Contraception and Abortion,Foes or Friends?

Wood J.J. , “Hormonal Contraception”, The New England Journal of Medicine, vol. 328, no. 21, May 27, 1993, pp. 1543–1547.

Hawkins D.F. , Elder M.G. , “Combined Oral Contraceptives, other Hormonal Contraceptive Procedures,” in Human Fertility Control. Theory and Practice, (London: Butterworth's, 1979), pp. 49-90, 91-125.

DiPietro M. L. , Sgreccia E. , “La Contragestanione Ovvero l'aborto Nascosto,” Medicna e Morale, vol. 38, no. 1, Gennaio-Febbraio 1987, pp. 5–34.

Chang M.C. , “Development of the Oral Contraceptives,” American Journal of Obstetrics and Gynecology, Vol. 132, No. 2, September 15, 1978, pp. 217–219.

Several investigators have studied more specifically the abortive effect of the estrogen-progestogen oral contraceptives: Ehmann R. , “Problems in Family Planning,” Anthropotes, Vol. 7, No. 1, Maggio 1991, pp. 95–126.

Hawkins D.F. , Elder M.G. , op. Cit, pp. 11–13. R. Guillemin. “Physiology and Chemistry of the Hypothalamic Releasing Factors for Gonadotropins: A New Approach to Fertility Control,” Contraception, vol. 122, no. 1, January 1972, pp. 1-19 J.W. Goldzieher, A. de la Peña, C.B. Chenault, A. Cervantes, “Comparative Studies of the Ethynyl Estrogens Used in Oral Contraceptives. Ill Effect on Plasma Gonadotropins,” American Journal of Obstetrics and Gynecology, vol. 122, no. 5 July 1, 1975, pp. 625-636.

The inhibition by combined oral contraceptives of the pituitary capcity to release LH and FSH in response to a stimulation by LH-RH (Luteinizing-Hormone-Releasing-Hormone) is clearly less important with the estradiol low dose pill than with the classic 50μg estradiol pill. Dericks-Tan J.S.E. , Krög W. , Aktories K. , Taubert H.D. , “Dose-Dependent Inhibition by Oral Contraceptives of the Pituitary to Release LH and FSH in Response to Stimulation with LH-RH+,” Contraception, Vol. 14, No. 2, August 1976, pp. 171–181.

Gaspard U.J. , Dubois M. , Gillain D. , Franchimont P. , Duvivier J. , “Ovarian Function is Effectively Inhibited by a Low-Dose Triphasic Oral Contraceptive Containing Ethinylestradiol and Levonorgestrel,” Contraception, Vol. 29, No. 4, April 1984, pp. 305–318. M. Elstein, P.G. Briston, M. Jenkins, D. Kirk, H. Miller, “Effects of Low-Estrogen Oral Contraceptive on Urinary Excretion of Luteinizing Hormone and Ovarian Steroids,” British Medical Journal, vol. I, no. 5896, 5 January 1974, pp. 11-13.

Spellacy W.N. , Kalra P.S. , Buhl W.C. , Birk S.A. , “Pituitary and Ovarian Responsiveness to a Graded Gonadotropin Releasing Factor Stimulation test in Women Using a Low-estrogen or a Regular Type of Oral Contraceptive,” American Journal of Obstetrics and Gynecology, Vol. 137, No. 1, May 1, 1980, pp. 109–115.

Refn H. , Kjaer A. , Lebech A.M. , Borggaard B. , Schierup L.K. , “Clinical and Hormonal Effects of Two Contraceptives: Correlation to Serum Concentrations of Levonorgestrel and Gestodene,” Contraception, Vol. 41, No. 3, March 1990, pp. 259–269.

Dericks-Tan J.S.E. , Schneider K. , Taubert H.D. , “The Mechanism ofr Action of a New Low-Dosed Combined Oral Contraceptive,” Archives of Gynecology, Vol. 229, No. 2, 1980, pp. 107–114.

Ling W.Y. , Johnston D.W. , Lea R.H. , Bent A.E. , Scott J.Z. , Toews M.R. , “Serum Gonadotropin and Ovarian Steroid Levels in Women During Administration of a Norethindrone-Ethinylestradiol Triphasic Oral Contraceptive, Contraceptive, Vol. 32, No. 4, October 1985, pp. 367–375.

Caillouette J.C. , Koehler A.L. , “Phasic Contraceptive Pills and Functional Ovarian Cysts,” American Journal of Obstetrics and Gynecology, Vol. 156, No. 6, June 1987, pp. 1538–1542, and the discussion by J. Spanos on pp. 1540-1541. J. Sapona, M. Elstein, W. Feichtinger, H. Sullivan, F. Lüdicke, U. Müller, B. Düsterberg, “Shorter Pill-Free Interval in Combined Oral Contraceptives Decreases Follicular Development,” Contraception, vol. 54, no. 2, August 1996, pp. 71-77.

Hansen et Lundvall have found such an interference in 21 women out of 70 using oral contraceptives and admitted nevertheless to having a legal abortion performed. Fotherby shows the wide variation in the “bioavailability” of ovarian sex hormones and synthetic analogues sued in oral contraception, depending on the rate and extent of absorption of the compound, its rate of metabolism, and its elimination. The bioavailability (total serum drug concentration in percentage of the administered amount) of ethinylestradiol varies, in different studies, from 43±16 to 74±25, with an overall mean value of 55% and a three-fold variability about the mean. A comparable variability is found with gestogens. Therefore, in some women who have short cycles, with a slower intestinal absorption rate of oral contraceptives, or with serum estrogen concentration higher than normal, the amount of administered estrogens may not be enough to prevent the growth of a follicle. If the combined gestogen reaches its serum peak too late, or if this peak is too low to prevent the LH surge at mid-cycle, ovulation can occur. Hansen T.H. , Lundvall F. , “Factors Influencing the Reliability of Oral Contraceptives,” Acta Obstetricia et Gynecologica Scandinavica, Vol. 76, No. 1, January 1997, pp. 61–64. K. Fotherby, “Bioavailability of Orally Administered Sex Steroids Used in Oral Contraception and Hormone Replacement Therapy. Contraception, vol. 54, no. 2, August 1996, pp. 59-69.

Elstein M. , Briston P.G. , Jenkins M. , Kirk D. , Miller H. , op cit.

8/22 in Killick (1987). 10/10 after 7 to 10 days pill-free period in Killick (1989), 11/30 in Hamilton and Hoogland (1989), 143/176 in Hoogland, et al. (1993) who found in 13% of cycles (23 over 176) a mean follicle diameter of 18.9 mm, 5 to 9/10 for each group often women in Grimes, et al. (1994), 21/31 in Van der Does et coll. (1995), 31 a 39 % of the patients during the first cycle in Egarter (1995), 9/22 in Crosignani, et al. (1996), 12/24 during the second cycle in Spona, et al. (1996), 20% in Rosmanith, et al. (1997). P.G. Crosignani, G. Testa, W. Vegetti, F. Parazzini, “Ovarian Activity Duirng Regular Oral Contraceptive Use. Contraception, vol. 54, no. 5, November 1996, pp/271-279. Ch. Egarter, M. Putz, H. Strohmer. P. Speiser, R. Wenzl, J. Huber, “Ovarian Function During Low-Dose Oral Contraceptive Use,” Contraception, vol. 51, no. 6, June 1995, pp. 329-333. D.A. Grimes, A.J. Godwin, A. Rubin. J.A. Smith, M. Lacarra, “Ovulation and Follicular Development Associated With Three Low-Dose Oral Contraceptives: A Randomized Controlled Trial,” Obstetrics and Gynecology, vol. 83, no. 1, January 1994, pp. 29-34. C.J. Hamilton, H.J. Hoogland, “Longitudinal Ultrasonographic Study of the Ovarian Suppression Activity of a Low-Dose Triphasic Oral Contraceptive During Correct and Incorrect Pill Intake,” American Journal of Obstetrics and Gynecology, vol. 161, no. 5, November 1989, pp. 1159-1162. H.J. Hoogland, S.O. Skouby, “Ultrasound Evaluation of Ovarian Activity Under Oral Contraceptives,” Contraception, vol. 47, no. 6, June 1993, pp. 583-590. S. Killick, E. Eyong, M. Elstein, “Ovarian Follicular Development in Oral Contraceptive Cycles,” Fertility and Sterility, vol. 48, no. 3, September 1987, pp. 409-413. S. Killick, “Ovarian Follicles During Oral Contraceptive Cycles: Their Potential for Ovulation,” Fertility and Sterility, vol. 52, no. 3/4, September/October 1989, pp. 580-582. B.G. Molloy, K.A. Coulson, J.M. Lee, J.K. Watters, “‘Missed Pill’ Conception: Fact or Fiction?”, British Medical Journal, vol. 290, no. 6480, 18 May 1985, pp. 1474-1475. W.G. Rossmanith, D. Steffens, G. Schramm, “A Comparative Randomized Trial on the Impact of Two Low-Dose Oral Contraceptives on Ovarian Activity, Cervical Permeability, and Endometrial Receptivity,” Contraception, vol. 56, no. 1, July 1997, pp. 23-30. J. Spona, W. Fechtinger, Ch. Kindermann, C. Wünsch, K. Brill, “Inhibition of Ovulation by an Oral Contraceptive Containing 100μg Levonorgestrel in Combination with 20μg Ethinylestradiol, Contraception, vol. 54, no. 5, November 1996, pp. 299-304. J. van der Does, N. Exalto, T. Dieben, H. Coelingh Bennink, “Ovarian Activity Suppression by Two Different Low-Dose Triphasic Oral Contraceptives, Contraception, vol. 52, no. 6, December 1995, pp. 357-361.

Once out of ten in Hamilton et Hoogland, 1989, four times out of thirty in Grimes et coll., 1994, once out of 32 in Van der does et coll., and in 4,1% of the observations of Rosmanith et coll., 1997.

1/10 pour Chowdhury V. (1980), 1/12 pour I.D. Nutall et coll. (1982), 1/11 pour Jung-Hoffmann et coll. V. Chowdury, U.M. Joshi, K. Gopalkrishna, S. Betrabet, S. Mehta, B.N. Saxena, “‘Escape’ Ovulation in Women Due to the Missing of Low Dose Combination Oral Contraceptive Pills,” Contraception, vol. 22, no. 3, September 1980, pp. 241-247. I.D. Nuttall, M. Elstein, “The Effect of Norethisterone (500 mcg) and Ethinyl Estradiol (35 mcg) Capsules on the Pituitary-Ovarian Axis,” Contraception, vol. 25, no. 5, May 1982, pp. 463-469. C. Jung-Hoffmann, F. Heidt, H. Kuhl, “Effect of Two Oral Contraceptives Containing 30μg Ethinylestradiol and 75 μg Gestodene or 150 μg Desogestrel Upon Various Hormonal Parameters,” Contraception, vol. 38, no. 6, December 1988, pp. 593-603.

Bowman J.A. Jr. , “The Effect of Norethindrone-Mestranol on Cervical Mucus,” American Journal of Obstetrics and Gynecology, Vol. 102, No. 7, December 1, 1968, pp. 1039–1040. M. Elstein, S.E. Morris, G.V. Groom, D.A. Jenner, J.J. Scarisbrick, E.H.D. Cameron, “Studies on Low-Dose Oral Contraceptives: Cervical Mucus and Plasma Hormone Changes in Relation to Circulating D-Norgestrel and 17α-Ethynyl Estradiol Concentrations, Fertility and Sterility, vol. 27, no. 8, August 1976, pp. 892-899. O. Widholm, U. Alapiessa, “The Biological Effects of a New Modified Sequential Oral Contraceptive,” Contraception, vol. 15. no. 1, January 1977, pp. 1-13.

Bregulla K. , Haußer H. , “Results of In Vitro Sperm Penetration Tests in Cervical Mucus in the Normal Cycle and in Mucus Under the Influence of the Contraceptive Pill,” Archiv für Gynäkologie, Band 218, Heft 3, 1975, pp. 227-32.

Hester L.L. Jr. , Kellett W.W. III , Spicer S.S. , Williamson H.O. , Pratt-Thomas H.R. “Effects of a Sequential Oral Contraceptive on Endometrial Enzyme and Carbohydrate Histochemistry,” American Journal of Obstetrics and Gynecology, Vol. 102, No. 6. November 15, 1968, pp. 771–783. O. Widholm, U. Alapiessa, “The Biological Effects of a New Modified Sequential Oral Contraceptive,” Contraception, vol. 15, no. 1. January 1977. pp. 1-13. B. Bayle, “L'activité Antinidatoire des Contraceptifs Oraux,” Contraception, Fertilité, Sexualité, vol. 22, no. 6, 1994, p. 392.

Friedrich E.R. , “Effects of Contraceptive Hormone Preparations on the Fine Structure of the Endometrium,” Obstetrics and Gynecology, Vol. 30, No. 2, August 1967, pp. 201–219.

Fedele L. , Marchini M. , Cavalli G. , Baglioni A. , Taccagni G.L. , “Marked Deciliation and Insufficient Secretory Modifications of Endometrial Surface During Treatment with a New Progestogen-Estrogen Combination,” Contraception, Vol. 35, No. 5, May 1987, pp. 497–505.

Rossmanith W.G. , Steffens D. , Schramm G. “A Comparative Randomized Trial on the Impact of Two Low-Dose Oral Contraceptives on Ovarian Activity, Cervical Permeability, and Endometrial Receptivity,” Contraception, 56, no. 1, July 1997, pp. 23–30.

Bayle B. , “L'activité Antinidatoire des Contraceptifs Oraux, op cit. P. 392. Pescetto, De Cecco, Pecorari. Ragni. Manuale di Ginecologia-Ostetricia, Vol. I, Roma, 1989, p. 316.

Di Pietro and Minacori give a 1.5 embryo destruction for a 15 year treatment with oral contraceptives. For B. Bayle, this loss would be of 3 to 10 embryos for 100 years/woman. Di Pietro M.L. , Minacori R. , op cit. P. 879. B. Bayle, op cit., p. 394.

Graham S. , Fraser I.S. , “The Progesterone-Only Mini-Pill, Contraception, vol. 26, no. 4, October 1982, pp. 373-388. P.W. Howe, “The Progestogen-Only Pill.” British Journal of Obstetrics and Gynecology, Vol. 92, No. 10. October 1985, pp. 1001–1002.

The progestogens at the present time are either estranes or gonanes which are all derivatives of 19-nortestosterone. The first to have been used orally in a continuous administration has been chlormadinone acetate (Martinez-Manatou et coll. 1966). The formulations in use today are Norethisterone (Noretrindrone, NET) (350 μg) or Levonorgestrel (LNG) (30 μg). Levonorgestrel is about ten times more potent as Norethisterone and combines more strongly to the receptors for progesterone. The doses of gestogens in the mini-pills are much lower than those in combined pills.

Sen A. (Late), Sanwal P.C. , Srivastava A.K. , Pande J.K. , Dasgupta P.R. , Kar A.B. , “Long Term Effect of a Continuous Daily Microdose of Norgestrel on the Genital Organs and Fertility of Female Rats.” Contraception, Vol. 2, No. 1, July 1970, pp. 59–67.

Martinez-Manautou J. , Giner-Velasquez J. , Cortes-Gallegos V. , Aznar R. , Rojas B. , Guttierez-Najar A. , Rudel H.W. , “Daily Progestogen for Contraception,” British Medical Journal, Vol. 2. no. 5554. 17 June 1967, pp. 730–732. K.S. Moghissi, C. Marks, “Effects of Microdose Norgestrel on Endogenous Gonadotropic and Steroid Hormones. Cervical Mucus Properties. Vaginal Cytology and Endometrium.” Fertility and Sterility, vol. 22. no. 7, July 1971, pp. 424-434. I.D. Nuttall, M. Elstein. D.R. Fahmy, “The Effect of Norethisterone Capsules on the Pituitary-Ovarian Axis,” Contraception, vol. 25, no. 1, January 1982, p. 51-57. J. Zañartu, A. Dabancens, C. Oberti. R. Rodriquez-Bravo, M. Garcia-Huidobro, “Low-Dosage Oral Progestogens to Control Fertility. I. Clinical Investigation,” Obstetrics and Gynecology, vol. 43, no. 1. January 1974, pp. 87-96.

Maruffo C.A. , Casavilla F. , Van Nynatten B. , Perez V. , “Modifications of the Human Endometrial Fine Structure Induced by Low-Dose Progestogen Therapy,” Fertility Sterility, Vol. 25, No. 9, September 1974. pp. 778–787.

Orr A.H. , Elstein M. , “Luteinizing Hormone Levels in Plasma and Urine in Women During Normal Menstrual Cycles and in Women Taking Combined Contraceptives or Chlormadinone Acetate.” The Journal of Endocrinology, Vol. 43, No. 4, April 1969, pp. 617–624. B.A. Mason, H.J.E. Cox, D.W. Mason. V. Grant, “Clinical and Experimental Studies with Low Doses of Megestrol Acetate,” Postgrad. Med. J., vol. 43, supplement, 1967, pp. 45-48. G.L. Foss, E.K. Svendsen, K. Fotherby, D.J. Richards, “Contraceptive Action of Continuous Low Doses of Norgestrel,” British Medical Journal, vol. 4, no. 5629, 23 November 1968, pp. 489-491. M.L'Hermitte-Balériaux, R. Hechtermans, D. Jacob, “Contraception Orale Continue par d-Norgestrel (30 gamma), Analyse des Variations des Taux des Gonadotropines et des Stéroïdes,” Journal de Gynécologie Obstétrique et Biologie de la Reproduction, vol. 2, no. 4, Juin 1973, pp. 347-355. B.M. Landgren, A. Balogh, M.W. Shin, M. Lindbergh, E. Diczfalusy, “Hormonal Effects of the 300μg Norethisterone (NET) Minipill. 2. Daily Gonadotropin Levels in 43 Subjects during a Treatment Cycle and During the Second Month of NET Administration,” Contraception, vol. 20, no. 6, December, 1979, pp. 585-605.

Landgren B.M. , Diczfalusy E. , “Hormonal Effects of the 300μg Norethisterone Minipill, Contraception, Vol. 21, No. 1, January 1980, pp. 87–113. S. Si, C. Jun-Kang, L. Chong-Hua. Y. Pei-Juan. Y. Qiu-Ying, F. Bao-Chuan, H. Mei-Li, G. You-Lun, L. La-Mei, K. Fotherby, “Effects of Different Doses of Norethisterone on Ovarian Function, Serum Sex Hormone Binding Globulin and High Density Lipoprotein-Cholesterol,” Contraception, vol. 47, no. 6, June 1993, pp. 527-537.

Aref I. , Hefnawi F. , Kandil O. , Abdel Aziz M.T. , “Effect of Minipills on Physiologic Responses of Human Cervical Mucus, Endometrium and Ovary,” Fertility and Sterility, Vol. 24, No. 8, August 1973, pp. 578–583. K.S. Moghissi, C. Marks, “Effects of Microdose Norgestrel on Endogenous Gonadotropic and Steroid Hormones, Cervical Mucus Properties, Vaginal Cytology, and Endometrium,” op, cit., p. 429. K.S. Moghissi, F.N. Syner. L.C. McBride, “Contraceptive Mechanism of Microdose Norethindrone,” Obstetrics and Gyenecology, vol. 41, no. 4, April 1973, pp. 585-594.

Nuttall I.D. , Elstein M. , Fahmy D.R. , op cit., p. 53.

Chretien F.C. , Sureau C. , Neau C. , “Experimental Study of Cervical Blockade Induced by Continuous Low-Dose Oral Progestogens,” Contraception, Vol. 22, no. 5, October 1980, pp. 445–456.

Kesserü E. , Larrañaga A. , “In Vitro Sperm Migration in the Human Cervical Mucus with Different Contraceptive methods, Contraception, Vol. 3, No. 3, March 1971, pp. 195–208.

Graham S. , Fraser I.S. , op cit., p. 374. E. Mears, M.P. Vessey, L. Andolšek, A. Oven, “Preliminary Evaluation of Four Oral Contraceptives Containing only Progestogens,” British Medical Journal, vol. 2, No. 5659, 21 June 1969, pp. 730-734.

Boettcher B. , “A Possible Mode of Action of Progestagen-Only Oral Contraceptives, Contraception, Vol. 9, No. 2, February 1974, pp. 123–131.

Bonnar J. , “Progestogen-Only Contraception and Tubal Pregnancies,” British Medical Journal, Vol. 1, No. 5902, 16 February 1975, p. 287. P. Bergsjø, H. Langengen, J. Aas, “Tubal Pregnancies in Women Using Progestagen-Only Contraception,” Acta Obstetricia et Gynecologica Scandinavica, vol. 53, no. 4, 1974, pp. 377-378. D.F. Hawkins, “Progestogen-Only Contraception and Tubal Pregnancies,” British Medical Journal, vol. 1, no. 5904, 2 Marxh 1974, p. 387. P. Liukko, R. Erkkola, L. Laakso, “Ectopic Pregnancies During Use of Low-Dose Progestogens for Oral Contraception,” Contraception, vol. 16, no. 6, December 1977, pp. 575-580. B.W.J. Mol, W.M. Ankum, P.M.M. Bossuyt, F. Van der Veen, “Contraception and the Risk of Ectopic Pregnancy: A Meta-Analysis,” Contraception, vol. 52, no. 6, December, 1995, pp. 337-341. R. Zarcone, G. Vicinanza, E. Carfora, N. Colacurci, “Gravidanza Extrauterina: Epidemiologia ed Eziolgia,” Minerva Ginecologia, vol. 48, no. 7/8, Luglio-Agosto 1996, pp. 283-286.

Beral V. , “An Epidemiological Study of Recent trends in Ectopic Pregnancy,” British Journal of Obstetrics and Gynaecology, Vol. 82, No. 10, October 1975, pp. 775–782.

Bergsjø P. , Langengen H. , Aas J. , op cit., p. 378.

Oberti C. , Dabancens A. , Garcia-Huidobro M. , Rodriguez-Bravo R. , Zanartu J. , “Low Dosage Oral Progestogens to Control Fertility. II. Morphological Modifications in the Gonad and Oviduct,” Obstetrics and Gynecology, Vol. 43, No. 2, February 1974, pp. 285–294.

Kim-Bjorkland T. , Landgren B.M. , Johannisson E. , “Morphometric studies of the Endometrium, the Fallopian Tube and the Corpus Luteum During Contraception with the 300 μg Norethisterone (NET) Minipill,” Contraception, Vol. 43, No. 5, May 1991, pp. 459–475.

McCann M.F. , Potter L.S. , “Progestin-Only Oral Contraception: A Comprehensive Review,” Contraception, Vol. 50. no. 6, supplement 1, December 1994, S9–S195.

Maruffo C.A. , Casavilla F. , Van Nynatten B. , Perez V. , op cit.

Sen A. (Late), Sanwal P.C. , Srivastava A.K. , Pande J.K. , Dasgupta P.R. , Kar A.B. , op cit., p. 64, table III.

Maqueo M. , Gorodovsky J. , Rice-Wray E. , Goldzieher J.W. , “Endometrial Changes in Women Using Hormonal Contraceptives for Periods Up to Ten Years,” Contraception, Vol. 1, No. 2. February 1970, pp. 115–129.

Starup J. , “Endometrial Histology and Vaginal Cytology During Oral Contraception,” Acta Obstetricia et Gynecologica Scandinavica, Vol. 46, No. 3, 1967, pp. 419–428.

Moghissi K.S. , Syner F.N. , McBride L.C. , op cit., p. 591. K.S. Moghissi, C. Marks, op cit., p. 431 E. Johannison, B.M. Landgren, E. Diczfalusy, “Endometrial Morphology and Peripheral Steroid Levels in Women With and Without Intermenstrual Bleeding During Contraception With the 300μg Norethisterone (NET) Minipill,” Contraception, vol. 25, no. 1, January 1982, pp. 13-30.

Maruffo C.A. , Casavilla F. , Van Nynatten B. , Perez V. , op cit. pp. 785–786.

Sen A. (Late), Sanwal P.C. , Srivastava A.K. , Pande J.K. , Dasgupta P.R. , Kar A.B. , op cit., pp. 61–65.

. Graham S. , Fraser I.S. , op cit., pp. 376–377. Pescetto, De Cecco, Pecorari, Ragni, Manuale do Ginecologia-Ostericia, vol. I, Roma, 1989, p. 316.

Howe P.W. , op cit., p. 101.

Di Pietro M.L. , Minacori R. Give 3,2 Abortions for 15 Years. M.L. Di Pietro, R. Minacori, op cit., p. 883.

It is admitted a 15% incidence of spontaneous abortions during the first trimester. Braunstein G.D. , Karowe W.G. , Gentry W.D. , Wade M.E. , “Subclinical Spontaneous Abortion,” Obstetrics and Gynecology, Vol. 50, No. 1 (Supplement), July 1977, pp. 41s–44s. D.K. Edmonds, K.S. Lindsay, J.F. Miller, E. Williamson, P.J. Wood, “Early Embryonic Mortality in Women,” Fertility and Sterility, vol. 38, no. 3-4, September/October 1982, pp. 447-453.

Bayle B. , op cit., p. 394.

McLaren A. , “Genetics of the Embryo,” in Bertanozzi V. , Fasella P. , Klepsch A eds. «Human Embryos and Research» Proceedings of the European Bioethics Conference in Mainz, 7-9 November 1988, Campus Verlag, Franfurt/New York, 1990, pp. 42-53.

Ford N.M. , When Did I begin? Conception of the Human Individual in History, Philosophy and Science, (Cambridge: Cambridge University Press, 1988). For the critic: see A. Fisher, “Individuogenesis and a Recent Book by Fr. Norman Ford,” Anthropotes, vol. 7, no. 2, Dicembre 1991, pp. 199-244.

For the philosophical discussion of the argument, see: Caspar Ph ., “Individuation Génétique et Gemellité: L'Objection des Jumeaux Monozygotes,” Ethique-la vie en Question, Printemps 1992, no. 4, pp. 81–90.

cf. Billings J.J. , “When Did I Begin” by Norman M. Ford. DSDB, Cambridge University Press,” Anthropotes, Vol. 5, No. 1, Maggio 1989, pp. 119–127. A. Serra, R. Colombo, “Identity and Status of the Human Embryo: The Contribution of Biology,” in De Dios Vial Correa J. , Sgreccia E. eds., «Identity and Statute of human embryo» Proceedings of Third Assembly of the Pontifical Academy for Life, Vatican City, February 14-16 1997, Libreria Editrice Vaticana, 1998, pp. 128-177.

Ward Kischer C. , “Human Development and Reconsideration of Ensoulment,” Linacre Quarterly, vol. 60, no 1, pp. 57–63. Ph. Caspar, “La Problématique de L'Animation de L'Embryon,” Nouvelle Revue Théologique, vol. 113, 1991, pp. 3-24.

Pangallo M. , “Actus Essendi Tomistico e Spiritualità Dell'Anima, Medicina e Morale, 1984/2, pp. 407–414. G. Cottier, «Scritti di Etica», Ed. Piemme, Casale Monferrato, 1994, pp. 295-297.

Lincoln D.W. , “Human Contraception: Development of New Scientific Opportunities,” Journal of Reproduction and Fertility, supplement 45, 1992, pp. 175–92, in partic. 175-177.

Andersch B. , Milsom I. , “Contraception and Pregnancy Among Young Women in an Urban Swedish Population,” Contraception, Vol. 26, No. 3, September 1982, pp. 211–219. I. Milsom, G. Sundell, B. Andersch, “A Longitudinal Study of Contraception and Pregnancy Outcome in a Representative Sample of Young Swedish Women,” Contraception, vol. 43, no 2, February 1991, pp. 111-119.

A-L Kosunien E. , Rimpela M.K. , “Towards Regional Equality in Family Planning: Teenage Pregnancies and Abortions in Finland from 1976 to 1993,” Acta Obstetricia et Gynecologica Scandinavica, Vol. 75, No. 6, July 1996, pp. 540–547.

The authors of this paper comment that way their data (p, 545): “It is possible that better availability of contraception tends to make attitudes toward early childbirth more negative, causing an increase in the proportion of those who chose abortion.”

Sidenius K. , Rasmussen N.K. , “Contraceptive Practice Among Abortion-Seeking Adolescents,” Acta Obstetricia et Gynecologica Scandinavica, supplement 116, 1983, no. 11, p. 14.

Etats-Unis: la contraception favorise l'avortement, Trans VIE-mag, no 99, 30 novembre 1996, p. 3, Lancet 17/8/1996.

Pearson V.A.H. , Owen M.R. , Phillips D.R. , Pereira Gray D.J. , Marshall M.N. , “Pregnant Teenagers’ Knowledge and Use of Emergency Contraception,” British Medical Journal, Vol. 310, No. 6995, 24 June 1995, p. 1644.

Williams E.S. , “Pregnant Teenagers and Contraception. Contraceptive Failure May Be a Major Factor in Teenage Pregnancy,” (letter), British Medical Journal, Vol. 311, No. 7008, 23 September 1995, pp. 806–807.

There were 586,760 induced abortions reported in the USA in 1972; 988,267 in 1976; 1,297,606 in 1980; 1,328,570 in 1988; 1,388,577 in 1991; 1,330,414 in 1993. “Abortion Surveillance: Preliminary Data - United States, 1994,” Journal of the American Medical Association, vol. 277, no. 4, January 22/29 1997, p. 284. “Abortion Surveillance: Preliminary Data - United States, 1993, Morbidity and Mortality Weekly Report, vol 45, no.11, March 22, 1996, pp. 235-238. “Abortion Surveillance: Preliminary Data - United States, 1994, Morbidity and Mortality Weekly Report, 1997, vol 45, no. 51-52, pp. 1123-1127. Morbidity and Mortality Weekly Report, 1997, 45; 1123-1127.

Clarke M. , “Fertility and Legal Abortion in England and Wales: Performance Indicators for Family Planning Services,” British Medical Journal, Vol. 297, No. 6652, 10 October 1988, pp. 832–833.

Nau J.Y. , “Le Nombre des Interruptions Volontaires de Grossesse ne Cesse de Diminuer,” Le Monde, Mercredi 11 juin 1997, p. 9.

Journal International de Bioéthique, vol. 7, no. 2, 1996, p. 135.

Nau J.Y. , op cit.

Rhonheimer M. , “Contraccezione, Mentalità Contrccettiva e Cultura Dell'aborto: Valutazioni e Connessioni,” in Sgreccia E. , Luca R. eds., «Commento Interdisciplinare alla “Evangelium Vitae”» Pontificia Accademia per la Vita, Libereria Editrice Vatican, 1997, pp. 435–452.

Rhonheimer M. , op ict., p. 445.

Hingorani V. , Kinra G. , Sarker B. , “Menstrual Regulation - Surgical or Medical,” in Recent Advances in Reproduction and Regulation of Fertility, Talwar G.P. ed., Elsevier/North-Holland Biomedical Press, Amsterdam-New York-Oxford, 1979, pp. 545–557.

Sylvestre L. , Dubois C. , Renault M. , Rezvani Y. , Baulieu E.E. , Ulmann A. , “Voluntary Interruption of Pregnancy with Mifepristone (RU-486) and a Prostaglandin Analogue. A Large-Scale French Experience,” New England Journal of Medicine, Vol. 322, No. 10, March 8, 1990, pp. 645–648.

Baulieu E.E. , “The Combined Use of Prostaglandin and Antiprogestin in Human Fertility Control,” European Journal of Obstetrics and Gynecology and Reproductive Biology, Vol. 65, No. 1, March 1996, pp. 115–119.

Capella A , Navaretta V. , Giacchi E. , “Il Metodo della Ovulazione Billings: Dati e Valutazioni Sullo Studio Multicentrico dell'Organizzazione Mondiale della Sanità,” Medicina e Morale, Vol. 32 no. 4, Ottobre-Decembre 1982, pp. 371–387. J.J. Brown, L.F. Blackwell, J.J. Billings, B. Conway, R.I. Cox, G. Garrett, J. Holmes, M.A. Smith, Natural Family Planning, in Shan Ratnam S. , Teoh Eng-Soon , Su-Min Lim Ng , eds., “Contraception”, Advances in Fertility and Sterility Series, vol. 6, The Proceedings of the 12th World Congress on Fertility and Sterility, Singapore, October 1986, The Parthenon Publishing Group, Casterton Hall, Carnforth, Lancs, UK, 1987, pp. 31-38. J.J. Brown, L.F. Blackwell, J.J. Billings, B. Conway, R.I. Cox, G. Garrett, J. Holmes, M.A. Smith, Natural Family Planning, American Journal of Obstetrics and Gynecology, vol. 157, no. 4, October 1987, part 2, pp. 1082-1089. Indian Council of Medical Research Task Force on Natural Family Planning, “Field Trial of Billings Ovulation Method of Natural Family Planning,” Contraception, vol. 53, no. 2, February 1996, pp. 69-74. R.E.J. Ryder, “‘Natural Family Planning’: Effective Birth Control Supported by the Catholic Church,” British Medical Journal, vol. 307, no. 6906, Saturday, 18 September 1993, pp. 723-726. H. von Hertzen, C. d'Arcangues, P.F.A. Van Look, “Methods for the Natural Regulation of Fertility,” in Annual Technical Report 1995, HRP Special Programme of Research, Development and Research Training in Human Reproduction, World Health Organization, Geneva, 1996, pp. 103-116.