induced abortion and subsequent preterm birth evidence of risk association

8/7/2019 Induced Abortion and Subsequent Preterm Birth Evidence of Risk Association

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Induced Abortion and Subsequent Preterm Birth:

Evidence of Risk Association

Byron C. Calhoun, M.D., FACOG, FACS, MBAProfessor & Vice-Chair, Department of Obstetrics & Gynecology

West Virginia University-Charleston

U.S. Surgeon Generals Conference on the Prevention ofPreterm Birth

June 16 & 17, 2008


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The abstracts, referenced studies, and two papers contained in this document provideevidence of a causal link between surgical induced abortion (IA) and subsequent preterm

birth. One of the two papers at the conclusion of the document gives further considerationto this causal link with respect to both cost consequences and impact on informed

consent.

ABSTRACTS

The following abstracts represent six studies which demonstrate the strongest and most

significant risk association between IA and later preterm birth.

(1.) Lumley J. The epidemiology of preterm birth.Bailliere's Clin Obstet Gynecology.1993;7(3):477-498ABSTRACT

Secular trends in the prevalence of preterm birth and international comparisons of the rates of

preterm birth are difficult to interpret because of differences, both formal and informal, in the

registration of extremely preterm births. Accurate estimation of gestational age is another

problem in the measurement of preterm birth. Preterm birth is heterogeneous in several ways. It is

heterogeneous in terms of the extent to which the birth is preterm (20-27 weeks, 28-31 weeks or32-36 weeks of gestation); in whether the birth was elective or spontaneous; and among

spontaneous idiopathic preterm births, in whether there was preterm labour or premature rupture

of the membranes. Case-control study designs taking account of these subgroups have been a

recent feature of epidemiologic approaches. The classic social associations of preterm birth--low

socioeconomic status, extremes of maternal age, primiparity, being unmarried--apply to

extremely preterm and moderately preterm births as well as to the mildly preterm group. The

strength of these associations is small compared with factors in the prior reproductive history and

with medical and obstetric complications of the current pregnancy. Recent epidemiological

research activities have focused on the ways in which risk factors such as physical workload,

drugs and alcohol, lack of social support and infection might be mediating factors between

sociodemographic status and preterm birth. As Eastman (1947) pointed out almost 50 years ago,

'only when the factors causing prematurity are clearly understood can any intelligent attempt atprevention be made'. [References: 74]

(2.) Lumley J. The association between prior spontaneous abortion, prior inducedabortion and preterm birth in first singleton births.Prenat Neonat Med1998;3:21-24.DISCUSSION (in lieu of Abstract)

The evidence for and against a causal relationship between prior shortened pregnancies

and preterm birth is as follows. Selection bias into the study can be excluded since the data are

population-based with 99.6% of births captured in the data system. Measurement error of the

exposures cannot be totally excluded. Though the data have been validated against hospital

records there is likely to be incomplete reporting of prior induced abortions in hospital records.

Non-differential under-reporting would result in the relative risk being too low. Differential

under-reporting is which prior abortions were more completely ascertained when there was apreterm birth could have occurred but the timing of data collection on prior pregnancies is at the

first antenatal visit, before the outcome is known. Chance (random error) is unlikely since the

95% confidence intervals for the association with prior abortions do not include 1.00 .

Confounding is likely. Maternal age, marital status and the presence of a birth defect in

the index birth can be excluded since the associations in Figures 1 to 3 are still present at a similar

level in a restricted data stratum of married women, age 20-34 years, with no birth defect in the

index birth (unpublished data). Data on socioeconomic status, occupation, smoking, alcohol


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consumption and other substance use are not collected routinely. The strength of association of

these factors with preterm birth, however, is much smaller than the associations in Figures 1 to 3.

The association of abortions with preterm birth cannot be explained by gravidity because the

relative risks for prior births are different from prior pregnancies. Data on the gestation of the

prior abortions, indications, complications, and inter-pregnancy intervals are not available in the

routine perinatal data.

Termination of pregnancy has been legal under case interpretation of legislation since1969 and the procedure is covered by the federal government universal health insurance system

[4].

The data meet four of the criteria for causality. The temporal sequence is clear: the

abortions preceded the preterm birth. The association is a strong one. There is a dose-response

relationship: the greater the number of prior pregnancies the higher the relative risk. The

association is plausible: possible mechanisms exist which are outlined below. The other criteria

cannot be fully met a present: the study design (a retrospective cohort) is rated as moderate.

Reversibility of the exposure is not applicable to these exposures. No other papers have reported

an analysis stratified by gestation and by number of prior pregnancies so that the consistency of

the findings cannot be assessed.

One possible mechanism is that cervical instrumentation can facilitate the passage of

organisms into the upper part of the uterus, increasing the probability of inapparent infection andsubsequent preterm birth [5]. Another is the removal of the endometrium carries a small risk of

damaging the decidual stroma in such a way as to impair trophoblast invasion, migration and the

full transformation of the maternal spiral arteries [6].

(3.) Moreau C, Kaminski M, Ancel PY, Bouyer J, Escande B, et al. Previous inducedabortions and the risk of very preterm delivery: results of the EPIPAGE study.

British J Obstetrics Gynaecology 2005;112(4):430-437.ABSTRACT

Objectives: To evaluate the risk of very preterm birth (22-32 weeks of gestation) associated with

previous induced abortion according to the complications leading to very preterm delivery in

singletons. Design: Multicentre, case-control study (the French EPIPAGE study). Setting:

Regionally defined population of births in France. Sample: The sample consisted of 1943 very

preterm live-born singletons (< 33 weeks of gestation), 276 moderate preterm live-born

singletons (33-34 weeks) and 618 unmatched full-term controls (39-40 weeks). Methods: Data

from the EPIPAGE study were analysed using polytomous logistic regression models to control

for social and demographic characteristics, lifestyle habits during pregnancy and obstetric history.

The main mechanisms of preterm delivery were classified as gestational hypertension, antepartum

haemorrhage, fetal growth restriction, premature rupture of membranes, idiopathic preterm labor

and other causes. Main Outcome Measures: Odds ratios for very preterm birth by gestational

age and by pregnancy complications leading to preterm delivery associated with a history of

induced abortion. Results: Women with a history of induced abortion were at higher risk of very

preterm delivery than those with no such history (OR + 1.5, 95% CI 1.1-2.0); the risk was even

higher for extremely preterm deliveries (< 28 weeks). The association between previous induced

abortion and very preterm delivery varied according to the main complications leading to very preterm delivery. A history of induced abortion was associated with an increased risk of

premature rupture of the membranes, antepartum haemorrhage (not in association with

hypertension) and idiopathic spontaneous preterm labour that occur at very small gestational ages

(< 28 weeks). Conversely, no association was found between induced abortion and very preterm

delivery due to hypertension. Conclusion: Previous induced abortion was associated with an

increased risk of very preterm delivery. The strength of the association increased with decreasing

gestational age.


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(4.) Stang P, Hammond AO, Bauman P. Induced Abortion Increases the Risk of VeryPreterm Delivery; Results from a Large Perinatal Database.Fertility Sterility Sept

2005;S159ABSTRACT

Objective: 49% of pregnancies among American women are unintended; 1/2 of these are

terminated by abortion. In 2000, 1.31 million abortions took place in the USA. There has been

debate over the impact of induced abortions (VTP) on future pregnancy outcome, particularly the

risk of very preterm birth (95thpercentile, maternal age


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degree of prematurity. However, modelsbased on maternal and biochemical data perform poorly

as a screeningtest for any degree of spontaneous preterm birth.

(6.) Levin AA, Schoenbaum SC, Monson RR, Stubblefield PG, Ryan JA. Association ofInduced Abortion with Subsequent Pregnancy Loss.JAMA 1980;243(24):2495-2499ABSTRACT

We compared prior pregnancy histories of two groups of multigravidas--240 women having a

pregnancy loss up to 28 weeks' gestation and 1,072 women having a term delivery. Women who

had had two or more prior induced abortions had a twofold to threefold increase in risk of first-

trimester spontaneous abortion, loss between 14 to 19 and 20 to 27 weeks. The increased risk was

present for women who had legal induced abortions since 1973. It was not explained by smoking

status, history of prior spontaneous loss, prior abortion method, or degree of cervical dilatation.

No increase in risk of pregnancy loss was detected among women with a single prior induced

abortion. We conclude that multiple induced abortions do increase the risk of subsequent

pregnancy losses up to 28 weeks' gestation.

BIBLIOGRAPHY

The following list provides 51 peer-reviewed studies demonstrating a significant riskbetween IA and subsequent preterm birth since 1989. This list is not exhaustive.

* studies that included spontaneous and induced abortions but did not report preterm birth and

low birth weight (LBW) risk separately for each.

+ studies that found a dose response effect (signifying an increased risk of preterm birth

following increased number of induced abortions.)

1990s

+A01 Vasso L-K, Chryssa T-B, Golding J. Previous obstetric history and subsequentpreterm delivery in Greece.European J Obstetrics& Gynecology ReproductiveBiology 1990;37:99-109.

A02 Li YJ, Zhou YS. Study of factors associated with preterm delivery.Zhongjua Liu

Xing Bing Xue Za Chi. Aug 1990;11(4):229-234.

A03 Harger JH, Hsing AW, Tuomala RE, Gibbs RS, Mead PG et al. Risk factors forpreterm premature rupture of fetal membranes: A multicenter case-control study.

Am J Obstet Gynec 1990;163:130-137.

A04 McGregor JA, French J, Richter R. Antenatal microbiologic and maternal riskfactors associated with prematurity.Amer J Obstet Gynecol 1990;163:1465-1473

A05 Pickering RM, Deeks JJ. Risks of Delivery during 20th to the 36th Week of

Gestation.Intl. J Epidemiology 1991;20:456-466.

*+A06 Zhang J, Savitz DA. Preterm Birth Subtypes among Blacks and Whites.Epidemiology 1992;3:428-433.


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*A07 Michielutte R, Ernest JM, Moore ML, Meis PJ, Sharp PC, Wells HB, Buescher

PA. A Comparison of Risk Assessment Models for Term and Preterm LowBirthweight.Preventive Medicine 1992;21:98-109.

A08 Gong JH. Preterm delivery and its risk factors. Zhounghua Fu ChanKe Za Chi Jan. 1992;27(1):22-24

A09 Mandelson MT, Maden CP, Daling JR. Low Birth Weight in Relation MultipleInduced Abortions.Am J Public Health 1992;82;391-394

+A10 Lumley J. The epidemiology of preterm birth. Bailliere's Clin Obstet Gynecology.

1993;7(3):477-498

A11 Algert C, Roberts C, Adelson P, Frammer M. Low birth weight in New SouthWales, 1987: a Population-Based Study. Aust New ZealandJ Obstet Gynaecol

1993;33:243-248.

A12 Ekwo EE, Grusslink CA, Moawad A. Previous pregnancy outcomes andsubsequent risk of premature rupture of amniotic sac membranes.Brit J Obstet

Gynecol 1993;100(6):536-541.

A13 Lekea-Karanika V, Tzoumaka-Bangoula C. Past obstetric history of the motherand its association with low birth weight of a subseaquent child: a population-

based study. Paediatric Perinat Epidemiol 1994;8:173-187

A14 Guinn D, Goldenberg RL, Hauth JC, Andrews WA, Thom E, Romero R. Riskfactors for the development of preterm premature rupture of membranes after

arrest of preterm labor. AJOG 1995;173(4):1310-1315.

*A15 Hillier SL, Nugent RP, Eschenbach DA, Krohn MA,et al. Association BetweenBacterial Vaginosis And Preterm Delivery Of A Low-Birth-Weight Infant.NEJM

1995;333:1737-1742.

A16 Khalil AK, El-Amrawy SM, Ibrahim AG, et al. Pattern of growth anddevelopment of premature children at the age of two and three years in

Alexandria, Egypt.Eastern Mediterranean Health Journal 1995;1(2):186-193.

A17 Meis PJ, Michielutte R, Peters TJ, Wells HB. Factors associated with pretermbirth in Cardiff, Wales. Amer J Obstet Gynecol1995;173:590-596.

+A18 Lang JM, Lieberman E, Cohen A. A Comparison of Risk Factors for Preterm

Labor and Term Small-for-Gestational-Age Birth.Epidemiology 1996;7:369-376.

*A19 Hagan R, Benninger H, Chiffings D. Evans S, French H. Very preterm birth - aregional study. Part 1: Maternal and obstetric factors. BJOG 1996;103:230-238.


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A20 Chie-Pein Chen, Kuo-Gon Wang, Yuh-Cheng Yang, Lai-Chu See. Risk factors

for preterm birth in an upper middle class Chinese population. Eur J ObstetGynecol Reprod Bio 1996;70(1):53-59.

A21 Jacobsen G, Schei B, Bakketeig LS. Prepregnant reproductive risk and subsequentbirth outcome among Scandinavian parous women. NorskEpidemiol1997;7(1):33-39.

+A22 Lumley J. The association between prior spontaneous abortion, prior induced

abortion and preterm birth in first singleton births.Prenat Neonat Med1998;3:21-24.

+A23 Martius JA, Steck T, Oehler MK, Wulf K-H. Risk factors associated with preterm

(


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comparisons betweeen spontaneous prematurity and induced labor; results fromthe National Perinatal Survey 1995. J Gynecol Obstet Bio Reprod(Paris) Feb

2000;29(1);55-65.

*A31 Gardosi J, Francis A. Early Pregnancy predictors of preterm birth: the role

of a prolonged menstruation-conception interval. BJOG 2000;107(2):228-237.

A32 Bettiol H, Rona RJ, Chin S, Goldani M, Barberi M. Risk Factors Associated

with preterm births in Southeast Brazil: a comparison of two birth cohortsborn 15 years apart. Paediatric Perinatal Epidemiol 2000;14(1):30-38.

+A33 Henriet L, Kaminski M. Impact of induced abortions on subsequent pregnancy

outcome: the 1995 French national perinatal survey. British JObstetricsGynaecology 2001;108:1036-1042.

A34 Letamo G, Majelantle RG. Factors Influencing Low Birth Weight and Prematurity

in Botswana. J Biosoc Sci 2001;33(3):391-403.

A35 Grimmer I, Buhrer C, Dudenhausen JW. Preconceptional factors associated withvery low birth weight delivery: a case-control study. BMC Public Health 2002;

2:10 [Germany].

A36 Balaka B, Boeta S, Aghere AD, Boko K, Kessie K, Assimadi K. Risk factorsassociated with prematurity at the University of Lme, Togo. Bull Soc Pathol Exot

Nov 2002;95(4):280-283.

A37 Han WH, Chen LM, Li CY. Incidences of and Predictors for Preterm Births andLow Birth Weight Infants in Taiwan. Chinese ElectronicPeriodical Services

2003:131-141.

A38 Reime B, Schuecking BA, Wenzlaff P. Perinatal outcomes of teenagepregnancies according to gravidity and obstetric history.Annals of Epidemiology

2004;14(8):619-619 [German subjects].

+A39 Ancel PY, Lelong N, Papiernik E, Saurel-Cubizolles MJ, Kaminski M. History

of induced abortion as a risk factor for preterm birth in European countries:results of EUROPOP survey.Human Repro 2004; 19(3): 734-740.

A40 Umeora OUJ, Ande ABA, Onuh SO, Okubor PO et al. Incidence and risk factors

for preterm delivery in a tertiary health institution in Nigeria. J ObstetGynaecol2004;24(8):895-896.

+A41 Moreau C, Kaminski M, Ancel PY, Bouyer J, Escande B, et al. Previous inducedabortions and the risk of very preterm delivery: results of the EPIPAGE study.

British J Obstetrics Gynaecology 2005;112(4):430-437.

A42 Conde-Agudelo A, Belizan JM, Breman R, Brockman SC, Rosas-Bermudez.


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Effect of the interpregnancy interval after an abortion on maternal and perinatalhealth in Latin America.Int J Gynaecol & Obstet2005;89 (Supp. 1):S34-S40.

A43 Stang P, Hammond AO, Bauman P. Induced Abortion Increases the Risk of

Very Preterm Delivery; Results from a Large Perinatal Database.Fertility

Sterility Sept 2005;S159.

A44 Etuk SJ, Etuk IS, Oyo-Ita AE. Factors Influencing the Incidence of Pre-term

Birth in Calabar, Nigeria. Nigerian J Physiological Sciences 2005;20(1-2):63-68.

A45 Poikkens P. Unkila-Kallio L, Vilska S, Repokari L. et al. Impact of InfertilityCharacteristics and treatment modalities on singleton pregnancies after assisted

reproduction. Reprodutive Biomed July 2006;13(1):135-144.

A46 Samin A, Al-Dabbagh, Wafa Y Al-Taee. Pregnancy and Childbirth.BMC2006;6:13.

A47 Smith GCS, Shah I, White IR, Pell JP, Crossley JA, Dobbie R. Maternal and

biochemical predictors of spontaneous preterm birth among nulliparous women: asystematic analysis in relation to degree of prematurity. Intl J Epidem

2006;35(5):1169-1177.

A48 Briunsma F, Lemley J, Tan J, Quinn M. Precancerious changes in the cervix andrisk of subsequent preterm birth. BJOG Jan. 2007;114(1):70-80

A49 Jackson JE, Grobman WA, Haney E, Casele H. Mid-trimester dilation and

evacuation with laminaria does not increase the risk for severe subsequentpregnancy complications. Intl JGynecol Obstet 2007;96:12-15.

*+A50 Brown TS, Adera T, Masho SW. Previous abortion and the risk of low birth

weight and preterm births. J Epidemiol Commun Health 2008;62:16-22

A51 Reime B, Schuecking BA, Wenzlaff P. Reproductive Outcomes in AdolescentsWho Had a Previous Birth or an Induced Abortion Compared to Adolescents'

First Pregnancies. BMC Pregnancy and Childbirth 2008;8:4.


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Brent RooneyByron C. Calhoun, M.D.

ABSTRACT

At least 49 studies have demonstrated a statistically significant

increase in premature births (PB) or low birth weight (LBW) risk in

women with prior induced abortions (IAs). This paper will focus on

the risk of early premature births (EPBs) (< 32 weeks gestation)

and extremely early premature births (XPBs) (< 28 weeks gesta-

tion). Large studies have reported a doubling of EPB risk from two

prior IAs. Women who had four or more IAs experienced, on aver-

age, nine times therisk of XPB, an increase of 800 percent.

These results suggest that women contemplating IA should be

informed of this potential risk to subsequent pregnancies, and that

physicians should be aware of the potential liability and possibleneedfor intensified prenatal care.

Informed consent for an elective surgical procedure must gen-erally cover long-term consequences and not just immediate risk. Awoman considering an induced abortion (IA) should thus expect to

be informed of potential effects on her fertility and the health of fu-ture infants, as well as her own future health. An elevated risk of

bearing a child afflicted with a serious disability such as cerebralpalsy might influence her decision, as well as future liability deter-minations by courts.

Low birth weight (LBW) and premature birth (PB) are the most

important risk factors for infant mortality or later disabilities as

well as for lower cognitive abilities and greater behavioralproblems and thus contribute importantly to the liability exposureof obstetricians.

A literature review retrieved 49 studies that demonstrated atleast 95 percent confidence in an increased risk of preterm birth(PB), or surrogates such as low birth weight or second-trimesterspontaneous abortion, in association with previous induced abor-tions. A list of these studies, which probably does not comprise allsuch studies, is appended to this article. If these 49 statistically sig-nificant associationswere theresult of chancealone, as mayhappenin 5 of 100 tests, IA should be associated with a reduction in PBs,with P


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In 1998, with twice the numberof births(243,679)to analyze as

in 1993, Lumley validated her 1993 results and additionallyshowed that women with four or more prior IAs had an XPB risknine timesthat of primigravidas.

Another large study of 106,345 births in Bavaria, including 85percent of births in the state and 1,146 EPBs, showed a comparabledose-response curve (see Table 2, extracted from Table 2 in the

Bavarian study), confirming the Australian finding of the greatestincreasedrisk for the earliest prematureinfants.In a multivariateanalysisthatincludedmany of thepossiblecon-

founding variables, including previous stillborns, infertility treat-ment, age under 18 or over 35 years, malpresentation, prematurerupture of membranes, and preeclampsia, the effect of even a singleIAremained significant.

A 1999 study of Danish women is especially important be-cause it used an IAregistry, thus eliminating recallbias, thehypoth-esis that women with prior IAswho deliver prematurely aremore ac-curate in reporting reproductive history than women who deliver atfull term, as a possible explanation forthe results.

This study of 61,753 women found an odds ratio for pretermbirth at


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REFERENCES:1

2

3

4

5

6

7

8

9

10

11

12

Escobar GJ, Littenberg B, Petitti DB. Outcome among surviving very lowbirthweightinfants;a meta-analysis. 1991;66:204-211.

BhuttaAT, ClevesMA, CaseyPH, Cradock MM,AnandKJS.Cognitive andbehavioral outcomes of school-aged children who were born preterm: ameta-analysis. 2002;288:728-737.

Park TK, Strauss LT, Hogue CJ, Kim IS. Previous experience of inducedabortion as a risk factorfor fetal death andpreterm delivery.

1984;22:195-202.

Meirik O, Bergstrom R. Outcome of delivery subsequent to vacuum-

aspiration abortion in nulliparous women.1983;62:499-509.

FrankPI, Kay CR,LewisTL, ParishS. Outcome of pregnancyfollowing in-duced abortion. Report from the joint study of the Royal College ofGeneral Practitioners and the Royal College of Obstetricians andGynaecologists. 1985;92:308-316.

Van der Slikke JW, Treffers PE. Influence of induced abortion on gesta-tional duration in subsequent pregnancies. 1978;1(6108):270-272.

Daling JR, Emanuel I. Induced abortionand subsequent outcome of preg-nancyin aseriesofAmericanwomen. 1977;297:1241-1245.

Schott G, Ehrig E, Wulff V. Prospective studies into pregnancies ofprimiparaewith record of therapeutic termination of previouspregnanciesor of spontaneous abortion and assessment of fertility.1980;102:932-938, 939-944

Kalish RB, Chasen ST, Rosenzweig LB, Rashbaum WK, Chervenak FA.

Impactof midtrimester dilation and evacuationon subsequent pregnancyoutcome. 2002;187:882-885.

LaoTT, Ho LF. Induced abortion is nota cause of subsequent preterm de-liveryinteenagepregnancies 1998;13:758-761.

Hogue CJ. Impact of abortion on subsequent fecundity.1986;13:95-103.

Lumley J. The epidemiology of preterm birth.1993;7(3):477-498.

ArchDis Child

JAMA

IntJ GynaecolObstet

Acta Obstet Gynecol Scand

Br J ObstetGynaecol

BMJ

NEnglJMed

Zentralbl Gynaekol

AmJ ObstetGynecol

. HumReprod

Clin ObstetGynaecol

Bailliere's Clin ObstetGynecol

[German].

APPENDIX: Studies that showed a statistically

significant increase in preterm birthafter induced

abortion

*Ancel P-V, Saurel-Cubizolles M-J, Renzo GCD,Papiernik E, Breart G. Very and moderate

preterm births: are the risk factors different?

1999;106:1162-1170.

Barsy G, Sarkany J. Impact of induced abortion

on the birth rate and infant mortality.

1963;6:427-467.

Berkowitz GS. An epidemiologic study of

p r et e rm d e li v er y.

1981;113:81-92.

Bognar Z, Czeizel A. Mortalityand morbidityasso-

ciated with legal abortions in Hungary, 1960-

1973. 1976;66:568-575.

Czeizel A, BognarZ, Tusnady G, etal. Changes in

mean birth weight and proportion of low-

weight births in Hungary

1970;24:146-153.

Drac P, Nekvasilova Z . Premature termination of

pregnancy after previous interruption of preg-

nancy. 1970;35:332-333.

Furusawa Y, Koya Y. The influence of artificial

abortion on delivery. In: Koya Y, ed.

Tokyo: Family

Planning Federation of Japan; 1966:74-83.

Br

J Obstet Gynaecol

Demografia

A m J E p id e mi o l

AmJ PublicHealth

. Br J Prev Soc Med

CeskGynekol

Harmful

Effects of Induced Abortion.

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14

15

16

17

18

19

20

21

22

23

24

25

Hogue CJ, Cates W Jr., Tietze C. Impact of vacuum aspiration on futurechildbearing: a r eview. 1983;15:119-126.

Lumley J. The association between prior spontaneous abortion, prior in-duced abortion and preterm birth in first singleton births.

1998;3:21-24.

Martius JA, Steck T, Oehler MK, Wulf K-H. Risk factors associated withpreterm (


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49Journal of American Physicians and Surgeons Volume 8 Number 2 Summer 2003

Lumley J. Very low birth-weight (less than 1500g)

and previous induced abortion: Victoria 1982-

1983 1986;26:268-272.

Lumley J. The epidemiology of preterm birth.

1993;7(3):477-498.

Lumley J. The association between prior sponta-

neous abortion, prior induced abortion and

preterm birth in first singleton births.

1998;3:21-24.

Martius JA,SteckT, Oehler MK,WulfK-H. Risk fac-tors associated with preterm (


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induced abortion and subsequent preterm birth evidence of risk association

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