Constipation in Early Pregnancy: Causes and Treatment
Direct Answer
For constipation in early pregnancy, start with dietary fiber increased to 30 g/day, then escalate to polyethylene glycol (PEG) 17g daily as first-line pharmacologic therapy if dietary measures fail. 1, 2
Underlying Causes
Constipation affects 20-40% of pregnant women and results from multiple mechanisms: 1, 2
- Hormonal changes: Elevated progesterone levels slow gastrointestinal motility throughout pregnancy 1, 2
- Medication effects: Iron supplementation and prenatal vitamins commonly contribute 1
- Anatomic factors: The gravid uterus compresses the rectum, particularly in later trimesters 1
- Dietary insufficiency: Most pregnant women in the United States consume inadequate dietary fiber 1
Treatment Algorithm
Step 1: Non-Pharmacologic Measures (First-Line)
Increase dietary fiber intake to approximately 30 g/day through fruits, vegetables, whole grains, and legumes. 1, 2 This addresses the primary dietary deficiency and promotes regular bowel movements without systemic absorption. 1
Ensure adequate fluid intake, particularly water, to soften stools and improve transit time. 1, 2 Hydration works synergistically with fiber to ease bowel movements. 1
Step 2: Bulk-Forming Agents (If Dietary Changes Insufficient)
Use psyllium husk or methylcellulose as safe bulk-forming agents. 1, 2 These agents have minimal systemic absorption and are not expected to cause congenital anomalies. 2, 3 Soluble fiber like psyllium improves both stool viscosity and transit time compared to insoluble fiber. 1
Step 3: Osmotic Laxatives (Preferred Pharmacologic Option)
Polyethylene glycol (PEG) 17g daily is the preferred osmotic laxative during pregnancy. 1, 2 PEG has minimal systemic absorption, making it safe throughout pregnancy. 2 It offers faster onset of action and causes less bloating than lactulose. 4
Lactulose is an alternative osmotic laxative but may cause more maternal bloating. 1, 2 While safe due to lack of absorption in the small intestine and absence in breast milk, 5 it produces more gas-related side effects than PEG. 1, 4
Step 4: Stimulant Laxatives (Short-Term Use Only)
Stimulant laxatives should generally be avoided as routine therapy but can be used cautiously for short-term relief when other methods fail. 2 Safety data on these medications are conflicting. 1 If used in the second or third trimester, bisacodyl and sodium picosulfate are options, 4 though they carry risk of abdominal discomfort (RR 2.33) and diarrhea (RR 4.50) compared to bulk-forming agents. 6
Clinical Assessment
Before initiating treatment, evaluate: 1, 2
- Frequency and consistency of bowel movements to establish baseline severity 1, 2
- Presence of pain or bleeding during defecation to identify complications like hemorrhoids 1, 2
- Severity of symptoms to guide treatment intensity 1
Screen for hemorrhoids, which occur in approximately 80% of pregnant women, more commonly in the third trimester. 1 Hydrocortisone foam is safe in the third trimester for symptomatic relief. 2
Important Caveats
Excessive fiber and osmotic laxatives like lactulose can cause maternal bloating, 1 which may reduce compliance. Start with lower doses and titrate upward.
Osmotic and stimulant laxatives should be used only short-term or occasionally to avoid dehydration or electrolyte imbalances. 3 Prolonged use requires monitoring.
Most laxatives carry pregnancy category B or C classification, 7 reflecting limited human data rather than proven harm. The lack of systemic absorption with bulk-forming agents and osmotic laxatives provides reassurance. 2, 3
Evidence Quality
The 2024 AGA guidelines 1 and 2025 Praxis Medical Insights summary 2 provide the strongest and most recent recommendations, both emphasizing the step-up approach from dietary modification to PEG. A 2015 Cochrane review 6 found insufficient high-quality evidence comparing interventions, with only moderate-quality data showing stimulant laxatives improve constipation more than bulk-forming agents but with more side effects. The recommendation for PEG over lactulose is supported by comparative studies showing better tolerability. 4