What medications should be initiated at 20 weeks gestation in a pregnant patient?

Medications to Initiate at 20 Weeks Gestation (5 Months Pregnancy)

At 20 weeks gestation, all pregnant women should be taking a prenatal multivitamin containing folic acid (0.4-1.0 mg), iron (30-60 mg elemental iron), and calcium supplementation (1200 mg daily if dietary intake is low), while women at high risk for preeclampsia should already be on low-dose aspirin (100-150 mg daily) started before 16 weeks. 1

Universal Supplementation for All Pregnant Women

Folic Acid

• Continue folic acid supplementation at 0.4-1.0 mg daily throughout pregnancy in a multivitamin formulation 2, 3
• Women should have started this preconceptionally, but if not already taking it, initiate immediately 2
• Higher doses (4-5 mg) are only needed for women with prior neural tube defects or specific high-risk conditions 2

Iron Supplementation

• Initiate or continue elemental iron 30-60 mg daily for all pregnant women 1, 3, 4
• Iron can be taken with one of the calcium doses (morning or evening) despite theoretical absorption interactions, as the benefit of adherence outweighs minor absorption concerns 1
• Intermittent dosing may reduce gastrointestinal side effects while maintaining efficacy 3

Calcium Supplementation

• Start calcium 1200 mg elemental calcium daily if dietary intake is low (<600-800 mg/day) 1
• The WHO recommends initiating calcium at 20 weeks gestation specifically for preeclampsia prevention 1
• Divide into 3 daily doses of 500 mg each to optimize absorption 1
• This is particularly important in low-income populations with inadequate dietary calcium 1

Risk-Stratified Aspirin Prophylaxis

High-Risk Women (Should Already Be Taking)

Women with major risk factors should have started low-dose aspirin 100-150 mg daily before 16 weeks gestation (ideally by 12 weeks), continuing until 36-37 weeks 1, 5, 6

Major risk factors include: 1, 5

• Prior preeclampsia
• Chronic hypertension
• Pregestational diabetes mellitus
• Maternal BMI >30
• Chronic kidney disease
• Antiphospholipid syndrome

If not yet started by 20 weeks in high-risk women, initiate immediately as late initiation still provides benefit 1

Moderate-Risk Women

Women with ≥2 minor risk factors (advanced maternal age, family history of preeclampsia, primiparity, connective tissue disorders) should also receive aspirin prophylaxis 1

Antihypertensive Medications (If Indicated)

For Chronic Hypertension

Maintain blood pressure at 110-140/80-85 mmHg using pregnancy-compatible antihypertensives 1

Acceptable first-line agents: 1

• Labetalol
• Methyldopa
• Nifedipine (long-acting)
• Diltiazem

Absolutely contraindicated medications that must be stopped: 1, 5, 7

• ACE inhibitors (cause fetal renal dysgenesis)
• Angiotensin receptor blockers
• Direct renin inhibitors
• Atenolol (associated with fetal growth restriction)
• Statins

Additional Considerations for Specific Conditions

Women with Autoimmune/Rheumatic Disease

Pregnancy-compatible immunosuppressants can be continued: 1

• Hydroxychloroquine (up to standard doses)
• Azathioprine (up to 2 mg/kg/day)
• Sulfasalazine (up to 2 g/day with mandatory folic acid supplementation)
• Tacrolimus and cyclosporine (at lowest effective doses)
• Colchicine (1-2 mg/day)

NSAIDs must be discontinued after 28 weeks gestation due to risks of oligohydramnios and premature ductus arteriosus closure 1

Women with Diabetes

Low-dose aspirin 100-162 mg daily should be initiated at 12-16 weeks to reduce preeclampsia risk 1

Critical Timing and Practical Implementation

Why 20 Weeks Matters

• The WHO specifically recommends calcium initiation at 20 weeks based on meta-analysis data, though earlier initiation is acceptable and may be more practical 1
• This timing aligns with routine mid-pregnancy ultrasound and antenatal visits 1
• Many women in resource-limited settings present for first antenatal care around this time 1

Adherence Strategies

Simplify the regimen by coordinating timing: 1

• Take iron and calcium together (despite theoretical interactions) to reduce complexity
• Use combined prenatal multivitamin formulations when possible
• Counsel that calcium and iron can be taken at the same time of day

Common Pitfalls to Avoid

• Do not delay calcium supplementation if women present after 20 weeks—still initiate as benefit persists 1
• Do not separate calcium and iron dosing into 4+ daily administrations, as this reduces adherence more than it improves absorption 1
• Do not use high-dose vitamin A (>3000 IU/day retinol) due to teratogenic risk 3, 8
• Do not combine IV magnesium sulfate with calcium channel blockers if treating hypertension, due to myocardial depression risk 5, 7