Early Preterm Birth (under 32 weeks gestation) and Cerebral Palsy in Subsequent Pregnancies after Abortion

Martha Shuping
April 17, 2007
Reproduced with Permission

Early preterm infants, those born before 32.0 weeks gestation, comprise only 15% of the premature population, but experience 80% of the neonatal deaths.1 Early preterm infants also constitute a majority of those with serious disabilities, including mental retardation, epilepsy, blindness, deafness, lung infections, and cerebral palsy.2

Extremely early premature birth, less than 28 weeks gestation, is even more serious, with the highest risk of complications for the infant. For example, the risk of cerebral palsy in extremely early preterm birth is "about 38 times higher than in the overall population of newborns."3

Rooney and Calhoun found that very large studies demonstrated that the risk of an extremely premature birth doubled after two prior induced abortions. They also found that women who had four or more induced abortions had nine times the risk of extremely premature birth, "an increase of 800 percent."4

The largest European study of abortion and preterm birth was that of Maritius et al. in 1998 which included 106,345 German subjects.5 This study showed that with one prior induced abortion, the odds ratio for having an early preterm birth in future was 2.5; if two past abortions, the odds ratio was 5.2; for more than two prior abortions, an odds ratio of 8.0. This study showed induced abortion is clearly associated with an increased risk of preterm birth of less than 37 weeks, but that the association was even stronger for the risk of early preterm birth. All the results were statistically significant. The Maritius study demonstrates a "dose response" effect in which multiple abortions are associated with higher risk.

Another important study was that of Lumley in Victoria, Australia in 1993, involving 121,305 births.6 She examined the risk of preterm birth (32-36 weeks), early preterm birth (28-31 weeks) and extremely early preterm birth (20-27 weeks gestation) in relation to numbers of induced abortions. She found induced abortion was associated with each of these three categories of early birth, but the relative risk was the most increased ("striking") in regard to the earliest gestations.

Also, she found a "dose response effect," showing the relative risk of an early birth increased steadily with increasing numbers of abortions. Thus, a woman with one induced abortion had a relative risk of 1.6 for having an extremely early preterm birth (20-27 weeks), but a woman with 2 past abortions had a relative risk of 2.5, and a woman with three or more abortions had a relative risk of 5.6. She said the association was "most unlikely to be explained by confounding factors."

Rooney and Calhoun identify several possible mechanisms by which abortion causes an increased risk of premature birth. "An accepted risk of surgical induced abortion is incompetent cervix which is a premature birth risk factor."7 Other "risk factors for premature birth that may be increased by abortion include uterine adhesions [and] infection."8

Rooney and Calhoun, citing Lumley 1998, state that "the evidence meets four of the criteria for determining causality," in that "the abortions preceded the premature births," that "the association is strong," that there is a dose-response relationship," and that "the association is plausible."9 Rooney and Calhoun further point out that one criterion for causality which could not be met in 1998 when Lumley’s paper was published, has since been met: "confirmation by a prospective study."10

"In the overall population of newborns, the risk of cerebral palsy is approximately 2-3 per 1,000 births."11 Thus it can be claimed that "induced abortion ... is directly responsible for many thousands of cases of cerebral palsy… that would otherwise not have occurred."12

What are the implications in regard to informed consent?

Thorp, Hartmann and Shadigian (2003), stated, based on their review of all large (more than 100 subjects) long term studies of abortion up to 2002: "We conclude that informed consent before induced abortion should include information about the subsequent risk of preterm delivery."13

Rooney and Calhoun14 (2003) point out, "As the liability costs for cerebral palsy are exceptionally high, induced abortion, particularly without very detailed informed consent, may carry an unsupportable legal liability. Courts may not require definitive proof of causation; the existence of a number of positive studies, in the absence of definitive refutation, may be sufficient reason to include discussion of a potential serious adverse effect in obtaining informed consent."

The author has consistently opposed abortion and continues to do so; however, a careful examination of the claims made in this submission should alert people of conscience on either side of this contentious issue to this significant issue which is well documented within the published literature. The author wishes to acknowledge the generous assistance of Dr. Byron C. Calhoun, M.D. and Brent Rooney, in the preparation of this submission.


1 Martin JA, Hamilton BE, Sutton PD, Ventura SJ, Menacker F, Munson ML. Births: Final data for 2002. National Vital Statistics Reports. 2002; 52(10). [Back]

2 Escobar GJ, Littenberg B, Petitti DB. Outcome among surviving very low birthweight infants; a meta-analysis. Arch Dis Child 1991; 66:204-211. [Back]

3 Rooney B and Calhoun C. Induced abortion and risk of later premature birth. Journal of American Physicians and Surgeons 2003; 8:(2)46-49 (Accessed March 4, 2007, from http://www.jpands.org/vol8no2/rooney.pdf), citing Escobar et al., op. cit. [Back]

4 Rooney B and Calhoun C. Induced abortion and risk of later premature birth. Journal of American Physicians and Surgeons 2003; 8:(2)46-49. [Back]

5 Martius JA, Steck T, Oehler MK, Wulf K-H. Risk factors associated with preterm (<37+0 weeks) and early preterm (<32+0 weeks): univariate and multi-variate analysis of 106,345 singleton births from 1994 statewide perinatal survey of Bavaria. Eur J Obstet Gynecol Reprod Biol 1998;80:183-189. [Back]

6 Lumley J. The epidemiology of preterm birth. Bailliere's Clin Obstet Gynecol. 1993;7(3):477-498. [Back]

7 Rooney and Calhoun, op. cit., citing Berkowitz GS, Papiernik E. Epidemiology of preterm birth. Epidemiol Rev 1993; 15:414-443. [Back]

8 Rooney and Calhoun, op. cit., citing Berkowitz et. al., op. cit.; Daling JR, Krohn MA, Miscarriage or termination in the immediately preceding pregnancy increases the risk of intraamniotic infection in the following pregnancy Am J Epidemiol 1992; 136:1013 SER Abstracts; Lumley J. The association between prior spontaneous abortion, prior induced abortion and preterm birth in first singleton births. Prenat Neonat Med 1998; 3:21-24. Muhlemann K, Germain M, Krohn M. Does an abortion increase the risk of intrapartum infection in the following pregnancy? Epidemiol 1996; 7:194-198; Ring-Cassidy E, Gentles I. Toronto, Woman's Health after Abortion. Toronto, Ontario: de Veber Institute; 2002. [Back]

9 Rooney and Calhoun, op. cit., citing Lumley J. The association between prior spontaneous abortion, prior induced abortion and preterm birth in first singleton births. Prenat NeonatMed 1998; 3:21-24. [Back]

10 Rooney and Calhoun, op. cit., citing Zhou W, Sorenson HT, Olsen J. Induced abortion and subsequent pregnancy duration. Obstet Gynecol 1999; 94:948-953. [Back]

11 Rooney and Calhoun, 2003, citing Smith, WS, Camfield C, and Camfield, P. Living with cerebral palsy and tube feeding: a population-based follow-up study. J Pediatr 1999; 135:307-310. [Back]

12 Rooney and Calhoun, op. cit., citing Ring-Cassidy and Gentles, Woman’s Health after Abortion. Toronto, Ontario: de Veber Institute; 2002. [Back]

13 Thorp JM, Hartmann KE, Shadigian EM. Long-term physical and psychological health consequences of induced abortion: review of the evidence, Obstet Gynecol Survey 2003; 58 (1): 67-79, (accessed March 4, 2007 from http://www.obgynsurvey.com) [Back]

14 Rooney and Calhoun, op. cit. [Back]