Obesity and pregnancy

women who meet the BMI criteria for obesity (BMI > 30 kg/m2) pre-pregnancy will maintain that status in pregnancy

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

Ante-partum & peri-partum

The comorbid conditions associated with obesity before and during pregnancy include

gestational diabetes mellitus (GDM),
hypertensive disorders of pregnancy (HDP),
psychiatric diagnoses including depression and anxiety,
preterm birth,
labor complications,
- need for labour induction
- augmentation w/ Oxytocin
- failure to progress labour
- assisted vaginal delivery
- shoulder dystocia (BMI ≥ 35)
  - ? ∵ ↑ post-term birth
unscheduled CS

Fetal implication:

neural tube defect
cardiac defects
macrosomia (birth weight >4000g) / LGA (BW >90% percentile)
difficult TAS to detect anomalies

Post-partum

? ↑ PPH (inconclusive evidence)
Risk factors:

↑ Vd for Uterotonics,
challenges in performing thorough fundal and bimanual exams,
↑ uterine size ∵ post-term deliveries & LGA fetuses

Surgical-site infections (SSI) post-cesarean delivery occur twice as frequently for obese women compared to normal BMI parturients

ACOG recommends that patients receive a first-generation cephalosporin w/i 60 minutes prior to skin incision for the prevention of SSI with a standard 2-gram 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 grams 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

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/m2 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 (> 22kg) and cesarean delivery increased the risk of VTE independently, and their combined effect amplified the risk.

Neuraxial techniques

Obesity is a known risk factor for operative delivery. Neuraxial anesthesia is a priority among obese parturients due to the increased risk of difficult airway

↑ Risk of

accidental dural puncture
- but ↑ BMI may be protective to PDPH after ADP?
epidural failure
once PDPH did occur in obese patients, there were no reported differences in headache severity or the need for epidural blood patch compared to lower BMI patients.

In general, an epidural catheter should be placed early in labor to avoid time pressure and maximize patient collaboration

DPE with a 26-gauge spinal needle did not replicate the results seen with 25-gauge needles

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

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.

A 17g epidural needle is often the most suitable 'introducer' to guide the spinal needle in the correct direction

Resp

obesity is often co-morbid with preeclampsia, which is its own risk factor for airway edema, worsening airway obstruction, and difficult airway likely due to edema of the face, neck and airway

Increased rates of OSA are seen among parturients with a BMI > 30 kg/m2, and OSA rates increase with increasing BMI

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 dose
- 0.05 mg – 0.15 mg intrathecal
- 1 – 3 mg epidural morphine
ultra-low doses
- < 0.05 mg intrathecal
- < 1 mg epidural morphine

Guidelines promote the use of low- or ultra-low doses neuraxial morphine in obese women (BMI > 40 kg/m2) 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 one hour for the first twelve hours, followed by every two hours for 12 to 24 hours after morphine administration.

References

Morbid Obesity Optimizing Neuraxial Analgesia and Cesarean Delivery Outcomes - BPRCA