For how many days should oral progesterone (Susten) be continued in a woman at 10 weeks and 4 days gestation who has had a brief episode of first‑trimester bleeding?

Duration of Progesterone (Susten) for First-Trimester Bleeding at 10 Weeks 4 Days

Continue progesterone until 12 completed weeks of gestation, not 16 weeks, because the beneficial effect is complete by 12 weeks when the placenta assumes progesterone production, and prolonging treatment beyond this point exposes the fetus to unnecessary pharmaceutical progesterone without additional benefit. 1

Evidence-Based Duration

• The major clinical trial (PRISM) that established progesterone's role in early pregnancy bleeding showed no benefit from starting progesterone after 9 weeks gestation, and the full protective effect was present by 12 weeks of pregnancy. 1

• At 12 weeks gestation, the placenta—not the maternal ovary—becomes the primary source of progesterone production, making exogenous supplementation physiologically unnecessary beyond this point. 1

• Although NICE guidelines recommend continuing until 16 weeks, this duration is not evidence-based and may expose the offspring to theoretical long-term health risks from prolonged pharmaceutical progesterone exposure. 1

Practical Recommendation for Your Patient

Since your patient is already at 10 weeks 4 days:

• Continue progesterone for approximately 10 more days (until 12 completed weeks of gestation). 1

• Use vaginal micronized progesterone 400 mg twice daily (total 800 mg/day) if she has a history of previous miscarriage(s). 2

• If no history of recurrent miscarriage exists, the evidence for progesterone benefit is weaker—the PRISM trial showed no significant difference in live births ≥34 weeks between progesterone and placebo groups overall (75% vs 72%, P=0.08). 3

Important Caveats

• Do not confuse formulations: Injectable 17-hydroxyprogesterone caproate (17P) is used for preterm birth prevention starting at 16-20 weeks in women with prior spontaneous preterm birth—this is a completely different indication and should not be used for first-trimester bleeding. 2

• Progesterone has no proven benefit in multiple gestations, active preterm labor, or preterm premature rupture of membranes. 4, 2

• The strongest evidence for progesterone benefit exists in women with both bleeding AND a history of previous miscarriage—if your patient lacks this history, shared decision-making about continuing treatment is appropriate. 2, 3