnancy (HDP), psychiatric diagnoses including depression and anxiety, and increased rates of preterm birth, labor complications, and cesarean delivery [ ].

There are a variety of mechanisms that may explain why obese pregnant people develop GDM at higher rates, especially among those that belong to racial and ethnic groups other than non-Hispanic White women [ ]. Among these are increases in baseline inflammation, decreased insulin response, and an increase in insulin resistance [ ]. These pathophysiologic changes worsen during pregnancy and have been linked to a much higher risk of diabetes mellitus in the decades following pregnancy [ ]. GDM is also associated with a greater likelihood of developing gestational hypertension [ ].

Obesity is also associated with higher risk for HDP, both gestational hypertension and preeclampsia. This relationship has been demonstrated in multiple studies and the risk is up to four times higher in women with class II or class III obesity relative to class I [ , ]. While the underlying etiology remains unknown, insulin resistance and chronic inflammation are suspected to play a part in this association [ ].

Despite recent campaigns to advocate for acceptance of people with a larger body habitus, many patients who are obese suffer from a negative stigma associated with their size. Women who experience these interactions on a regular basis report a higher level of stress, demonstrate more destructive eating habits, and note more depressive symptoms [ ]. Studies have a found an association between obesity and maternal depressive symptoms and anxiety in both antepartum and postpartum women [ , ]. Women with poor mental health also struggle with obesity, suggesting that the association may be causal starting from either primary problem [ ].

Obesity has also been shown to be an independent risk factor in severe maternal morbidity and mortality when compared to women of normal BMI [ , ]. This relationship has been demonstrated in several countries including the United Kingdom [ ], Ireland [ ], and the US [ , ].

Studies have also demonstrated that obese parturients are at higher risk complications of labor including need for labor induction, augmentation with oxytocin, failure to progress labor, and assisted vaginal delivery when compared to normal BMI parturients [ ]. Obese parturients with a BMI ≥35 also experience shoulder dystocia at a rate 200% higher than parturients with BMI below 35 [ ]. A contributing factor to the risk of shoulder dystocia in obesity is the relationship between elevated BMI and post-term birth; women with a BMI of 50 or more are nearly twice as likely to deliver post-term [ ].

It is well documented that obesity increases the chance of unscheduled cesarean delivery [ , , , ]. When compared to those with normal BMI, obese parturients are twice as likely to undergo cesarean delivery and risk increases with increasing BMI [ , ]. The presence of preexisting comorbidities, decreased cervical dilatation rate and failure to progress, increased concern for fetal shoulder dystocia, and excessive pregnancy weight gain are likely contributing factors [ , ]. While cesarean delivery may mitigate some risks of vaginal delivery, studies show that obese parturients are also at increased risk for surgical complications including anesthesia-related morbidity, postpartum endometritis, poor wound healing, surgical site infection, hemorrhage, and lower success for subsequent vaginal birth after cesarean delivery [ ].

3.3

Fetal implications

Myriad congenital anomalies have been associated with maternal obesity with an established direct correlation of risk with increasing BMI. This has been demonstrated for fetal neural tube and cardiac defects [ , ]. Furthermore, early detection and counseling can be hindered by maternal obesity; central adiposity can reduce the ability of ultrasound-based detection of intrauterine fetal anomalies [ ].

Fetal macrosomia (birth weight >4000 g) and large for gestational age (LGA) (birth weight >90% percentile for gestational age and sex) have been positively associated with obesity in multiple meta-analyses, with higher classes of obesity compounding this effect [ , , ]. One study reported that obese parturients are more than twice as likely to have associated fetal macrosomia or a LGA fetus when compared to parturients with normal BMI [ ]. Not surprisingly, these positive associations between maternal obesity and fetal size are protective in lowering the odds of low birth weight and small for gestational age (birth weight <10% percentile for gestational age and sex) fetuses [ ].

Several meta-analyses report up to a two-fold increased risk of stillbirth for obese parturients; this risk is more pronounced in the antepartum compared to the intrapartum period [ , , , ]. The comorbidities associated with obesity in pregnancy may contribute to the risk of stillbirths [ ]. Approximately 5% of stillbirths have associated fetal congenital malformations and as previously noted, these anomalies can be harder to detect by ultrasound in the obese parturient [ ].

3.4

Postpartum

Two separate studies reported an association between obesity and postpartum hemorrhage [ , ], however a meta-analysis did not reach the same conclusion [ ]. An increase in the volume of distribution for uterotonic agents, challenges in performing thorough fundal and bimanual exams, and increased uterine size due to post-term deliveries and LGA fetuses have been proposed as hemorrhage-specific risk factors in obese parturients [ ].

Surgical-site infections (SSI) post-cesarean delivery occur twice as frequently for obese women compared to normal BMI parturients [ , ]. SSI are a leading cause of sepsis among obese parturients [ , ]. The American College of Obstetrics and Gynecology recommends that patients receive a first-generation cephalosporin within 60 min prior to skin incision for the prevention of SSI with a standard 2-g dose; increased rates of SSI among obese patients may be due in part to subtherapeutic antibiotic prophylaxis [ ]. Dosing should be adjusted for patients that weigh greater than 100 kg to 3 g cefazolin. Some institutions recommend that cefazolin dosing is increased based on a BMI threshold, but the evidence to support this practice is not well established [ ]. In addition, intravenous azithromycin 500 mg is recommended for patients who have labored or who have rupture of membranes to prevent endometritis, but to date no dosing recommendations for higher BMI have been made for azithromycin [ ].

The risk of venous thromboembolism (VTE) has been reported to be four-times higher in parturients with a BMI of 40 kg/m ² or higher compared to non-obese parturients [ ]. Postpartum VTE was more strongly associated with pre-pregnancy BMI than the BMI at delivery. However, both significant pregnancy weight gain (>22 kg) and cesarean delivery increased the risk of VTE independently, and their combined effect amplified the risk. Postpartum anticoagulation strategies for the prevention of VTE have not been studied in randomized, controlled trials, and so practice has been based on society recommendations and institutional protocols. Patient selection and dosing is based on BMI, weight, and the presence of other risk factors [ ].

4.1

Identification of the neuraxis

The majority of lumbar neuraxial techniques in obstetrics are performed with a midline approach. Identification of the midline can be challenging in obese patients, and most providers prefer that obese patients are seated for the procedure. Usually thoracic spinous processes are palpable, though palpation of lumbar spinous processes can prove more difficult. Utilizing patient input to identify the midline can be helpful. With proprioception, where the patient is asked to touch the midline of their own back, the accuracy of identification of the midline in a non-obese population was within 1.6 mm (of midline determined by palpation) with a range of −29 to 27 mm [ ]. Proprioception can be less feasible for obese patients; identification of the midline by light touch by the provider is more accurate. This is performed by the provider starting with light touch laterally and slowly moving towards the midline. Using this technique, the midline was correctly identified in 100% of patients in one study and the mean deviation was 0 mm with a range of −10 to 11 mm [ ]. Ultrasound is the most accurate method to identify the midline. Effective use of lumbar ultrasound prior to a neuraxial techniques in obese patients requires training, with sufficient expertise obtained by first performing scans in patients with lower BMI.

Identification of the correct lumbar interspace using landmarks is highly inaccurate. In a non-obstetric population, lumbar levels identified by clinical landmarks were compared with MRI. Fewer than 30% of landmarks were at the correct level; only 3% were lower than actual level, 51% were one level higher, and 15.5% were two levels higher [ ]. Deviation from the true anatomic level was more frequent in obese patients. A retrospective study in parturients with BMI of 50 kg/m ² and above compared documented level of epidural insertion with postoperative radiographic images performed to exclude retained foreign objects. Seventy percent of catheters were placed at a higher level than estimated by the anesthesiologist and 21% (95% CI 15–29%) were above L1/L2 [ ]. In this study, the use of ultrasound was not protective as the proportion of catheters above L1/L2 was 28% using ultrasound and 17% without ultrasound [ ]. Importantly, this was a retrospective study, and it is unclear whether ultrasound was used to identify midline alone, or also the level of insertion. In our experience teaching neuraxial ultrasound, identification of the midline and location of the correct lumbar level are quite easy to learn, while estimation of the depth of the epidural space is more challenging. The use of ultrasound before spinal anesthesia for cesarean delivery in parturients with a BMI ≥35 kg/m ² reduced procedure time and the number of needle passes, while this was not the case in women with a BMI below 35 kg/m ² [ ]. If ultrasound is used to estimate the depth of the ligamentum flavum, compression of the subcutaneous tissue by the ultrasound probe has to be taken into account. It is advisable to try and exert similar pressure with the preprocedural ultrasound probe as one uses during the neuraxial procedure.

4.2

Neuraxial labor analgesia

In general, an epidural catheter should be placed early in labor to avoid time pressure and maximize patient collaboration. Since identification of the epidural space is more challenging in obese women, a technique with indirect confirmation of the epidural location of the needle tip is often recommended. A combined spinal epidural (CSE) technique allows one to identify the subarachnoid space with a small gauge atraumatic spinal needle through a Tuohy needle located in the epidural space. With the traditional CSE technique the initial analgesic dose is given intrathecally, followed by placement of an epidural catheter for administration of the maintenance dose. More recently, the technique of dural puncture epidural (DPE) has been introduced [ ]. Like the CSE, in the DPE an atraumatic spinal needle is advanced into the subarachnoid space and the flow of CSF confirms midline (and epidural) placement of the Tuohy needle. Unlike the CSE, there is no intrathecal injection and the initial analgesic dose is given through the epidural catheter. The hole in the dura mater facilitates drug transfer with shorter time to pain relief, potentially leading to improved sacral analgesia and less motor block in DPE compared to the epidural technique [ ]. The size of the spinal needle seems to be important, as DPE with a 26-gauge spinal needle did not replicate the results seen with 25-gauge needles [ ]. The DPE technique is also associated with less pruritus and less hypotension or uterine hypertonus when compared with CSE. Nevertheless, the possibility to confirm midline position of the epidural needle through flow of CSF can be advantageous in patients with difficult landmarks, such as obese patients. Despite this theoretical advantage, a prospective comparison of DPE with a standard epidural technique in obese parturients did not reveal a difference in failure rates [ ]. Failure rates in this population were 30% and 26% for DPE and standard epidural, respectively [ ]. However, a separate retrospective study in super-obese parturients with a BMI ≥50 kg/m ² compared failure rates of the epidural technique with CSE vs DPE initiation [ ]. Failure rate was 28.6% (95% CI 18.9–40.7%) after epidural and 9.2% (95% CI 5.5–14.7%) after CSE or DPE [ ]. These results must be interpreted with caution, as the authors allocated patients for whom CSE or DPE failed to produce CSF to the epidural group. In such patients the initial catheter may have not been midline or may have not been within the epidural space. Inability to attain CSF after CSE or DPE are associated with a higher risk of catheter failure, and it is advised to repeat the procedure in these situations. Catheters placed after successful CSE have shown lower failure rates compared to epidural techniques when used for extension to cesarean delivery anesthesia in a non-obese population [ , ]. Due to the lack of data it is unclear if the same is true for DPE. Almost 30% of the failed catheters in the CSE/DPE group were attributed to migration of the catheter, i.e., catheter failure after satisfactory analgesia. One third of these super-obese women in this study delivered by cesarean delivery and the labor epidural catheters failed in only 5% of patients (95% CI 2.0–12.5%) [ ].

The use of intrathecal catheters has been suggested as an alternative technique to epidural catheters in obese parturients. Besides the risk of PDPH due to the larger needle size, intrathecal catheters may not be more reliable than epidural catheters [ ]. The most important drawback is the risk of inadvertent injection of an epidural dose into an intrathecal catheter with subsequent total spinal anesthesia. In cases of ADP, an intrathecal catheter is a valuable option if the technique was technically challenging. The intrathecal catheter must then be explicitly labelled and all team members including midwives and obstetricians should be informed.

Irrespective of the chosen method, catheter fixation to the skin in patients with obesity benefits from additional consideration. When patients change from the sitting flexed position to a sitting upright position the distance between the skin surface and the epidural space is increased due to a change in the thickness of the subcutaneous tissues. The extent of catheter movement is larger in obese parturients and has been shown to be as much as 4.3 cm [ ]. If the catheter is fixed to the skin while the patient is still in the flexed position, it can become dislodged from the epidural space when the patient changes position. It is therefore important to adjust the depth of the catheter while in the flexed sitting position and the to ask the patient to change into an upright sitting position or to move the patient to the lateral position before the catheter is fixed to the skin while maintaining the sterility of the catheter.

Maintenance of epidural labor analgesia is not different in obese vs. non-obese parturients. Manual boluses, continuous infusion, patient controlled epidural analgesia (PCEA) or programmed intermittent epidural boluses (PIEB) are all valuable options. An up-down sequential allocation study to determine the minimal effective labor epidural dose in 50% (ED50) of obese and non-obese parturients utilizing a solution of bupivacaine 0.1% without opioids showed that the ED50 was significantly lower in the obese group by a factor of 1.68 (95% CI 1.32–2.29) [ ]. In this study where obesity was defined as BMI above 30 kg/m ² , obese parturients required a reduced epidural dose relative to non-obese parturients to maintain adequate labor analgesia. This finding validates the use of a maintenance technique with patient controlled analgesic supplementation, i.e. PCEA, for titration of epidural labor analgesia.

Following epidural placement, satisfactory labor analgesia must be assessed regularly with a low threshold for timely replacement of poorly functioning catheters [ ]. A functioning catheter increases the chance to successfully convert a labor epidural catheter for intrapartum cesarean delivery which confers an additional level of safety.

4.3

Neuraxial anesthesia for cesarean delivery

Positioning, vascular access, neuraxial techniques, airway management and surgical procedures may all be more challenging in obese patients. Neuraxial anesthesia has the clear advantage of minimizing the risk of airway manipulations. There must be close communication with the surgeons in planning the cesarean delivery. The anesthetic plan is influenced by the intended surgical approach. Depending on the size of the panniculus, the incision may be a traditional Pfannenstiel incision, infraumbilical transverse, supraumbilical transverse, or supraumbilical vertical incision. A need for extra time for positioning of the patient and from incision to delivery, as well as the completion of surgical procedure must be anticipated and a single-shot spinal may not provide adequate anesthesia for the duration of the procedure. A single shot spinal with a 25- or 27-gauge atraumatic needle can also be challenging to perform in obese parturients, due to a lack of stability of the needle in soft adipose tissue. The spinal needle is difficult to direct into a specific direction and the reduced stabilization by surrounding tissue allows bending or even kinking of the needle. The use of a longer ‘introducer’ can facilitate redirections of the spinal needle. A 17g epidural needle is often the most suitable ‘introducer’ to guide the spinal needle in the correct direction. If using an epidural needle as a guide for the spinal needle, it is reasonable to insert an epidural catheter after spinal dosing, for a CSE technique.

There has been some debate about intrathecal dosing requirements in obese parturients and a dose regulation has been suggested. In a randomized trial, seven doses of intrathecal bupivacaine between 5 and 11 mg with 10 μg fentanyl and 0.2 mg morphine were studied in parturients with a BMI of 40 kg/m ² or higher, scheduled for elective cesarean delivery [ ]. The ED50 for surgical success, defined as no need for epidural supplementation, was 9.8 mg (95% CI 8.6–11 mg), slightly higher than the ED50 for a historic control in non-obese parturients [ ]. The authors advocate against doses below 10 mg bupivacaine and strongly recommend the use of CSE in an obese population.

In a retrospective study of almost 400 parturients who underwent elective cesarean delivery, spinal anesthesia was the most frequently performed anesthetic technique for patients with a BMI below 50 kg/m ² , while spinal anesthesia was never used for BMI ≥60 kg/m ² [ ]. Neuraxial failure rate was the lowest with spinal anesthesia (6.1%, 95% CI 3.2–10.4%), followed by epidural (8.6%, 95% CI 3.5–17%) and CSE (14.7%, 95%CI 8.8–22.5%). Most failures were identified before start of surgery and a second neuraxial technique was used in 85% of patients [ ]. The general anesthesia conversion rate was 1.3% (95% CI 0.4–2.9%).

Knowledge of the planned surgical technique can reduce the risk of neuraxial failure. For planned supraumbilical horizontal or vertical incisions a low thoracic epidural catheter at T12/L1 is recommended. This is combined with either a single shot spinal or with a CSE or even intrathecal catheter usually at the level L3/4 [ , ]. The low thoracic epidural catheter is then also used for postoperative pain control.

5.1

Obstructive sleep apnea

OSA in pregnancy has gained attention in the last decade. Several large retrospective database studies and one large prospective study associated OSA with adverse maternal and neonatal outcomes [ ]. Increased rates of OSA are seen among parturients with a BMI ≥30 kg/m ² , and OSA rates increase with increasing BMI [ , ]. Rates of OSA among obese parturients have been reported as high as 64% in some cohorts [ , ]. One large prospective study of OSA in pregnancy described a higher burden of OSA among non-Hispanic Black and Hispanic women but suggests that the effect may be more directly related to obesity in those racial and ethnic groups [ ]. OSA is also associated with increased rates of maternal morbidity and mortality and complications of anesthesia [ ]. The intersecting risks of respiratory and anesthetic complications associated with obesity, preeclampsia, and OSA in can be both additive and dynamic in obese women during pregnancy and peripartum. Anesthesiology consultation during pregnancy for high-risk patients such as those with BMI ≥40 kg/m ² or OSA with written care plans can help mitigate some of these risks [ ]. Recent society guidelines have been developed to guide the screening, diagnosis, and treatment of OSA in pregnant populations, and recommend screening pregnant women with BMI ≥30 kg/m ² for OSA [ ].

Co-morbidities and complications associated with OSA in retrospective and prospective studies include HDP, GDM, cardiomyopathy, congestive heart failure, pulmonary edema, pulmonary embolism, stroke, cesarean delivery, cesarean hysterectomy, postoperative wound complications, intensive care unit admission, increased hospital length of stay, mechanical ventilation or tracheostomy, acute respiratory distress syndrome, and in-hospital mortality [ , , ]. Despite calls for screening high-risk groups, there is no evidence to date that treatment of OSA mitigates the risk of these adverse outcomes. However, treatment of OSA is associated with many other health and quality of life benefits [ ].

The use of opioid medications and sedation in obese parturients has raised concern among clinicians, given the higher prevalence of airway obstruction due to airway morphology and increased rates of OSA in this population. Neuraxial opioids were associated with the risk of delayed respiratory depression in historical cohorts of non-obstetric patients and closed claims analyses. The incidence of opioid-induced respiratory depression is 0.04%–0.5% as indicated by need for naloxone administration and 23%–41% using hypoxemia or bradypnea as the clinical indicator among surgical patients [ ].

The use of neuraxial morphine or diamorphine in obstetric patients has been the gold-standard for post-cesarean delivery analgesia with excellent safety records in modern low (0.05 mg–0.15 mg intrathecal or 1–3 mg epidural morphine) or ultra-low doses (≤0.05 mg intrathecal or ≤ 1 mg epidural morphine) [ ]. A randomized double-blind comparison study suggests that 0.25 mg intrathecal diamorphine is similar in efficacy and side-effect profile to 0.1 mg intrathecal morphine (low-dose) [ ]. Concern has remained regarding the use of neuraxial morphine in high-risk patients, such as those with obesity or OSA, but recent analyses of large cohorts of patients that underwent cesarean delivery and received neuraxial morphine or diamorphine at low or ultra-low doses suggest that neuraxial morphine in low-doses is safe in obese obstetric patients (less than 0.15 mg intrathecal morphine or 0.25 mg diamorphine) [ ]. Guidelines promote the use of low- or ultra-low doses neuraxial morphine in obese women (BMI >40 kg/m ² ) for cesarean delivery analgesia with careful postoperative monitoring, and careful consideration of individual patient factors that may increase the risk of respiratory depression such as concomitant use of sedating medications including magnesium and/or co-existing co-morbidities such as preeclampsia and OSA [ ]. Current guidelines advocate adherence to the American Society of Anesthesiologists guidelines for respiratory monitoring following neuraxial morphine for high-risk patients such as those with obesity and OSA [ ]. This includes a minimum of respiratory rate and sedation assessments every 1 h for the first 12 h, followed by every 2 h for 12–24 h after morphine administration. The guidelines also suggest considering other monitoring modalities as indicated, but data to support specific monitoring strategies has been limited.