Birth Control
Skipping Periods on the Pill: Is Continuous Birth Control Safe?
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The link between oestrogen-containing contraceptives and venous thromboembolism (VTE) — the medical term for blood clots in veins — is one of the most documented risks in hormonal contraception. It is also one of the most frequently misunderstood. The absolute risk for most healthy women is low, but the assessment process matters. Here is how Zoey's medical team approaches it.
Venous thromboembolism encompasses two related events: deep vein thrombosis (DVT), where a clot forms in a deep vein (usually in the leg), and pulmonary embolism (PE), where that clot travels to the lungs. Both are serious medical events, though PE is the more immediately life-threatening.
Oestrogen increases the production of clotting factors in the blood — a biological feature that historically served to limit blood loss during childbirth. In the context of combined hormonal contraceptives, this effect raises the background risk of VTE. The absolute numbers provide useful context: without contraception, the background VTE rate in reproductive-age women is approximately 2 per 10,000 women per year. On combined oral contraceptives, this rises to roughly 3-9 per 10,000 per year depending on the progestin type. For comparison, the risk during pregnancy is approximately 5-20 per 10,000, and in the postpartum period it is higher still.
These are not trivial risks to dismiss, but they are also substantially lower than risks many people accept without calculation. The clinical task is to identify which women carry elevated baseline risk — where the combined effect of oestrogen plus individual risk factors pushes total risk to an unacceptable level.
When a Singapore-licensed doctor evaluates you for a combined hormonal contraceptive, the following factors are systematically reviewed:
Personal or family history of VTE. A previous DVT or PE substantially increases your risk of recurrence. A first-degree family member (parent, sibling) with VTE — particularly if it occurred at a young age or without an obvious trigger (such as surgery or long-haul travel) — may indicate an underlying clotting disorder. This prompts further assessment, potentially including thrombophilia screening.
Inherited thrombophilias. Conditions such as Factor V Leiden mutation, Prothrombin G20210A mutation, Protein C or S deficiency, or antithrombin deficiency significantly amplify VTE risk in combination with oestrogen. Combined pills are generally contraindicated for women with these conditions.
Obesity (BMI ≥ 30 kg/m²). Elevated BMI independently raises VTE risk through several mechanisms including reduced venous blood flow and inflammation. Combined with oestrogen, the risk increases further.
Prolonged immobility. Long-haul flights, hospitalisation, or extended bed rest reduce blood flow in the legs and raise VTE risk. This is situational rather than a background risk factor, but women on combined contraceptives should be aware and take standard precautions (hydration, movement, compression stockings) during long travel.
Age over 35. Background cardiovascular risk increases with age. Combined with oestrogen, the risk-benefit assessment shifts, particularly when other risk factors are also present.
Smoking. While smoking primarily increases arterial rather than venous clot risk, it interacts with overall cardiovascular risk and is a standard part of the assessment.
Progestin type. As noted in the research literature, some progestins — including desogestrel, gestodene, and drospirenone — are associated with modestly higher VTE rates compared to levonorgestrel-containing pills. For women at higher baseline risk, a levonorgestrel-containing pill may be preferred if a combined method is appropriate at all.
For women where combined hormonal contraceptives are not appropriate, progestin-only methods eliminate the oestrogen-driven component of VTE risk. These include:
The copper IUD (non-hormonal) carries no VTE risk and offers highly effective contraception without any hormonal component.
If you have a personal or family history of blood clots, a known clotting disorder, BMI above 30, or other risk factors listed above — and you are currently using or considering a combined hormonal contraceptive — discuss your individual risk profile with a Singapore-licensed doctor. This is not a reason to panic about your current contraception, but it is a reason to ensure the assessment has been done properly.
How common are blood clots on the pill — really? The absolute risk is low. On combined oral contraceptives, the estimated rate of VTE is approximately 3-9 per 10,000 women per year, compared to a background rate of around 2 per 10,000 in non-users. The risk is higher than background but substantially lower than during pregnancy. Most women who take the pill never experience a clot; the concern is significant only when combined with other risk factors.
Does the pill type affect blood clot risk? Yes. Pills containing levonorgestrel carry a lower VTE risk compared to those with drospirenone, desogestrel, or gestodene, based on available evidence. This is one reason doctors may choose a specific progestin type for women at moderate baseline risk. The difference in absolute terms remains small for most healthy women.
What symptoms of a blood clot should I look out for while on the pill? Seek urgent medical attention if you experience: sudden swelling, pain, or redness in one leg; unexplained shortness of breath; chest pain; or rapid heartbeat. These may be signs of DVT or pulmonary embolism. Do not wait for a routine appointment — go to an emergency department.
Zoey is a doctor-led telehealth platform for women's health in Singapore. Consultations with Singapore-licensed doctors available online. Treatments are prescription-only medicines (POMs) and require medical assessment.
Articles featured on Zoey are for informational purposes only and should not be constituted as medical advice, diagnosis or treatment. If you have any medical questions or concerns, please talk to your healthcare provider. If you're looking for a healthcare provider, click here.
