# Chronic Pain in Pregnancy

## Introduction

Chronic pain affects approximately 20% of women of reproductive age, and managing it during pregnancy demands a careful balance between adequate maternal pain control and fetal safety. The physiological changes of pregnancy alter how drugs are absorbed, distributed, metabolized, and excreted. Many commonly used analgesics carry teratogenic risk, and untreated pain itself threatens both mother and fetus through mechanisms including preterm labor, preeclampsia, depression, and increased risk of substance use. Optimal outcomes depend on a multidisciplinary approach involving pain medicine, obstetrics, psychiatry, and physical therapy.

## Medication Safety in Pregnancy

### Regulatory Framework

The FDA retired the traditional category A/B/C/D/X pregnancy labeling system in 2015, replacing it with the Pregnancy and Lactation Labeling Rule (PLLR). Instead of a single letter grade, the PLLR requires narrative summaries of human data, animal data, and pharmacologic considerations for each medication. Clinicians should consult resources such as LactMed, Reprotox, and TERIS for the most current evidence, and any risk-benefit analysis must weigh both the risks of the medication and the risks of leaving pain untreated.

### Analgesic Safety Profiles

Acetaminophen remains the first-line systemic analgesic throughout pregnancy. Recent concerns about neurodevelopmental effects with prolonged high-dose exposure remain debated, and the current recommendation is to use it at the lowest effective dose for the shortest duration. Topical and locally infiltrated lidocaine is also considered safe because of minimal systemic absorption, and short courses of oral corticosteroids are acceptable for acute pain flares, though chronic use increases the risks of gestational diabetes and cleft palate.

Several medications require trimester-specific caution. NSAIDs are relatively safe in the first and second trimesters but are contraindicated after 32 weeks of gestation because they can cause premature closure of the ductus arteriosus, oligohydramnios, and neonatal renal impairment. Opioids may be used when benefits outweigh risks, but chronic use carries a high rate of neonatal opioid withdrawal syndrome (NOWS), affecting 55-94% of exposed neonates, and first-trimester codeine exposure has been associated with neural tube defects. Gabapentin has limited human data and animal studies showing skeletal and organ malformations, so it should be reserved for cases where no safer alternative exists. Pregabalin has demonstrated teratogenicity in animal models and is generally avoided.

Several medications are contraindicated outright. Valproic acid carries an absolute contraindication with a 10% risk of major malformations including neural tube defects. Topiramate is associated with cleft lip and palate and should not be used for migraine prophylaxis in pregnancy. Carbamazepine carries a 0.5-1% neural tube defect risk and should be avoided when alternatives exist. Paroxetine poses a first-trimester cardiac malformation risk and should be switched to sertraline if an SSRI is needed. High-dose aspirin is contraindicated, though low-dose aspirin (81 mg) may be used for preeclampsia prevention.

| Medication | First Trimester | Second Trimester | Third Trimester | Lactation |
|-----------|----------------|-----------------|----------------|-----------|
| Acetaminophen | Safe (lowest effective dose) | Safe | Safe | Safe |
| Ibuprofen/NSAIDs | Caution (use short course) | Acceptable (short course) | Contraindicated (>32 wks: ductus arteriosus closure) | Ibuprofen preferred; safe |
| Opioids | Caution (codeine: NTD risk) | Caution (NOWS risk with chronic use) | Caution (NOWS 55-94% with chronic use) | Short-course morphine acceptable |
| Gabapentin | Caution (limited human data) | Caution | Caution | Monitor infant for sedation |
| Pregabalin | Avoid (animal teratogenicity) | Avoid | Avoid | Insufficient data |
| Duloxetine | Caution (limited data) | Caution | Caution (neonatal withdrawal) | Low RID (~1%); generally acceptable |
| Valproic acid | Contraindicated (10% malformations) | Contraindicated | Contraindicated | Caution |
| Topiramate | Contraindicated (cleft lip/palate) | Contraindicated | Contraindicated | Caution |
| Topical lidocaine | Safe | Safe | Safe | Safe |
| Corticosteroids (oral) | Short course acceptable (cleft palate risk) | Short course acceptable | Short course acceptable | Compatible |

<image>Safety classification table for common pain medications across pregnancy trimesters, organized in a traffic-light format with green (generally safe: acetaminophen, topical lidocaine, physical therapy), yellow (caution with trimester-specific notes: NSAIDs safe T1-T2 but contraindicated T3, opioids with NOWS risk, gabapentin limited data), and red (contraindicated: valproic acid, topiramate, high-dose aspirin, carbamazepine), with a separate column showing lactation compatibility for each medication.</image>

## Physiological Changes Affecting Pain and Pharmacology

### Musculoskeletal Changes

Pregnancy alters the musculoskeletal system in ways that directly produce and exacerbate pain. Relaxin and progesterone increase ligamentous laxity, contributing to pelvic girdle pain, low back pain, and sacroiliac joint dysfunction. The anterior weight shift and progressive lordotic posture increase lumbar disc loading. Carpal tunnel syndrome affects 25-60% of pregnant women due to fluid retention, and diastasis recti with abdominal wall weakness alters core biomechanics.

### Pharmacokinetic Alterations

Pregnancy changes drug handling in virtually every compartment. Plasma volume increases by 40-50%, diluting drug concentrations and expanding the volume of distribution. Renal clearance increases by roughly 50% (reflected in a higher GFR), accelerating elimination of renally cleared drugs. Hepatic CYP3A4 and CYP2D6 activity increases, which may require upward dose adjustments for some medications. Albumin levels decrease, raising the free fraction of protein-bound drugs. The net effect is that some medications require higher doses to maintain therapeutic levels during pregnancy.

## Regional and Interventional Options

Ultrasound-guided peripheral nerve blocks avoid fluoroscopy and provide targeted analgesia without radiation exposure. Useful examples include occipital nerve blocks for headache and trigger point injections for myofascial pain. Sacroiliac joint injections can be performed under ultrasound guidance, and TENS (transcutaneous electrical nerve stimulation) is safe throughout pregnancy as long as electrodes are not placed over the uterus. Acupuncture has growing evidence for pregnancy-related low back pain and pelvic girdle pain and is generally safe when performed by trained practitioners.

Some approaches require modification. Epidural steroid injections may be considered in the second trimester for severe radiculopathy unresponsive to conservative measures, using ultrasound guidance to avoid fluoroscopy, and corticosteroid injections should be limited to the minimum effective dose and frequency.

Fluoroscopy and CT-guided procedures are contraindicated because of ionizing radiation exposure, particularly in the first trimester. Radiofrequency ablation lacks sufficient safety data in pregnancy. Intrathecal drug delivery system adjustments are complicated by pregnancy-related changes in CSF dynamics.

## Multidisciplinary Approach

### Physical Therapy

Physical therapy is the first-line treatment for pregnancy-related musculoskeletal pain. Prenatal exercise programs reduce low back pain incidence by 30-45%. Pelvic floor physical therapy addresses pelvic girdle pain and symphysis pubis dysfunction. Aquatic therapy provides weight-supported exercise with analgesic benefit. Supportive devices such as sacroiliac belts, maternity support garments, and ergonomic modifications complement active rehabilitation.

### Psychological Support

Pregnancy-adapted cognitive behavioral therapy helps with pain coping and anxiety management, and mindfulness-based interventions reduce pain catastrophizing while improving maternal well-being. Screening for perinatal depression and anxiety is important because these conditions amplify pain perception. Clinicians should proactively address fears about labor pain, medication safety, and the challenges of parenting with chronic pain.

### Obstetric Coordination

A birth plan should be developed that addresses analgesic preferences and contingencies. Patients on chronic opioids need early anesthesia consultation because cross-tolerance affects both neuraxial and systemic analgesia. Planning for intrapartum pain management, including epidural timing and dosing, should begin well before delivery. When NOWS risk is present, neonatology should be notified in advance.

<image>Illustration of a multidisciplinary care model for chronic pain in pregnancy showing a pregnant patient at center with connections to six specialties: pain medicine (medication management, interventional options), obstetrics (prenatal monitoring, birth planning), physical therapy (prenatal exercises, pelvic floor rehabilitation, aquatic therapy), psychology (CBT, mindfulness, perinatal mood screening), anesthesiology (labor analgesia planning, opioid-tolerant protocols), and neonatology (NOWS preparation and monitoring), with a timeline bar below showing care priorities across first, second, and third trimesters and postpartum period.</image>

## Postpartum Pain Transition

### Acute Postpartum Pain Management

After vaginal delivery, acetaminophen and ibuprofen are first-line, with short-course opioids reserved for severe perineal tears. After cesarean delivery, multimodal analgesia is standard: neuraxial morphine, scheduled acetaminophen and NSAIDs, with opioids for breakthrough pain. TAP blocks and wound infiltration reduce opioid requirements post-cesarean section. Persistent postsurgical pain after cesarean delivery occurs in 10-15% of cases.

### Transitioning Chronic Pain Medications

Medications held during pregnancy can often be restarted within 24-48 hours postpartum if the patient is not breastfeeding. For breastfeeding mothers, restart timing must account for infant exposure through breast milk. Postpartum hormonal shifts may trigger pain flares that require proactive management, and the sleep deprivation and increased physical demands of newborn care reliably exacerbate chronic pain.

### Postpartum Depression and Pain

Chronic pain increases postpartum depression risk by 2-3 fold. This relationship is bidirectional: pain and depression share neurobiological pathways involving serotonin and norepinephrine. The Edinburgh Postnatal Depression Scale should be administered at postpartum visits. Duloxetine is a useful option because it addresses both pain and depression and is considered moderately safe during lactation.

## Breastfeeding-Compatible Analgesics

Several analgesics are generally compatible with breastfeeding. Acetaminophen has minimal breast milk transfer and is safe at standard doses. Ibuprofen has very low milk transfer (less than 1% of maternal dose) and is the preferred NSAID during lactation. Low-dose opioids such as morphine and hydromorphone appear in small amounts in breast milk, and short courses are acceptable with infant monitoring. Topical and local lidocaine produces negligible milk levels, and nortriptyline has low milk transfer, making it the preferred tricyclic antidepressant during lactation.

Some medications require caution. Gabapentin is present in breast milk, so the infant should be monitored for sedation and poor feeding. Duloxetine has a low relative infant dose of about 1% and is generally considered acceptable. Naproxen has a longer half-life than ibuprofen and is less preferred but acceptable for short courses.

Several medications should be avoided during breastfeeding. Codeine carries an FDA warning due to the risk that CYP2D6 ultra-rapid metabolizers may produce toxic morphine levels in breast milk, potentially causing infant sedation and death. Meperidine has an active metabolite that accumulates in neonates. High-dose aspirin carries a risk of Reye syndrome (though low-dose is acceptable). Ergotamine suppresses lactation and causes infant toxicity.

<image>Decision flowchart for analgesic selection during breastfeeding, starting with pain severity assessment (mild, moderate, severe), then branching through first-line options (acetaminophen, ibuprofen), second-line options (nortriptyline for neuropathic, gabapentin with monitoring, short-course morphine), and contraindicated medications (codeine, meperidine, aspirin), with each branch showing relative infant dose percentages, key monitoring parameters for the infant (sedation, feeding, weight gain), and LactMed reference codes.</image>

## Clinical Pearls

Acetaminophen remains the first-line systemic analgesic throughout pregnancy and lactation, used at the lowest effective dose for the shortest necessary duration. NSAIDs are contraindicated after 32 weeks of gestation due to premature ductus arteriosus closure -- a high-yield board topic. Chronic opioid use in pregnancy requires neonatology involvement for NOWS monitoring, and opioids should never be abruptly discontinued because withdrawal can cause preterm labor and fetal distress. Ultrasound-guided interventional procedures allow safe regional analgesia without radiation exposure during pregnancy. Physical therapy is the cornerstone of pregnancy-related pain management and should be initiated early in pregnancy for prevention.

## References

1. Babb M, Koren G, Einarson A. Treating pain during pregnancy. *Canadian Family Physician*. 2010;56(1):25-27.
2. Ray-Griffith SL, Wendel MP, Stowe ZN, Magann EF. Chronic pain during pregnancy: a review of the literature. *International Journal of Women's Health*. 2018;10:153-164.
3. Sachs HC, Committee on Drugs. The transfer of drugs and therapeutics into human breast milk: an update on selected topics. *Pediatrics*. 2013;132(3):e598-e623.
4. Oliveira C, Lotto CR, Oliver A, et al. Peripartum pain management for women on opioid agonist therapy: a comprehensive review. *Pain Medicine*. 2022;23(Suppl 1):S31-S46.