Contraception

Published on 09/03/2015 by admin

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Last modified 09/03/2015

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Chapter 7 Contraception

Caroline De Costa, Michael Flynn

A standard measure of contraceptive effectiveness is the Pearl index—the number of pregnancies per 100 woman-years in those at risk of pregnancy. One woman-year equals 12 menstrual cycles.

Natural methods

Natural methods are based on avoiding sexual activity that might lead to conception at the time when the ovum can be fertilised. It is necessary to predict the time of ovulation (generally by observing changes in body temperature) and to allow for the time that the sperm can survive with fertilising potential in the female genital tract. Intercourse is prohibited until 72 hours after the rise in basal body temperature. The Pearl index is 25/100 woman-years; with coitus interruptus, it is 18/100.

Barrier methods

Diaphragm

The diaphragm lies diagonally across the cervix, vaginal vault and anterior vaginal wall (extends from posterior vaginal fornix to behind pubic bone). Types of design are arcing, coil or flat; it is manufactured from natural rubber, latex or silicone.

Function

• acts as retainer of spermicide
• keeps sperm away from alkaline cervical mucus, as sperm die in the acidic pH of the vagina
• prevents physical aspiration of sperm into the cervix and uterus

Effectiveness

• with perfect use, Pearl index 6/100 (normally increased by 3–7 times)
• may be protective against some sexually transmitted diseases, but not human immunodeficiency virus (HIV)
• not suitable for women with anatomical abnormalities of the genital tract and those with large cystoceles, rectoceles or uterine prolapse

Cervical/vault caps

• three types: cervical, vault, vimule (both cervix and vault); manufactured from latex, silicone
• function: to occlude the cervix
• spermicides recommended with use
• Pearl index 7/100

Advantages

• can be used in the presence of genital prolapse
• no rim; therefore, not felt by partner
• fitting not changed by changes in the size of the vagina

Sponge

• function: release spermicide; absorb the ejaculate; block the cervix
• Pearl index 17/100

Condoms

• reduce transmission of sexually transmitted diseases, including HIV
• non-latex condoms (polyurethane) available
• Pearl index, with perfect use, 2/100

Female condoms

• cover the vulva and may protect against infections such as herpes simplex and human papillomavirus

Spermicides

• most commonly used is nonoxynol-9; newer agents: octoxynol, benzalkonium chloride
• act by disrupting sperm cell membrane, causing rupture of spermatozoa
• available in gels, foams, creams, pessaries and capsules
• variable efficacy depending on doses, formulations and compliance
• may protect against sexually transmitted disease, and have in vitro anti-HIV properties

Intrauterine contraceptive devices

Types

• copper, to increase effectiveness and reduce the surface area (e.g. Multiload 375, Slimline TT380)
• progestogen-containing device (e.g. levonorgestrel-releasing intrauterine device (LNG IUD))

Mechanisms of action

• both types: prevent fertilisation of the ovum
• both types: foreign body response in myometrium interferes with implantation of the blastocyst
• both types: interfere with sperm transport
• LNG IUD only: causes endometrial atrophy, thickening of cervical mucus, prevents or delays ovulation in some women; oligomenorrhoea or amenorrhoea a normal side effect

Effectiveness

• Copper devices have a Pearl index in the first year of 2–3/100, later falling to lower than 1/100.
• They can be used as a postcoital contraceptive.
• Progesterone devices have a failure rate of 0.2%.

Counselling

• Take a past medical, surgical and social history.
• Discuss risks.
• The ideal patient for the intrauterine contraceptive device is a multiparous, monogamous woman with regular, normal periods.

Before insertion

• Explain procedure and risks, and acquire consent.
• Conduct a general physical examination.
• Perform a vaginal/pelvic examination.
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