DRCOG Question Bank

The primary mechanism of action of the COC is suppression of ovulation through inhibition of the hypothalamic-pituitary-ovarian (HPO) axis, as stated in FSRH guidelines on combined hormonal contraception. The oestrogen component suppresses follicle-stimulating hormone (FSH), preventing follicular development, while the progestogen component suppresses the luteinising hormone (LH) surge, preventing ovulation. Secondary mechanisms include thickening of cervical mucus making it hostile to sperm penetration, thinning of the endometrium reducing receptivity to implantation, and reduced tubal motility. All these mechanisms work together to provide highly effective contraception with a failure rate of less than 1% with perfect use. The COC contains synthetic oestrogen (usually ethinylestradiol 20-35 micrograms) and a progestogen. Different progestogens include levonorgestrel, norethisterone, desogestrel, gestodene, and drospirenone, each with slightly different side effect profiles. The COC is UKMEC category 1 for healthy women without risk factors.

Remember: The COC primarily works by suppressing ovulation via HPO axis inhibition - secondary mechanisms include cervical mucus thickening and endometrial thinning, but ovulation suppression is the key mechanism.

According to FSRH guidelines on quick starting contraception, the COC can be started at any point in the menstrual cycle if it is reasonably certain the woman is not pregnant, but additional contraceptive precautions (barrier methods) are required for the first 7 days. If started on days 1-5 of the menstrual cycle, no additional precautions are needed as ovulation has not yet occurred. Quick starting improves uptake and continuation rates by removing the barrier of waiting for the next period. A pregnancy test should be performed at the time of quick starting if there has been any risk of pregnancy, and a follow-up pregnancy test is recommended 3 weeks after the last episode of UPSI. If UPSI has occurred before quick starting and it is outside the first 5 days, emergency contraception should be considered before starting. Ulipristal acetate EC requires a 5-day gap before starting hormonal contraception, whereas levonorgestrel EC allows immediate quick start.

Remember: Quick start the COC any day of the cycle with 7 days of additional contraception - but if starting days 1-5, no extra precautions are needed.

Per FSRH UKMEC (2016, amended 2019), multiple risk factors for arterial cardiovascular disease - including older age, smoking, obesity, hypertension, diabetes, and dyslipidaemia - make combined hormonal contraception (CHC) UKMEC 3 (risks generally outweigh advantages). This 38-year-old has three relevant ASCVD risk factors stacked together: age ≥35, smoking 10 cigarettes per day, and BMI 36.

Individual UKMEC categories for CHC: smoking <15/day at age ≥35 = UKMEC 3; smoking ≥15/day at age ≥35 = UKMEC 4; BMI 35–39 kg/m² = UKMEC 3; BMI ≥40 = UKMEC 4. Where multiple ASCVD risk factors coexist, FSRH guidance is that categories should not simply be summed but considered together - the combination is generally classed as UKMEC 3, with clinicians upgrading to UKMEC 4 only when the cumulative risk is judged unacceptable. UKMEC 4 (absolute contraindication) is reserved for situations such as current or past breast cancer, migraine with aura, current VTE, established cardiovascular disease, and smoking ≥15/day at ≥35.

Safer alternatives that are UKMEC 1 or 2 for this patient include the progestogen-only pill, the etonogestrel implant (Nexplanon), the LNG-IUS (e.g., Mirena), the copper IUD, and DMPA injection (UKMEC 2 if BMI ≥35). Address modifiable risk via NHS smoking cessation support (NICE NG209) and weight management (NICE CG189).

Remember: Multiple ASCVD risk factors stacking → CHC is UKMEC 3, not automatically UKMEC 4; smoking ≥15/day at age ≥35 is the threshold that pushes CHC to UKMEC 4; LARC (implant, IUS, IUD) are UKMEC 1 here and should be offered as safer alternatives.