Course 21.3Lesson 1 of 3

What each method of birth control protects against

No method of birth control is best at everything. Each blocks one step, suits one user, can or cannot be undone, and does or does not protect against infection. This lesson sets the methods side by side and shows how failure rates are read.

about 25 min1 simulation1 practice question

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Try the code and the simulations beside the lesson.

One chart, many methods

A clinic puts up a chart of the methods of birth control. Which one is the best? The honest answer is that it depends on what a person needs. A method is judged by four questions.

Which step does it stop? Ovulation, the meeting of the sperm and the ovum, fertilisation, the passage of the gametes, or implantation.
Who uses it? The male, the female, or the couple.
Can it be reversed? Almost all can. The surgical methods cannot be reversed easily.
Does it protect against infection? Among the methods of this chapter, the condom does.

The step that each method stops

Method	The step it stops
Lactational amenorrhea	ovulation, which does not take place in intense lactation
Periodic abstinence, withdrawal	the meeting of sperms and ovum
Condoms, diaphragm, cervical cap, vault	the meeting of sperms and ovum, by a barrier
Copper releasing IUD	the movement and the fertilising power of sperms
Hormone releasing IUD	the same, and also implantation and the cervix
Pills, injectables, implants	ovulation, implantation and the entry of sperms
Vasectomy, tubectomy	the passage of the gametes
Emergency methods	a pregnancy, when used within 72 hours of coitus

A table of ten methods of birth control with four columns: the method, who uses it, whether it is reversible, and whether it protects against sexually transmitted infections. Periodic abstinence: couple, reversible, no protection. Withdrawal: male partner, reversible, no. Lactational amenorrhea: mother, reversible, no. Condom: male or female, reversible, and yes, it protects, in a green row. Diaphragm, cap and vault: female, reversible, no. IUD: female, reversible, no. Pills: female, reversible, no. Injectables and implants: female, reversible, no. Vasectomy: male, reversal poor, no. Tubectomy: female, reversal poor, no.

Look at the last column of the picture. Only the condom protects against sexually transmitted infections. The pill, the IUD, the injection and the surgical methods stop a pregnancy, and they do nothing against an infection. This is one of the most common traps in questions.

Reversible and terminal methods

A reversible method can be stopped, and the person can then have a child. A terminal method is meant to be for good. Vasectomy and tubectomy are terminal. NCERT says that their reversibility is very poor.

Some methods are used only by one sex.

Male: the male condom, withdrawal and vasectomy.
Female: the diaphragm, the cap, the vault, the IUD, the pills, the injections and implants, and tubectomy.
Couple: periodic abstinence.

How well does a method work?

This part is not in the NEET syllabus, but A-Level, IB and public health courses use it. A failure rate says how many of 100 users become pregnant in the first year. The figures depend on how the method is used. Typical use includes mistakes and missed days. Perfect use has none. The table here uses typical use.

A horizontal bar chart of pregnancies in the first year among 100 women, for typical use. No method 85, withdrawal 20, male condom 13, combined pill 7, injectable 4, copper IUD 0.8, tubectomy 0.5, vasectomy 0.15 and implant 0.1. The bars of 10 or more are red, those from 3 to 10 are orange and the smaller ones are green. The value is written at the end of each bar.

The figures are those of a WHO handbook, and other sources give slightly different values. The pattern is the same in all of them. Some methods depend on the user to act each time, such as withdrawal or the condom. They fail more often than methods that work without a daily act, such as the IUD and sterilisation.

A failure rate of 13 in 100 does not mean that a method fails once in 8 years. The chance builds up over the years. If the chance in one year is $f$ , the chance of at least one pregnancy in $t$ years is $1 - (1 - f)^t$ .

You should find that a method with 13 pregnancies in 100 in the first year has a chance of about one half after 5 years, and about three quarters after 10 years.

Try it in Python

The program stores the failure rates in a dictionary. It finds the pregnancies expected in a group and the chance over a number of years.

Practise with new numbers

Common mistakes

Saying that the pill or the IUD protects against HIV. It does not. Only the condom does, among these methods.
Saying that a failure rate of 13 in 100 is the chance over the whole of the use. It is the chance in one year. The chance over several years is larger.
Saying that vasectomy removes the testes. It cuts the vas deferens. The testes remain.
Mixing up the users. The condom for the male, the diaphragm for the female, abstinence for the couple.
Thinking that a reversible method is also a protection against infection. These two facts are separate.

Remember these

A method is judged by the step it stops, its user, its reversibility and its protection against infection.
Only the condom protects against STIs, among the methods of this chapter.
Vasectomy and tubectomy are terminal. Reversal is very poor.
Failure rates are for the first year. The chance over $t$ years is $1 - (1 - f)^t$ .

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

Which method of this chapter also protects against sexually transmitted infections?

Name three methods that are used by the female only.

Which step does a vasectomy stop?

Why is periodic abstinence less reliable than an IUD?

What is the chance of at least one pregnancy in 2 years, if the chance in one year is 10 in 100?

References

World Health Organization and Johns Hopkins Bloomberg School of Public Health (2018). Family Planning: A Global Handbook for Providers, 3rd edition, the table of the effectiveness of family planning methods.
NCERT (2023). Biology, Textbook for Class XII, chapter 3, Reproductive Health.