Population and birth control

The world's population grew from about 2 billion in 1900 to about 7.2 billion by 2011. India's crossed 1.2 billion in 2011. The main reason is good news: fewer people die, especially mothers in childbirth (the maternal mortality rate, MMR) and babies (the infant mortality rate, IMR), thanks to better health care. But with more people, there is more pressure on food, water, housing and jobs. One response is to help couples choose when and how many children to have: contraception.

An ideal contraceptive is easy to use, easy to get, effective, and reversible, with few or no side-effects, and it should not interfere with sexual desire.

All methods work by stopping the sperm and ovum from meeting, or stopping an embryo from implanting. The main groups:

• Natural methods: periodic abstinence, avoiding intercourse from about day 10 to day 17 of the cycle, when an ovum is most likely to be present; withdrawal; and lactational amenorrhea, the absence of periods while a mother is fully breastfeeding, which works only for up to six months after birth. These have no side-effects but fail more often.
• Barrier methods: physical barriers that stop sperms reaching the ovum. Condoms for males and females, made of thin rubber or latex, also protect against STIs and AIDS. Diaphragms, cervical caps and vaults are placed over the cervix.
• Intra-uterine devices (IUDs), placed in the uterus by a doctor. Non-medicated IUDs (Lippes loop); copper-releasing IUDs (CuT, Cu7, Multiload 375), where copper ions slow the sperms and reduce their ability to fertilise; and hormone-releasing IUDs (Progestasert, LNG-20), which also make the uterus unsuitable for implantation. IUDs are a good choice for spacing children.
• Oral pills: small doses of progestogens, or progestogen-estrogen mixtures, taken daily for 21 days. They stop ovulation and implantation. Saheli is taken once a week. Hormones can also be given as injections or implants under the skin.
• Emergency contraception: pills or an IUD within 72 hours of unprotected intercourse.
• Surgical methods (sterilisation): in men, vasectomy: a small part of the vas deferens is removed or tied; in women, tubectomy: the same is done to the fallopian tube. They block the passage of gametes and are very effective, but they are hard to reverse.

Every method is best chosen with a qualified doctor's advice, since some have side-effects such as nausea, abdominal pain or irregular bleeding.