Abdominal pain can be a worrisome symptom heralding a miscarriage, especially if it is accompanied by vaginal bleeding and thus should result in prompt evaluation by an obstetrician. Other causes of abdominal pain result from rapid stretching and hematoma formation of the round ligament resulting in pain and tenderness that radiates to the pubic tubercle. Rapid stretching of the rectus abdominal muscle can result in a hematoma within the rectus sheath that produces abdominal wall pain that is exacerbated with flexion of the abdominal muscles. Both conditions are treated with localized heat and, if severe, oral analgesics which we will discuss the safety of later in the chapter.¹

Low back pain is one of the most common complaints from pregnant women and is caused by a combination of weight gain, predominantly in the abdominal region, and an increase in pregnancy hormones such as relaxin, progesterone, and estrogen, which contribute to joint laxity. The increased weight causes increased axial loading, pelvic tilt with resultant hyperlordosis, and stretching and weakening of abdominal muscles, which can all culminate to cause back and pelvic girdle pain. The incidence increases with increasing gestational age and by 35 weeks, the prevalence of low back pain and pelvic girdle pain reach up to 71.3% and 64.7%, respectively.⁴ See Table 26.1 for a summary of the different characteristics of low back pain vs pelvic girdle pain.

While back and pelvic girdle pain are common during pregnancy, it is important to first rule out any red flag symptoms such as bowel or bladder incontinence, radiculopathy, or weakness prior to forming a treatment plan. If the patient has red flag symptoms such as neurologic deficits, then imaging with magnetic resonance imaging (MRI) is warranted. Assuming none of these symptoms are present, it is reasonable to start with conservative therapy such as yoga, water exercises, acupuncture, or physical therapy. Oral analgesics can be used and are discussed in more detail below. Transcutaneous electrical nerve stimulation (TENS) was found to be equivalent to oral acetaminophen or exercise at treating back pain in pregnancy in one randomized controlled trial.⁵

Acetaminophen is an antipyretic analgesic that does not share the anti-inflammatory properties of nonsteroidal anti-inflammatory drug (NSAID) and does not affect prostaglandin synthesis. For persistent pain during pregnancy that cannot be controlled with conservative measures such as yoga, acupuncture, or physical therapy, acetaminophen is an acceptable first-line oral analgesic agent in pregnancy as it has no known teratogenic effects and does not cause fetal ductus arteriosis closure in the third trimester.¹

Opioids can be used for short-term relief of acute pain especially following nonobstetric surgery in pregnant women. Morphine, fentanyl, and hydromorphone are all acceptable options for acute pain control when potent parenteral analgesia is necessary for surgical procedures. Post-operatively, a short course of oral analgesics such as oxycodone or hydrocodone combined with acetaminophen are reasonable options to treat pain associated with surgical
procedures.¹ Neonatal abstinence syndrome, characterized by difficulty feeding, regulating temperature, as well as respiratory distress and seizures, is a feared complication of chronic opioid use in pregnancy. For this reason, opioids should not be used for prolonged periods during pregnancy if it can be avoided.⁷ Patients who have a chronic pain syndrome requiring chronic opioids or have a substance abuse disorder and take methadone fall under the category of chronic pain and will not be discussed in this chapter. Neuraxial administration of hydrophilic opioids such as morphine greatly reduces postoperative opioid consumption when given for cesarean section.¹

Nonsteroidal anti-inflammatory drugs (NSAIDs) are a class of medications that cause antiinflammatory and analgesic properties and are commonly prescribed for musculoskeletal pain; however, caution must be exercised when considering this medication in the parturient. Examples include ibuprofen, naproxen, indomethacin, and ketorolac, the former two of which are available over the counter (OTC).¹ This class of medications poses different risks to the unborn fetus at different gestational ages. The risk of use for short durations in the first trimester appears low but cannot be excluded. The FDA recommends against use of NSAIDs after 20 weeks of gestational age owing to a small but serious risk of renal insufficiency of the fetus and subsequent oligohydramnios. This condition is usually reversed with discontinuation of the medication. It is also recommended to avoid NSAIDs (excluding 81 mg aspirin) after 30 weeks of gestation due to the increased risk of premature closure of the fetal ductus arteriosis.⁸

Ergotamine is an effective treatment for migraine headaches but is contraindicated in pregnancy due to its teratogenicity and ability to cause uterine contractions and spontaneous abortion in high doses. Methylergonovine is an ergot alkaloid given to the parturient for treatment of uterine atony.¹

The first stage of labor is visceral in nature and starts at the onset of labor and extends to full cervical dilation which is considered to be 10 cm. Uterine contraction and resultant myometrial ischemia causes release of leukotrienes, histamine, serotonin, substance P, and bradykinins which stimulate chemoreceptors. This visceral type of pain is transmitted pain via small unmyelinated “C” fibers, which travel with sympathetic fibers and pass through the uterine, cervical, and hypogastric nerve plexuses into the lumbar sympathetic chain. The pain fibers from the sympathetic chain enter the white rami communicantes at the T10-L1 spinal nerves and pass through the posterior nerve roots and synapse in the dorsal horn of the spinal cord.⁹

The second stage of labor begins with complete cervical dilation and ends with delivery of the fetus. Somatic nerve fibers are responsible for carrying pain signals during the second stage of labor. The transition from the first to second stage of labor involving both somatic and visceral components is reported to cause an increase in pain intensity. Distention of vaginal and perineal tissues causes pain signals to be transmitted to the spinal cord at the level of S2, S3, and S4, primarily via the pudendal nerve. Other nerves involved in signaling pain from the
perineum include the ilioinguinal nerve and the genital branch of the genitofemoral nerve. As the fetus descends through the pelvic outlet, rectal pressure gives the parturient the urge to valsalva and push to expel the fetus.¹⁰

While many young healthy women can tolerate the pain associated with labor and may choose to forgo any pain intervention, pain itself is not necessarily benign. Severe pain such as that present during labor causes neurohumoral, respiratory, and psychological consequences. Intermittent hyperventilation associated with labor can cause hypocarbia, which inhibits ventilatory drive causing maternal and fetal hypoxemia. Hyperventilation can also result in a respiratory alkalosis, which causes a left shift of the oxyhemoglobin curve, and increases the affinity for oxygen of maternal hemoglobin, while decreasing oxygen delivery to the fetus. Epidural analgesia reduces pain and allows the patient to maintain regular respirations resulting in increased oxygen tension for mother and fetus.¹¹ Elevated plasma catecholamines can decrease uteroplacental perfusion by increasing maternal peripheral vascular resistance. Small primate studies reflected that stress and pain cause fetal acidosis by lowering fetal oxygenation and can also slow fetal heart rate.¹² The psychological consequences of enduring such a traumatic and painful event can contribute to the development of postpartum depression and even posttraumatic stress disorder. One study involving 1288 women having either vaginal or cesarean delivery reported that persistent pain and postpartum depression was related to the severity of acute pain after childbirth and was not related to the type (vaginal vs cesarean) of delivery.¹³

Preparation for the childbirth can significantly modify the pain experience and help laboring mothers cope with the pain. The Lamaze method after Dr. Ferdinand Lamaze focuses on breathing techniques and conscious relaxation to decrease pain perception.¹⁴ Preparation reduces the fear and anxiety, which can exacerbate pain. The continuous presence of a support person, such as a doula or midwife, has been shown to reduce pain severity.¹