Methods of Birth Control and Sexually Transmitted Infections
Methods of birth control and sexually transmitted infections is IGCSE-specific detail requiring named contraceptive methods sorted by mechanism (hormonal, barrier, surgical and natural), an evaluation of their relative effectiveness, and named STIs with their mode of transmission and prevention. Beyond GCSE, students must explain the mechanism of each contraceptive method (not just name it), evaluate methods against each other for a given scenario, and explain, for a named STI such as HIV or chlamydia, how transmission occurs and how methods such as barrier contraception reduce the risk.
Before you start
Make sure you're comfortable with these topics first:
Method
- Sort contraceptive methods into four categories and give the mechanism for each named method: hormonal (the contraceptive pill and the implant/injection, which use oestrogen and/or progesterone to inhibit FSH and/or LH, preventing egg maturation or ovulation, as covered in the menstrual cycle topic); barrier (the condom and the diaphragm, which physically prevent sperm reaching an egg); surgical (male sterilisation/vasectomy, cutting the sperm ducts so sperm cannot reach the semen; female sterilisation, cutting or tying the oviducts so eggs cannot reach the uterus); natural (the rhythm method, avoiding intercourse during the fertile part of the cycle, identified from body temperature and cervical mucus changes; and abstinence).
- Learn that effectiveness is usually quoted as a percentage and that hormonal and surgical methods are generally more effective than barrier methods, which are more effective than natural methods, but that barrier methods (specifically the condom) are the only method on this list that also reduces the transmission of STIs.
- For evaluation questions, weigh named methods against explicit criteria given in the question (effectiveness, reversibility, cost, side effects, STI protection) rather than giving a generic list of pros and cons; a sterilisation is highly effective but not reversible, a condom is less effective at preventing pregnancy but is the only method that also reduces STI risk, and a hormonal method is effective and reversible but can have side effects and gives no STI protection.
- Learn named STIs and their mode of transmission: HIV (human immunodeficiency virus) is transmitted through the exchange of bodily fluids, including during unprotected sexual intercourse, sharing needles, or from mother to child during pregnancy/birth/breastfeeding, and can progress to AIDS if untreated; chlamydia (a bacterial infection) is transmitted through unprotected sexual contact and is often symptomless, which is why untreated infection can spread and, in women, can cause infertility by scarring the oviducts.
- Explain prevention in terms of blocking the transmission route: because HIV and chlamydia are spread through the exchange of bodily fluids during intercourse, using a condom acts as a physical barrier that reduces the risk of exchange, and regular STI screening allows early (often symptomless) infections to be treated before they spread further or cause complications.
- When a question asks to compare an STI's biological effect with its social/health impact, separate the two clearly: the biological effect is what the pathogen does in the body (for example, chlamydia scarring the oviducts), while the wider impact might include reduced fertility, the cost to health services of treatment, or the ongoing risk of further transmission if undiagnosed.
Worked example
A health advisor is asked to recommend a contraceptive method for a couple who want reliable protection against pregnancy AND protection against sexually transmitted infections, since they have recently started a new relationship. Explain which single method, or combination of methods, best meets both requirements, and justify your answer.
- Identify the two requirements separately: (1) reliable pregnancy prevention, (2) protection against STIs.
- Recall which method category gives STI protection: only barrier methods, specifically the condom, provide a physical barrier that reduces the exchange of bodily fluids and therefore STI transmission.
- Recall that condoms alone are less effective at preventing pregnancy than hormonal or surgical methods.
- Consider combining methods: using a condom together with a hormonal method (such as the contraceptive pill) would give the higher pregnancy-prevention effectiveness of the hormonal method while still gaining the STI protection from the condom.
- Final answer: recommend combined use of a condom and a hormonal method (for example, the contraceptive pill); the hormonal method inhibits FSH/LH to reliably prevent ovulation, while the condom is the only method that also acts as a barrier against the exchange of bodily fluids, reducing STI transmission risk, which a hormonal method alone would not provide.
Practice questions
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Q1Name one barrier method of contraception.Show answer
Answer: The condom (accept: the diaphragm).
Q2State the surgical method of contraception that involves cutting the sperm ducts.Show answer
Answer: Male sterilisation (vasectomy).
Q3State one contraceptive method that also reduces the risk of sexually transmitted infections.Show answer
Answer: The condom (barrier method).
Q4Name the pathogen type responsible for chlamydia, and state one method of transmission.Show answer
Answer: A bacterium; transmitted through unprotected sexual contact.
Q5Explain why chlamydia can cause infertility in women if left untreated.Show answer
Answer: Untreated chlamydia can spread and cause scarring/damage to the oviducts (fallopian tubes), which can block the tubes and prevent an egg meeting sperm, or prevent implantation.
Q6State one disadvantage of surgical sterilisation as a contraceptive method compared with a barrier method.Show answer
Answer: Sterilisation is not reversible (barrier methods can simply be stopped if the person wants to try to conceive).
Exam-style questions
Written in the style of a IGCSE Science exam paper, with a full mark scheme.
State two contraceptive methods that work by preventing sperm from reaching an egg without using hormones.
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A sexual health clinic screens 500 people for chlamydia. 60 test positive; of these, 42 report having no symptoms before the test. Calculate the percentage of chlamydia-positive people in this sample who were symptomless, and explain why this matters for the spread of the infection.
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Compare and evaluate a hormonal contraceptive method (such as the contraceptive pill) with a barrier method (such as the condom), considering effectiveness at preventing pregnancy, reversibility, and protection against sexually transmitted infections, and recommend which is more suitable for a couple in a new sexual relationship who are not yet ready to have children.
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Free printable worksheet
Want more practice on paper? Download the methods of birth control and sexually transmitted infections worksheet pack - 7 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 6 of IGCSE Science Workbook, the whole course as one free printable PDF.
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