Venous Thromboembolism and Hormonal Contraception

clinicians to the FSRH Combined Hormonal Contraception guideline for current practice, and to the UK Medical Eligibility Criteria for Contraceptive Use (UKMEC) for risk categorisation) Successor guidance: FSRH CHC guideline (last full update 2019, amended October 2023) and UKMEC (2016, with periodic amendments; 2025 edition now in circulation).

Background

RCOG withdrew GTG 40 and now signposts clinicians to the Faculty of Sexual and Reproductive Healthcare (FSRH) for VTE risk assessment in contraception. The underlying pharmacology and risk-stratification the original guideline established — that risk varies by route (oral vs transdermal/vaginal vs none), by progestogen type in combined methods, and is materially lower for progestogen-only methods — remains the standard teaching point and has been carried forward into FSRH/UKMEC guidance largely unchanged.

VTE Risk by Method (MHRA/EMA 2013 pharmacovigilance review figures, adopted by FSRH)

These are the reference figures cited in UK regulatory and FSRH guidance (approximate incidence per 10,000 woman-years):

• Baseline (non-pregnant, not using combined hormonal contraception, CHC): ~2 per 10,000 woman-years
• CHC containing levonorgestrel, norgestimate, or norethisterone (second-generation-type progestogens): 5–7 per 10,000 woman-years
• CHC containing etonogestrel or norelgestromin (vaginal ring, patch): 6–12 per 10,000 woman-years
• CHC containing gestodene, desogestrel, or drospirenone (third/fourth-generation-type progestogens): 9–12 per 10,000 woman-years — the highest-risk group among combined methods
• Pregnancy: substantially higher than any CHC method (commonly cited as roughly 29 per 10,000 woman-years, with postpartum risk higher still in the first weeks) — used clinically to counter the misconception that stopping contraception "for safety" during a pregnancy attempt or workup is risk-free

All combined methods (pill, patch, ring) share the same estrogen-driven mechanism regardless of route, because none of the licensed CHC routes avoids the estrogen's systemic effect on hepatic clotting-factor synthesis in the way transdermal HRT does for estrogen-only therapy.

Progestogen-only and LARC methods

• Progestogen-only pill (POP): evidence does not show an increased VTE risk versus non-users — UKMEC generally categorises POP as Category 1 (or 2 in a woman with an existing VTE) precisely because it lacks the estrogen component driving CHC-associated risk.
• LNG-IUS and etonogestrel implant: not associated with a clinically significant increase in VTE risk; typically UKMEC Category 1–2 even in women with risk factors, and are preferred methods for women with a history of VTE or on anticoagulation.
• Progestogen-only injectable (DMPA): some observational data suggest a small possible increase in risk relative to other progestogen-only methods, which is why FSRH/UKMEC treat it slightly more cautiously than the POP or LNG-IUS in women with additional VTE risk factors — check the current UKMEC summary table rather than assuming parity with other progestogen-only methods.
• Current or past VTE (especially on anticoagulation) is UKMEC Category 4 for CHC (unacceptable risk) but only Category 2 for most progestogen-only methods — this contrast is a recurrent exam point.

Risk Factor Assessment Before Prescribing CHC

• Take a personal and family history of VTE before initiating or continuing CHC.
• Key independent risk factors: obesity (BMI ≥30, and especially ≥35), immobility, major/planned surgery, smoking, age >35, known thrombophilia, and a first-degree relative with unprovoked VTE under age 45.
• Risk factors are additive — reassess UKMEC eligibility at intervals, not just at first prescription, since BMI, smoking status, and mobility change over time.
• CHC should not be started, or should be stopped and switched to a progestogen-only or non-hormonal method, when a new VTE risk factor emerges (e.g. a planned major operation, a new thrombophilia diagnosis).

High-Yield Exam Points

• Baseline VTE risk in non-pregnant non-users ≈ 2/10,000 woman-years; CHC with levonorgestrel/norgestimate/norethisterone ≈ 5–7/10,000; CHC with desogestrel/gestodene/drospirenone ≈ 9–12/10,000 — the highest-risk progestogen group among combined methods.
• Pregnancy carries a substantially higher VTE risk than any CHC method — do not withhold or interrupt contraception "to reduce VTE risk" when the realistic alternative is an unintended pregnancy.
• The POP, LNG-IUS, and implant are not associated with a significant increase in VTE risk and are first-line for women with a personal history of VTE or on anticoagulation; CHC is UKMEC 4 (contraindicated) in this group.
• This guideline itself is archived — if referenced in an exam context, cite current FSRH CHC guidance and the UKMEC risk-categorisation tables rather than GTG 40 directly.

Source: RCOG Green-top Guideline No. 40 (Archived — RCOG now directs (RCOG GTG 40 published July 2010, subsequently archived.)

Read the original on rcog.org.uk

Clinically reviewed by NHS obstetricians and gynaecologists · Source last updated RCOG GTG 40 published July 2010, subsequently archived.

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