Last Updated: 19 March 2015

 

What is Birth Control?

How Does Birth Control Prevent Pregnancy?

Can Birth Control Cause Abortions?

How Do Hormonal Contraceptives Work? 

How Do Interuterine Devices (IUDs) Work?

 

What is Birth Control?

Birth control refers to contraception.  Contraception is any substance, device or method used to artificially or naturally prevent pregnancy. Examples of artificial birth control are hormonal contraceptives (the pill, injections, rings, patches and implants, emergency contraception), contraceptive barrier methods (condoms, diaphragms, spermicides, cervical caps) and other devices or methods such as interuterine devices (IUDs), vasectomy or tubal ligation. Examples of natural birth control include abstience and natural family planning.  

 

How Does Birth Control Prevent Pregnancy?

The purpose of contraception is to prevent sperm and ovum from joining, i.e. prevent fertilisation, which is the beginning of a pregnancy.  However some forms of contraception will not only act to prevent fertilisation but may also have the effect of terminating a new pregnancy (an abortion).  

 

Can Birth Control Cause Abortions?

The question of whether a particular contraception may cause an abortion, i.e. be an 'abortifacient', depends on whether it may act to prevent implantation of a new embryo, if it is used after fertilisation has already occurred (i.e. the woman is already pregnant) or if a woman becomes pregnant while using the contraception (it fails to prevent fertilisation).  If a new embryo is prevented from implanting into the wall of the uterus, the embryo is essentially starved of nourishment and dies.

Contraceptive barrier methods, including condoms, diaphragms, cervical caps, spermicide, vasectomy and tubal ligation form either a chemical or physical barrier to prevent sperm reaching an ovum which is the limit to how they work. They will either succeed in preventing fertilisation or fail to do so.  If pregnancy does occur, these contraceptive barrier methods will not interfer with implantation of a new embryo and hence are not abortificants.

Likewise, natural family planning such as the Billings Ovulation Method or the Creighton Method (Napro Technology) and abstience are methods which, without surgical or artificial means, make it impossible or significantly reduce the possibility of a sperm successfully reaching an ovum.  These methods have no further action but to prevent fertilisation and are never abortificants.

Regarding other contraceptives, namely hormonal contraceptives and intrauterine devices, it is necessary to look closely at the latest research and advice from experts to determine if they may act as abortificants or not.

 

How Do Hormonal Contraceptives Work?

The Pill

The pill is a hormonal contraception which must be taken regularly to be effective.  Common oral contraceptive pills (OCP) are:

  1. Progestin-only Pill (POP) - uses a progestin (mimics the progesterone hormone), e.g. levonorgestrel or norethisterone.  It is also called the Mini-pill. E.g. Micronor, Femulen & Microval.
  2. Combined Oral Contraceptive Pill (COCP) - uses a synthetic estrogen (usually ethinyl estradiol) and a progestin (either levonorgestrel or norethisterone or a third generation progestin - gestodene or desogestrel).  There are 3 main subtypes: 
    1. Monophasic - same amount of hormones in all 21 pills of the 21 day pill cycle. E.g. OrthoCyclen, Alesse, Loestrin
    2. Biphasic - two different alternating levels of hormones in the pill cycle. E.g. Mircette, Ortho Novum 10/11
    3. Triphasic - three different alternating hormone levels in the pill cycle.  E.g. Tri-Levelen, ortho TriCyclen & Triphasal
  3. Extended-cycle Birth Control Pill - also known as Extended-cycle Pill. This newest type of pill is also a combined contraceptive pill (containing estrogen and progestin).  Designed for continuous use, it reduces the number of periods a woman has or elimates them completely. E.g. Lybrel, Seasonale, Seasonique.

How effective the pill is varies because all women are different.  However, all types of the pill, when taken consistently, may work in the following ways:

  1. Prevent ovulation.  Ovulation releases an egg.  If this is prevented, there is no egg so fertilisation can't occur.  While the synthetic hormones in the pill act to decrease natural hormones which act to cause ovulation, they don't completely stop the natural hormones.  Hence some women who take the pill still ovulate and become pregnant.  Particularly if a woman doesn't take the pill at the same time each day or misses pills, the balance of hormones is not maintained and pregnancy may occur.
  2. Thicken the cervical mucus.  This acts to prevent fertilisation because sperm can't easily pass through the mucus to reach an egg in the fallopian tube.
  3. Alter the endometrium (uterine lining).  The pill also causes a thinning and change in quality of the uterine lining which theoretically could make implantation of a new embryo difficult if fertilization does occur.  However, for fertilization to occur, ovulation must occur first and the immediate effect of the natural hormones released through ovulation is to thicken the uterine lining in preparation for a possible pregnancy.  There is no scientific evidence1 that the pill acts to prevent implantation and may be an abortificiant .

 

 

Implants, Injections, Rings and Patches

Implants, injections, rings and patches are all hormonal contraceptives and hence work in the same ways as described for the oral contraceptive pill.  The main way they work are to prevent ovulation and also inhibit sperm function.  There is no scientific evidence that these prevent implantation and hence cause abortions.

Implants: E.g. Implanon, a rod 4cm x 2mm which contains 68mg of etonorgestrel (a synthetic progestogen) which is inserted under the skin of the upper inner arm.  The rod releases the synthetic hormone consistently into the woman's body and is effective for 3 years after which it must be surgically removed.  

Injections: E.g. Depo Provera, contains a dosage of the hormone medroxyprogesterone acetate (a synthetic form of the naturally occurring hormone progesterone) into muscle where it is slowly released (and is effective) for 3 months.  

Contraceptive rings: Vaginal rings which release a combination of synthetic hormones directly into the woman's body.  They work in the same way as the Combined Oral Contraceptive Pill, except that the woman does not have to take a pill daily.  The ring is left in place for three weeks and then removed for a single week after, replaced, etc.

Patches:  Contraceptive patches such as Evra stick to a woman's skin and release doses of hormones transdermally (through the skin).  Once again they work in a similar way to the Combined Oral Contraceptive Pill and may prevent ovulation, thicken the cervical mucus, cause thinning of the uterine lining and possibly impair tubal transport.

 

Emergency Contraception

Emergency contraception refers to any substance or device that is used to prevent pregnancy after unprotected intercourse.  The most common EC is the Emergency Contraception Pill (ECP), commonly known as the Morning After Pill or 'Plan B'.  ECPs are different to the abortion pill, which uses a different drug and works differently.

The main active ingredient used in ECPs is either levonorgestrel (LNG) or ulipristal acetate (UPA).  

Levonorgestrel ECPs include:

  • Morning After Pill, Postinor-2™
  • Plan B One-Step 
  • Next Choice One Dose
  • Next Choice
  • Levonorgestrel Tablets

There has been much debate about whether ECPs may be abortificants.  Some studies claim they cannot while others claim evidence shows they may affect the process &/or environment which allows an embyro to successfully implant.  The International Federation of Gynecology & Obstetrics (FIGO) and International Consortium for Emergency Contraception (ICEC) released a joint statement2 on the mechanism of action of levonorgestrel-only ECPs.  It concludes, 'inhibitation or delay of ovulation is LNG ECPs principal and possibly only mechanism of action.'  Also, ' Review of the evidence suggests that LNG ECPs cannot prevent implantation'.  

However research published in 2011 by Informa UK questions the conclusions made by this joint statement based on the same evidence from a significant number of studies referenced in the statement.  "How do levonorgestrel-only emergency contracepive pills prevent pregnancy? Some considerations"3 reviewed the studies referenced in the FIGO and ICEC statement and points out that the evidence from a significant number of these do not in fact support its conclusion that LNG ECPs avoid pregnancies only by inhibiting ovulation.  This research concludes that the evidence from studies referenced in FIGO/ICEC statement is inadequate to make conclusions on the affects of LNG ECPs on ovulation.
See "Can Levonorgestrel-Only Emergency Contraception Prevent Implantation?" for a further discussion on this research.  

With experts disagreeing on evidence of the mechanisms of action of LNG Emergency Contraceptive Pills, it is at this time unclear whether these ECPs may affect implantation and hence act as an abortificant (cause abortion). 

At present, FDA labelling says, "In addition, it [Plan B] may inhibit implantation (by altering the endometrium)."

 

Ulipristal acetate (UPA) Pills:

  • Ella, called Ella-1 in Europe

The main mechanisam of action of UPA pills is to delay or prevent ovulation.  However, unlike levonorgestrel, it has a direct, local effect to inhibit follicular rupture (i.e. ovulation) which allows it to be effective even when administered shortly before ovulation.

As with levonorgestrel, it is unclear whether UPA has an effect other than on ovulation, i.e. whether it may adversely affect the fallopian tube, the endometrium (uterine lining) or implantation or development of a new embryo.  A 2010 study4 of UPA found that at certain doses, it can decrease the thickness of the endometrium by 0.6 to 2.2mm but the study did not conclude whether this would prevent the implantation of a fertilised ovum.

Hence it is unclear at this time whether UPA ECPs may affect implantation and hence act as an abortificant.

 

Mifepristone RU-486, 'The Abortion Pill':

Mifepristone is also known as RU-486.  It only became available in Australia through chemists in 2013 and may be used as an EC , although it has not traditionally been used as such.  Evidence shows it not only can inhibit implantation and but will also detach implanted embryos so it is clearly an abortificant.

RU-486 is correctly referred to as the 'abortion pill' because if fertilisation has occurred and the pill is taken, it will detach implanted embryos, effectively destroying them.   Hence, RU-486 will cause an abortion if it is taken after fertilisation has already occurred.

 

Interuterine Devices (IUDs)

 

Hormonal IUD (Mirena)

 The hormonal IUD works in the same way as described for the oral contraceptive pill.  As a foreign interuterine device it also acts to prevent implantation of a new embryo if ovulation and fertilisation do occur.  Foreign devices in the uterus have been observed6 to cause to the endometrium (lining of the uterus) mucus accumulation on the surface, erosions or ulcers or even death of the endometrium and bleeding.  Hence Hormonal IUDs act to prevent implantation and hence may cause abortions.

 

 

Copper Intrauterine Device (Cu-IUD) (ParaGard)

Copper IUD's mainly prevent fertilization by interfering with sperm function but evidence unanimously shows that this contraception may also prevent implantation of an embryo if fertilisation has already taken place.  As a very recent study5 describes:  "The main mechanism of action of an CU-IUD is to prevent fertilisation through the effect of CU ions on sperm function.  In addition, if fertilisation has already occurred, CU ions influence the female reproductive trade and prevent endometrial receptivity".  

This study confirms earlier scientific research6 on how different types of IUD's work where the author's concluded that 'the antifertility effect of an interuterine foreign body must prevent the embryo from implantation".  Hence Cu-IUD's or any other type of Intrauterine Device (IUD) may be an abortificant.  

 

 

1  Rivera R, Yacobson I, Grimes D. The mechanism of action of hormonal contraceptives and intrauterine contraceptive devices. 1999 Nov; 181(5 Pt 1): 1263-9. http://www.ncbi.nlm.nih.gov/pubmed/10561657

2 International Federation of Gynecology & Obstetrics (FIGO), International Consortium for Emergency Contraception (ICEC). Statement on mechanism (October 2008). http://www.cecinfo.org/custom-content/uploads/2014/01/ICEC_MoA_Statement_3-28-12.pdf 

3  Mozzanega, B, Cosmi, E. How do levonorgestrel-only emergency contraceptive pills prevent pregnancy? Some considerations. Gynecological Endocrinology 2011;27(6):439-442.  http://informahealthcare.com/doi/abs/10.3109/09513590.2010.501885

4  Stratton P, Levens E, Hartog B, Piquion J, Wei Q, Merino M, Nieman L. Endometrial effects of a single early luteal dose of the selective progesterone receptor modulator CDB-2915. Fertility and Sterility 2010;93:2035-2041. http://www.ncbi.nlm.nih.gov/pubmed/19200989

5  Gemzell-Danielsson K, Berger C, P G L L. Emergency contraception - mechanisms of action.Contraception 2013;87:300-308.  http://www.ncbi.nlm.nih.gov/pubmed/23114735

6 Ding SL. Mode of action of intrauterine devices. 1983; 3(3):44-8. http://www.ncbi.nlm.nih.gov/pubmed/12267401

 

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