Yes, Postnasal Drip Can Trigger the Cough Reflex in Pregnancy
Postnasal drip (now termed Upper Airway Cough Syndrome or UACS) can absolutely trigger the cough reflex through mechanical stimulation of cough receptors in the hypopharynx and larynx, and this mechanism is particularly relevant in a pregnant woman with an upper respiratory tract infection. 1
Mechanism of Cough Induction
The pathophysiology involves two primary mechanisms:
Mechanical stimulation: Secretions from the nose and sinuses drip down and directly stimulate cough receptors located in the hypopharynx or larynx, activating the afferent limb of the cough reflex. 1
Heightened cough reflex sensitivity: Upper airway inflammation can sensitize the cough reflex, lowering the threshold for cough initiation even with minimal stimulation. 1 This means the cough receptors in the upper airway become hyperresponsive during upper respiratory infections. 1
Pharyngeal stimulation: Fluid infusion into the pharynx or mechanical stimulation with postnasal drip can evoke vigorous coughing through vagal, glossopharyngeal, or trigeminal nerve pathways. 1
Clinical Context in Pregnancy
For your 5-month pregnant patient with URTI:
UACS is the most common cause of both acute and chronic cough, particularly in the setting of upper respiratory infections like the common cold. 1 Since URTIs are extremely common, UACS represents the most frequent etiology of acute cough. 1
Pregnancy rhinitis complicates the picture: Approximately 20% of pregnant women develop pregnancy rhinitis (nasal congestion in the last 6+ weeks of pregnancy without infection or allergy), which can coexist with or mimic URTI symptoms. 2, 3 However, at 5 months gestation, true pregnancy rhinitis is less likely to be the primary cause.
"Silent" postnasal drip occurs: Approximately 20% of patients with UACS-induced cough are unaware of postnasal drainage or its connection to their cough. 1 The absence of subjective postnasal drip sensation does not rule out UACS.
Diagnostic Approach
Look for these specific clinical features:
Symptoms: Sensation of throat drainage, frequent throat clearing, throat tickle, nasal congestion, nasal discharge, or hoarseness. 1 Many patients will report at least one of these, but some may not. 1
Physical examination findings: Mucoid or mucopurulent secretions in the posterior pharynx or oropharynx, cobblestone appearance of oropharyngeal mucosa. 1 These findings are sensitive but not specific. 1
Critical caveat: There is no objective test to prove postnasal drip is causing cough. 1 The diagnosis is clinical and ultimately confirmed by response to empiric therapy. 1
Treatment Recommendations for Pregnancy
The diagnosis is confirmed by therapeutic response, making empiric treatment both diagnostic and therapeutic. 1
For symptomatic management in pregnancy:
First-line: Nasal saline irrigation/washings are safe and can provide relief without medication exposure. 2, 3 This should be the initial approach given pregnancy.
Analgesics/antipyretics: Acetaminophen or ibuprofen (ibuprofen only in second trimester, avoid in third trimester) for associated pain, fever, and inflammation. 4
Oral decongestants: May provide symptomatic relief if no contraindications (hypertension, preeclampsia risk). 4 Use cautiously in pregnancy.
Topical nasal decongestants: Can provide good temporary relief but should be limited to 3-5 days maximum to avoid rebound congestion (rhinitis medicamentosa). 4, 2, 3 Pregnant women tend to overuse these due to the relief they provide. 2, 3
Nasal corticosteroids: Not proven effective for pregnancy rhinitis specifically, but may be used when indicated for other rhinitis types. 2, 3 Systemic corticosteroids should be avoided. 3
Cough suppressants: Dextromethorphan can be prescribed for dry, bothersome cough. 4 Codeine is generally avoided in pregnancy.
Important Clinical Pitfalls
Do not assume discolored nasal discharge means bacterial sinusitis: Discolored discharge indicates inflammation, not necessarily bacterial infection. 4 Antibiotics are not indicated for viral URTI. 4
Distinguish from true bacterial sinusitis: If symptoms persist beyond 3 weeks, fever exceeds 4 days, or clinical deterioration occurs, consider bacterial sinusitis requiring antibiotics. 4
Monitor for medication overuse: Pregnant patients may overuse topical decongestants due to effective relief, creating rhinitis medicamentosa on top of their original condition. 2, 3
Alternative mechanism consideration: Recent evidence suggests that upper airway inflammation may cause cough through direct irritation and sensitization of cough receptors rather than solely through mechanical postnasal drip. 1, 5 The American College of Chest Physicians now recommends the term "Upper Airway Cough Syndrome" instead of "postnasal drip syndrome" to reflect this uncertainty. 1