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Recommendations for Contraceptive Use |
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Progestin-Only Injectables |
Q.1. When can the first progestin-only
injection be given (interval)? How soon does it become effective? Is a back-up method
needed?
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| a) Progestin-only injections may
be given any time you can be reasonably sure the woman is not
pregnant, for example, during the 7 days which begin with the onset of menses (days 1
through 7 of the menstrual cycle). |
a) Although ovulation can occur
as early as day 10 of the menstrual cycle, this is rare4. Fertile ovulation is
very uncommon before day 121. Intercourse 5 days before ovulation may have as
much as a 5% chance of resulting in pregnancy2; however, since experts believe
there are few fertile ovulations before day 13, there is only a very small chance that
intercourse on day 7 of the cycle could result in pregnancy1. In general, use of DMPA within the first 7 days after the woman's
normal menses would assure that the probability of the woman already being pregnant, or
becoming pregnant, is extremely low3.
The Technical Guidance Working
Group has reached this conclusion after a thorough review of the available literature and
consultation with the following experts:
William Collins, PhD, DSc, Department of Obstetrics and Gynecology, Kings College, UK
Jeffrey Spieler, MSc, Research Division, Office of
Population,USAID.
- Dixon GW, Schlesselman JJ, Ory HW,
Blye RP. Ethinyl estradiol and conjugated estrogens as postcoital contraceptives. Journal
of the American Medical Association 1980;244:1336-1339.
- Gray RH, Pardthaisong T, McDaniel EB,
Doyle P. The timing of the first injection of Depo Provera. IPPF Medical Bulletin
1975; 9(3): 3-4.
- Schiphorst LE, Collins WP, Roystar JP.
An estrogen test to determine the times of potential fertility in women. Fertility and
Sterility 1985;44:328-334.
Although injectable progestins have no known teratogenic
effects, avoiding the risk of fetal exposure is preferable on general principles. In
addition, one study has suggested that in utero exposure may increase the
risk of low birth weight babies.
- Simpson JL, Phillips OP. Spermicides,
hormonal contraception and congenital malformations. Advances in Contraception
1990;6:141-147.
- Bracken MB. Oral contraceptives and
congenital malformations in offspring: A review and meta-analysis of the prospective
studies. Obstetrics and Gynecology 1990;76:552-557.
- Pardthaisong T, Gray RH. In utero
exposure to steroid contraceptives and outcome of pregnancy. American Journal of
Epidemiology 1991;134(8):795-803.
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| b) For a woman having menstrual
cycles, no back-up method is needed if she is in the first 7 days of her menstrual cycle
and is still menstruating. If she is in the first 7 days of her cycle, but is not
menstruating, some programs may recommend use of a back-up method for 1 week. Injectables
may be started anytime you can be reasonably sure the woman is not
pregnant. However, if injections are started after day 7 of a regular cycle, a back-up
method (or abstinence) may be needed (see c., below). |
b) It is probable that
progestin-only injections effectively thicken cervical mucus within 24 hours. Consistent
with this theory, progestin-only pills have been shown to produce a thickened mucus with
low sperm penetration within 3 to 4 hours after pill ingestion. Natural progesterones also
cause cervical mucus to become scant, thick and sticky, decreasing or inhibiting sperm
penetration, usually within 24 hours, but sometimes within 48 hours. Clinical judgement is
also consistent with this theory.
- The Technical Guidance Working Group has reached this conclusion after a thorough review
of the available literature and consultation with the following experts:
Gary Grubb, MD, MPH, The RW Johnson Pharmaceutical
Research Institute, Raritan, NJ, USA
Michael Orme, Professor of Clinical Pharmacology,
TheUniversity of Liverpool, UK.
Wright SW, Fotherby K, Fairweather F.
Effect of daily small doses of Norgestrel on ovarian function. Journal of Obstetrics
and Gynaecology of the British Commonwealth 1970;77:65-68.
Tsibris JCM. Cervical mucus, in Gould
JJ, Josimovich JB (eds). Gynecologic Endocrinology. New York, Plenum Medical Book
Company, 1987, pp 175-183.
Insler V, Melmed H, Eichenbrenner I,
Serr D, Lunenfeld B. The cervical score: A simple semiquantitative method for monitoring
of the menstrual cycle. International Journal of Gynaecology and Obstetrics 1972;10(6):223-228.
Flynn AM, Lynch SS. Cervical mucus and
identification of the fertile phase of the menstrual cycle. British Journal of
Obstetrics and Gynaecology 1976(83):656-659.
Moghissi KS, Syner FN, Evans TN. A
composite picture of the menstrual cycle. American Journal or Obstetrics and Gynecology
1972;114(3):405-418.
DMPA and NET-EN consistently inhibit ovulation.
- Injectable Contraceptives: Their
Role in Family Planning Care. Geneva, World Health Organization, 1990.
- Mishell DR. Long-acting contraceptive
steroids: Postcoital contraceptives and antiprogestins, in Mishell DR, Davajan V, Lobo RA,
(eds). Infertility, Contraception, and Reproductive Endocrinology, 3rd edition.
Boston, Blackwell Scientific Publications, 1991, pp 872-894.
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| c) Although
there is good reason to believe the effect on cervical mucus will promptly provide
contraceptive protection within 24 hours, it may be prudent to consider a back-up method
for up to 7 days. (See Q.2. for postpartum initiation and Q.3. for post-abortion
initiation.) |
c) Some programs might recommend
a back-up method for women who are not menstruating at the time of progestin-only
injectable initiation because there is a very slight risk of conception from unprotected
intercourse on day 7 of the cycle. |
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