What is the best laxative for a woman in her third trimester of pregnancy?

Best Laxative in Third Trimester Pregnancy

Polyethylene glycol (PEG) is the best laxative for third trimester pregnancy, with lactulose as an equally safe alternative, though PEG causes less bloating. 1, 2, 3

First-Line Treatment Approach

Dietary Modifications (Initial Step)

• Increase dietary fiber to approximately 30 g/day through fruits, vegetables, whole grains, and legumes 1, 2, 4
• Ensure adequate fluid intake, particularly water, to soften stools and improve transit time 1, 2, 3
• These measures alone resolve constipation in many pregnant women but are often insufficient 5, 6

Bulk-Forming Agents (If Dietary Changes Fail)

• Psyllium husk or methylcellulose are safe due to minimal systemic absorption 1, 2, 3
• These agents improve stool viscosity and transit time while increasing bulk 4
• Caution: Excessive fiber can cause maternal bloating 4

Pharmacologic Treatment (Preferred Options)

Osmotic Laxatives (Most Effective First-Line Pharmacotherapy)

Polyethylene glycol (PEG) 17g daily is the preferred osmotic laxative because:

• It can be safely administered throughout pregnancy with minimal systemic absorption 1, 2, 3
• It has faster onset of bowel action compared to lactulose 7
• It causes fewer flatulences than lactulose 7
• It is recommended by the American Gastroenterological Association as a safe treatment option 1, 3

Lactulose is an equally safe alternative:

• It is the only osmotic agent specifically studied in pregnancy 3
• It may cause more bloating than PEG 1, 2, 3
• Recommended dose allows for flexible titration based on response 7

Second-Line Options (Use With Caution)

Stimulant Laxatives

• Should generally be avoided as routine therapy but can be used cautiously for short-term relief when other methods fail 1, 2, 4
• Bisacodyl and sodium picosulfate can be considered in the second and third trimester if first-line treatments fail 7
• Important caveat: Stimulant laxatives are more effective than bulk-forming agents but may cause more side effects, including tenesmus which could theoretically trigger preterm labor 5, 8
• Senna has evidence supporting its use but should be limited to short-term use 5, 8

Clinical Considerations Specific to Third Trimester

Assessment Requirements

• Evaluate frequency and consistency of bowel movements 2, 4
• Screen for pain or bleeding during defecation 2, 4
• Screen for hemorrhoids, which occur in approximately 80% of pregnant women 4, 3

Hemorrhoid Management (Common Comorbidity)

• Hydrocortisone foam has been shown to be safe in the third trimester for symptomatic relief 2
• Stool softeners (PEG) help achieve softer stools and reduce strain on hemorrhoids 2

Critical Pitfalls to Avoid

• Do not prescribe newer secretagogues (linaclotide, plecanatide, lubiprostone) during pregnancy due to insufficient safety data 3
• Do not use osmotic and stimulant laxatives long-term to avoid dehydration or electrolyte imbalances 6
• Do not withhold treatment, as constipation affects 20-40% of pregnant women and significantly impacts quality of life 2, 4, 3

Why These Recommendations

The American Gastroenterological Association's 2024 guidelines specifically recommend dietary fiber, lactulose, and polyethylene glycol-based laxatives as safe treatment options for constipation in pregnancy 1. PEG and lactulose have minimal systemic absorption, making them the safest pharmacological options 2, 3. The evidence base for PEG is robust despite lactulose being the only osmotic agent specifically studied in pregnancy, and PEG's superior tolerability profile (less bloating, faster onset) makes it the preferred choice 3, 7.