Approximately 10% of women undergoing induced abortion suffer from immediate complications, of which one-fifth (2%) were considered major.  However the majority of complications take time to develop and will not be apparent for days, months or even years. Major risks and complications of abortion are described, with citations to the medical literature, below.
According to the best record based study of deaths following pregnancy and abortion, a 1997 government funded study in Finland, women who abort are approximately four times more likely to die in the following year than women who carry their pregnancies to term. In addition, women who carry to term are only half as likely to die as women who were not pregnant.  (Click here for more details on this important study.)
The Finland researchers found that compared to women who carried to term, women who aborted in the year prior to their deaths were 60 percent more likely to die of natural causes, seven times more likely to die of suicide, four times more likely to die of injuries related to accidents, and 14 times more likely to die from homicide.
Researchers believe the higher rate of deaths related to accidents and homicide may be linked to higher rates of suicidal or risk-taking behavior.  (Click here for details on the latest research regarding abortion associated deaths.)
The leading causes of abortion related maternal deaths within a week of the surgery are hemorrhage, infection, embolism, anesthesia, and undiagnosed ectopic pregnancies. Legal abortion is reported as the fifth leading cause of maternal death in the United States, though in fact it is recognized that most abortion-related deaths are not officially reported as such.  (Click here for more details on the underreporting of abortion related deaths in the U.S.)
Two studies of the entire population of women in Denmark published in 2012 have shown similar results. The first found that the risk of death following abortion remains higher in each of the first ten years following the abortion. The second found that the risk of death increases with each abortion, 45% after one abortion, 114% after two abortions, and 192 percent after three or more abortions.
For a complete review of the literature see Deaths associated with abortion compared to childbirth: a review of new and old data and the medical and legal implications (2004).
CERVICAL, OVARIAN, AND LIVER CANCER:
Women with a history of one abortion face a 2.3 times higher risk of having cervical cancer, compared to women with no history of abortion. Women with two or more abortions face a 4.92 relative risk. Similar elevated risks of subsequent ovarian and liver cancer have also been linked to single and multiple abortions. These increased cancer rates for post-aborted women may be linked to the unnatural disruption of the hormonal changes which accompany pregnancy and untreated cervical damage or to increased stress and the negative impact of stress on the immune system. 
Between 2 and 3% of all abortion patients may suffer perforation of their uterus, yet most of these injuries will remain undiagnosed and untreated unless laparoscopic visualization is performed.  Such an examination may be useful when beginning an abortion malpractice suit. The risk of uterine perforation is increased for women who have previously given birth and for those who receive general anesthesia at the time of the abortion.  Uterine damage may result in complications in later pregnancies and may eventually evolve into problems which require a hysterectomy, which itself may result in a number of additional complications and injuries including osteoporosis.
Significant cervical lacerations requiring sutures occur in at least one percent of first trimester abortions. Lesser lacerations, or micro fractures, which would normally not be treated may also result in long term reproductive damage. Latent post-abortion cervical damage may result in subsequent cervical incompetence, premature delivery, and complications of labor. The risk of cervical damage is greater for teenagers, for second trimester abortions, and when practitioners fail to use laminaria for dilation of the cervix. 
Abortion increases the risk of placenta previa in later pregnancies (a life threatening condition for both the mother and her wanted pregnancy) by seven to fifteen fold. Abnormal development of the placenta due to uterine damage increases the risk of fetal malformation, perinatal death, and excessive bleeding during labor. 
SUBSEQUENT PRE-TERM DELIVERIES AND OTHER COMPLICATIONS OF LABOR:
Women who had one, two, or more previous induced abortions are, respectively, 1.89, 2.66, or 2.03 times more likely to have a subsequent pre-term delivery, compared to women who carry to term. Prior induced abortion not only increased the risk of premature delivery, it also increased the risk of delayed delivery. Women who had one, two, or more induced abortions are, respectively, 1.89, 2.61, and 2.23 times more likely to have a post-term delivery (over 42 weeks).  Pre-term delivery increases the risk of neonatal death and handicaps.
PRETERM BIRTH/HANDICAPPED NEWBORNS IN LATER PREGNANCIES:
Abortion is associated with cervical and uterine damage which may increase the risk of premature delivery, complications of labor and abnormal development of the placenta in later pregnancies. These reproductive complications are the leading causes of handicaps among newborns. 
Three “study of studies” papers (systematic reviews), have found that prior induced abortions significantly elevate the risk of having a premature birth in the future. One of the authors, Dr. Prakesh Shah of the University of Toronto, had his study published in the prestigious British Journal of Obstetrics & Gynaecology. Dr. Shah reported that one prior induced abortion multiplies premature birth risk by 1.36, but more than one prior induced abortion almost doubles the risk (1.93 times the risk). 
These reviews confirm the finding by the U.S. Institute of Medicine that one of fourteen “Immutable Medical Risk Factors Associated with Preterm Birth” is “prior first trimester induced abortion.” 
Abortion is significantly related to an increased risk of subsequent ectopic pregnancies. Ectopic pregnancies, in turn, are life threatening and may result in reduced fertility. 
PELVIC INFLAMMATORY DISEASE (PID):
PID is a potentially life threatening disease which can lead to an increased risk of ectopic pregnancy and reduced fertility. Of patients who have a chlamydia infection at the time of the abortion, 23% will develop PID within 4 weeks. Studies have found that 20 to 27% of patients seeking abortion have a chlamydia infection. Approximately 5% of patients who are not infected by chlamydia develop PID within 4 weeks after a first trimester abortion. It is therefore reasonable to expect that abortion providers should screen for and treat such infections prior to an abortion. 
Endometritis is a post-abortion risk for all women, but especially for teenagers, who are 2.5 times more likely than women 20-29 to acquire endometritis following abortion. 
Approximately 10% of women undergoing elective abortion will suffer immediate complications, of which approximately one-fifth (2%) are considered life threatening. The nine most common major complications which can occur at the time of an abortion are: infection, excessive bleeding, embolism, ripping or perforation of the uterus, anesthesia complications, convulsions, hemorrhage, cervical injury, and endotoxic shock. The most common “minor” complications include: infection, bleeding, fever, second degree burns, chronic abdominal pain, vomiting, gastro-intestinal disturbances, and Rh sensitization. 
INCREASED RISKS FOR WOMEN SEEKING MULTIPLE ABORTIONS:
In general, most of the studies cited above reflect risk factors for women who undergo a single abortion. These same studies show that women who have multiple abortions face a much greater risk of experiencing these complications. This point is especially noteworthy since approximately 45% of all abortions are for repeat aborters.
LOWER GENERAL HEALTH:
In a survey of 1428 women researchers found that pregnancy loss, and particularly losses due to induced abortion, was significantly associated with an overall lower health. Multiple abortions correlated to an even lower evaluation of “present health.” While miscarriage was detrimental to health, abortion was found to have a greater correlation to poor health. These findings support previous research which reported that during the year following an abortion women visited their family doctors 80% more for all reasons and 180% more for psychosocial reasons. The authors also found that “if a partner is present and not supportive, the miscarriage rate is more than double and the abortion rate is four times greater than if he is present and supportive. If the partner is absent the abortion rate is six times greater.” 
This finding is supported by a 1984 study that examined the amount of health care sought by women during a year before and a year after their induced abortions. The researchers found that on average, there was an 80 percent increase in the number of doctor visits and a 180 percent increase in doctor visits for psychosocial reasons after abortion. 
INCREASED RISK FOR CONTRIBUTING HEALTH RISK FACTORS:
Abortion is significantly linked to behavioral changes such as promiscuity, smoking, drug abuse, and eating disorders which all contribute to increased risks of health problems. For example, promiscuity and abortion are each linked to increased rates of PID and ectopic pregnancies. Which contributes most is unclear, but apportionment may be irrelevant if the promiscuity is itself a reaction to post- abortion trauma or loss of self esteem.
INCREASED RISKS FOR TEENAGERS:
Teenagers, who account for about 30 percent of all abortions, are also at much high risk of suffering many abortion related complications. This is true of both immediate complications, and of long-term reproductive damage. 
See this link for Psychological Complications
1. Detrimental Effects of Abortion: An Annotated Bibliography with Commentary (Third Edition) is the most complete review of medical studies relevant to abortion. It includes brief summaries of major finding drawn from medical and psychology journal articles, books, and related materials, divided into major categories of relevant injuries. An online version of the bibliography can be found at www.AbortionRisks.com2. Kaunitz, “Causes of Maternal Mortality in the United States,” Obstetrics and Gynecology, 65(5) May 1985.3. H.L. Howe, et al., “Early Abortion and Breast Cancer Risk Among Women Under Age 40,” International Journal of Epidemiology 18(2):300-304 (1989); L.I. Remennick, “Induced Abortion as A Cancer Risk Factor: A Review of Epidemiological Evidence,” Journal of Epidemiological Community Health, (1990); M.C. Pike, “Oral Contraceptive Use and Early Abortion as Risk Factors for Breast Cancer in Young Women,” British Journal of Cancer 43:72 (1981).4. M-G, Le, et al., “Oral Contraceptive Use and Breast or Cervical Cancer: Preliminary Results of a French Case- Control Study, Hormones and Sexual Factors in Human Cancer Etiology, ed. JP Wolff, et al., Excerpta Medica: New York (1984) pp.139-147; F. Parazzini, et al., “Reproductive Factors and the Risk of Invasive and Intraepithelial Cervical Neoplasia,” British Journal of Cancer, 59:805-809 (1989); H.L. Stewart, et al., “Epidemiology of Cancers of the Uterine Cervix and Corpus, Breast and Ovary in Israel and New York City,” Journal of the National Cancer Institute 37(1):1-96; I. Fujimoto, et al., “Epidemiologic Study of Carcinoma in Situ of the Cervix,” Journal of Reproductive Medicine 30(7):535 (July 1985); N. Weiss, “Events of Reproductive Life and the Incidence of Epithelial Ovarian Cancer,” Am. J. of Epidemiology, 117(2):128-139 (1983); V. Beral, et al., “Does Pregnancy Protect Against Ovarian Cancer,” The Lancet, May 20, 1978, pp. 1083-1087; C. LaVecchia, et al., “Reproductive Factors and the Risk of Hepatocellular Carcinoma in Women,” International Journal of Cancer, 52:351, 1992.
5. S. Kaali, et al., “The Frequency and Management of Uterine Perforations During First-Trimester Abortions,” Am. J. Obstetrics and Gynecology 161:406-408, August 1989; M. White, “A Case-Control Study of Uterine Perforations documented at Laparoscopy,” Am. J. Obstetrics and Gynecology 129:623 (1977).
6. D. Grimes, et al., “Prevention of uterine perforation During Curettage Abortion,” JAMA, 251:2108-2111 (1984); D. Grimes, et al.,”Local versus General Anesthesia: Which is Safer For Performing Suction Abortions?” Am. J. of Obstetrics and Gynecology, 135:1030 (1979).
7. K. Schulz, et al., “Measures to Prevent Cervical Injuries During Suction Curettage Abortion,” The Lancet, May 28, 1983, pp 1182-1184; W. Cates, “The Risks Associated with Teenage Abortion,” New England Journal of Medicine, 309(11):612-624; R. Castadot, “Pregnancy Termination: Techniques, Risks, and Complications and Their Management,” Fertility and Sterility, 45(1):5-16 (1986).
8. Barrett, et al., “Induced Abortion: A Risk Factor for Placenta Previa”, American Journal of Ob&Gyn. 141:7 (1981).
9. Hogue, Cates and Tietze, “Impact of Vacuum Aspiration Abortion on Future Childbearing: A Review”, Family Planning Perspectives (May-June 1983),vol.15, no.3.. Jacobsson B, Hagberg G, Hagberg B, Ladfors L, Niklasson A, Hagberg A. Cerebral Palsy in preterm infants: a population-based case-control study of antenatal and intrapartal risk factors. Acta Paediatrica 2002;91:946-951. Calhoun BC, Shadigian E, Rooney B. Cost consequences of induced abortion as an attributable risk for preterm birth and informed consent. J Reprod Med 2007;52:929-939.
10. Daling,et.al., “Ectopic Pregnancy in Relation to Previous Induced Abortion”, JAMA, 253(7):1005-1008 (Feb. 15, 1985); Levin, et.al., “Ectopic Pregnancy and Prior Induced Abortion”, American Journal of Public Health (1982), vol.72,p253; C.S. Chung, “Induced Abortion and Ectopic Pregnancy in Subsequent Pregnancies,” American Journal of Epidemiology 115(6):879-887 (1982)
11. T. Radberg, et al., “Chlamydia Trachomatis in Relation to Infections Following First Trimester Abortions,” Acta Obstricia Gynoecological (Supp. 93), 54:478 (1980); L. Westergaard, “Significance of Cervical Chlamydia Trachomatis Infection in Post-abortal Pelvic Inflammatory Disease,” Obstetrics and Gynecology, 60(3):322-325, (1982); M. Chacko, et al., “Chlamydia Trachomatosis Infection in Sexually Active Adolescents: Prevalence and Risk Factors,” Pediatrics, 73(6), (1984); M. Barbacci, et al., “Post- Abortal Endometritis and Isolation of Chlamydia Trachomatis,” Obstetrics and Gynecology 68(5):668-690, (1986); S. Duthrie, et al., “Morbidity After Termination of Pregnancy in First-Trimester,” Genitourinary Medicine 63(3):182-187, (1987).
12. Burkman, et al., “Morbidity Risk Among Young Adolescents Undergoing Elective Abortion” Contraception, 30:99-105 (1984); “Post-Abortal Endometritis and Isolation of Chlamydia Trachomatis,” Obstetrics and Gynecology 68(5):668- 690, (1986)
13. Frank, et.al., “Induced Abortion Operations and Their Early Sequelae”, Journal of the Royal College of General Practitioners (April 1985),35(73):175-180; Grimes DA, Cates W Jr. Abortion: Methods and complications. In: Hafez ESE, ed. Human reproduction: Conception and contraception (2nd ed). Hagerstown, Maryland: Harper and Row, 1980:796‑813.; M.A. Freedman, “Comparison of complication rates in first trimester abortions performed by physician assistants and physicians,” Am. J. Public Health, 76(5):550- 554 (1986).
14. Wadhera, “Legal Abortion Among Teens, 1974-1978”, Canadian Medical Association Journal, 122:1386-1389,(June 1980).
15. Ney, et.al., “The Effects of Pregnancy Loss on Women’s Health,” Soc. Sci. Med. 48(9):1193-1200, 1994; Badgley, Caron, & Powell, Report of the Committee on the Operation of the Abortion Law, Supply and Services, Ottawa, 1977: 319-321.
16. Gissler, M., et. al., “Pregnancy-associated deaths in Finland 1987-1994 — definition problems and benefits of record linkage,” Acta Obsetricia et Gynecolgica Scandinavica 76:651-657 (1997).
17. Zhou, Weijin, et. al., “Induced Abortion and Subsequent Pregnancy Duration,” Obstetrics & Gynecology 94(6):948-953 (Dec. 1999). Klemetti R, Gissler M, Niinimäki M, Hemminki E. Birth outcomes after induced abortion: a nationwide register-based study of first births in Finland. Hum Reprod 2012 Aug 29. [Epub ahead of print]. Rooney B, Calhoun BC. Induced Abortion and Risk of Later Premature Births. Journal American Physicians & Surgeons 2003;8(2):46-49 Bhattacharya S, Lowit A, Bhattacharya S, Raja EA. -et al. Reproductive outcomes following induced abortion: a national register-based study in Scotland. BMJ OPEN Summer 2012. Swingle HM, Colaizy TT, Zimmerman MB, et al Abortion and the risk of subsequent preterm birth: a systematic review and meta-analysis. J Reproductive Med 2009;54:95-108.
18. D. Berkeley, P.L. Humphreys, and D. Davidson, “Demands Made on General Practice by Women Before and After an Abortion,” J. R. Coll. Gen. Pract. 34:310-315, 1984.
19. Frank, et.al., “Induced Abortion Operations and Their Early Sequelae”, Journal of the Royal College of General Practitioners (April 1985), vol.35,no.73,pp175-180. and Grimes and Cates, “Abortion: Methods and Complications”, Human Reproduction, 2nd ed., 796-813.
20. See P.S. Shah and J. Zao, “Induced termination of pregnancy and low birthweight and preterm birth: a systematic review and meta-analysis,” BJOG 116(11): 1425-1442 (2009); H.M. Swingle et. al., “Abortion and the Risk of Subsequent Preterm Birth: A Systematic Review and Meta-Analysis,” Journal of Reproductive Medicine 54:95-108 (2009); and Ankum WM, Lemmers M, Vershoor MAC, Hooker AB, Opmeer BC. Does dilation and curettage (D & C) increase the risk of preterm birth in subsequent pregnancies? A systematic review and meta-analysis.
21. Richard E. Behrman and Adrienne Stith Butler (eds.), Preterm Birth: Causes, Consequences and Prevention (Washington, DC: The National Academies Press, 2007) 625.
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