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Reproductive outcomes in adolescents who had a previous birth or an induced abortion compared to adolescents'… Reime, Birgit; Schücking, Beate A; Wenzlaff, Paul Jan 31, 2008

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ralssBioMed CentBMC Pregnancy and ChildbirthOpen AcceResearch articleReproductive outcomes in adolescents who had a previous birth or an induced abortion compared to adolescents' first pregnanciesBirgit Reime*1, Beate A Schücking†2 and Paul Wenzlaff†3Address: 1Faculty of Nursing and Healthcare, University of Applied Sciences of the Saarland, Goebenstr. 40, 66117 Saarbrücken, Germany, 2Fachbereich Gesundheitswissenschaften, University of Osnabrück, Albrechtstr 28, 49046 Osnabrück, Germany and 3Centre for Quality Management, Physicians' Chamber of Lower Saxony, Berliner Allee 20, 30175 Hanover, GermanyEmail: Birgit Reime* - breime@nursing.ubc.ca; Beate A Schücking - bschueck@uos.de; Paul Wenzlaff - paul.wenzlaff@zq-aekn.de* Corresponding author    †Equal contributorsAbstractBackground: Recently, attention has been focused on subsequent pregnancies among teenagemothers. Previous studies that compared the reproductive outcomes of teenage nulliparae andmultiparae often did not consider the adolescents' reproductive histories. Thus, the authorscompared the risks for adverse reproductive outcomes of adolescent nulliparae to teenagers whoeither have had an induced abortion or a previous birth.Methods: In this retrospective cohort study we used perinatal data prospectively collected byobstetricians and midwives from 1990–1999 (participation rate 87–98% of all hospitals) in LowerSaxony, Germany. From the 9742 eligible births among adolescents, women with multiple births,>1 previous pregnancies, or a previous spontaneous miscarriage were deleted and 8857 women<19 years remained. Of these 8857 women, 7845 were nulliparous, 801 had one previous birth,and 211 had one previous induced abortion. The outcomes were stillbirths, neonatal mortality,perinatal mortality, preterm births, and very low birthweight. Bivariate and multivariable logisticregression models were conducted.Results: In bivariate logistic regression analyses, compared to nulliparous teenagers, adolescentswith a previous birth had higher risks for perinatal [OR = 2.08, CI = 1.11,3.89] and neonatal [OR= 4.31, CI = 1.77,10.52] mortality and adolescents with a previous abortion had higher risks forstillbirths [OR = 3.31, CI = 1.01,10.88] and preterm births [OR = 2.21, CI = 1.07,4.58]. Afteradjusting for maternal nationality, partner status, smoking, prenatal care and pre-pregnancy BMI,adolescents with a previous birth were at higher risk for perinatal [OR = 2.35, CI = 1.14,4.86] andneonatal mortality [OR = 4.70, CI = 1.60,13.81] and adolescents with a previous abortion had ahigher risk for very low birthweight infants [OR = 2.74, CI = 1.06,7.09] than nulliparous teenagers.Conclusion: The results suggest that teenagers who give birth twice as adolescents have worseoutcomes in their second pregnancy compared to those teenagers who are giving birth for the firsttime. The prevention of the second pregnancy during adolescence is an important public healthobjective and should be addressed by health care providers who attend the first birth or theabortion and the follow-up care. Also, health care workers should attempt to improve thepregnancy outcomes of subsequent teenage pregnancies by addressing modifiable risk factors, forPublished: 31 January 2008BMC Pregnancy and Childbirth 2008, 8:4 doi:10.1186/1471-2393-8-4Received: 17 September 2007Accepted: 31 January 2008This article is available from: http://www.biomedcentral.com/1471-2393/8/4© 2008 Reime et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Page 1 of 7(page number not for citation purposes)example, supporting smoking cessation and utilization of prenatal care.BMC Pregnancy and Childbirth 2008, 8:4 http://www.biomedcentral.com/1471-2393/8/4BackgroundTeenage pregnancy is a significant public health issue.Giving birth during adolescence is strongly associatedwith adverse living conditions in later life [1]. Approxi-mately 1.25 million teenagers become pregnant each yearin the 28 OECD (Organisation for Economic Co-opera-tion and Development) nations [2]. Of those, about halfa million pregnancies will be terminated and approxi-mately three quarters of a million teenagers will becomemothers. In 2003, The Netherlands, Sweden, Denmark,Finland and Slovenia had the lowest adolescent birth ratesin Europe (6/1,000) while the United Kingdom (27/1,000) was characterized by the highest rates [3].In Germany, the proportion of mothers between 10 and18 years of age rose from 0.9% in 2000 to 1.0% in 2006(19/1,000 women of the same age) [4]. Among womenwho had an induced abortion the proportion of adoles-cent women rose from 4.7% in 2000 to 5.5% in 2006 (17/1,000 to 19/1,000). In the western federal state Lower Sax-ony between 2000 and 2006 the rate of live births rangedfrom 22 to 18 while the rates in Berlin and in the easternfederal states were 20–70% higher during this period oftime. The same regional pattern can be observed regardingthe rates of induced abortions [4].Recently, attention has been focused on subsequent preg-nancies among teenage mothers. The likelihood of a sec-ond birth among adolescent mothers is much greater thanthe likelihood of a first birth among teen females whohave not had a child yet. For example, in the United Statesin 2001, there were 35.7 births per 1000 females aged 15to 19 years who never had a birth compared to 175.1births per 1000 females aged 15 to 19 years who previ-ously had one birth [5]. Accordingly, twenty percent ofteen births occurred to young women who had beenmothers already. In a representative sample of adolescentmothers in the US about two thirds reported that the sec-ond pregnancy was not intended [6]. In Germany, amongthose teenagers who had an abortion in 2006, 2.8%reported to have a child already [4].A small number of studies have examined the relationshipbetween parity and reproductive outcomes among teenag-ers. Cross-sectional studies suggest a lower risk for lowbirthweight [7] and for neonatal, postneonatal and infantmortality [7-9] in the first pregnancy of adolescentwomen. However, the results of longitudinal studies aresimilar to studies on adult women populations [10], andindicate that higher rates of low birthweight infants [11]and intrauterine growth retardation [12] are associatedwith teenagers' first birth compared to their second.tional studies based on the linking of birth and deathrecords could not access relevant confounders [7,9]. Lon-gitudinal studies that followed individuals over time hadsamples that didn't reflect the general population, werebased on small geographical areas and/or lacked statisticalpower because of a small sample size [12-15]. Only onelongitudinal study considered the adolescents' obstetrichistory regarding abortions and miscarriages [13]. Theobjective of this study was to compare the perinatal out-comes (rates of stillbirths, neonatal and perinatal mortal-ity, preterm birth and very low birthweight) ofnulliparous teenagers and teenagers who previously hadan induced abortion or a live- or stillbirth after adjust-ment for potential confounders (maternal nationality,partner status, smoking, prenatal care and pre-pregnancyBMI).MethodsStudy design and settingWe examined the relationship between reproductive his-tory and reproductive outcomes among nulliparous ado-lescents and adolescents who had a previous abortion ora previous birth using routinely collected perinatal data.In most federal states of Germany, pregnancy and deliv-ery-related data are maintained in a central perinatal reg-istry. Our study is based on the Perinatal Surveys of theyears 1990–1999 in Lower Saxony (742,031 cases). Pro-spectively during pregnancy, midwives and obstetricianscollect data on maternal socio-demographic background,maternal health and behaviour, obstetrical care and inter-ventions during pregnancy in a "mother's passport". Themother receives this document at the first prenatal visitduring her first pregnancy and the data on all of her preg-nancies are recorded in this passport. This refers toinduced abortions, and miscarriages or stillbirths as wellas to live-births. The mother has to bring this passportwith her when she gives birth in hospital to inform thestaff on her reproductive history. Information on inter-ventions during birth and infant outcomes up to sevendays post partum are collected after birth. Hospital staffelectronically submit registry data derived from themother's passports and delivery records to the Centre forQuality Management of the Physicians' Chamber ofLower Saxony. Because these data are collected routinelyon an anonymous basis (comparable to vital statistics) inGermany informed consent is not required for this proce-dure. All live-births and stillborn infants with a birth-weight of >499 grams (until April 1st 1994: >999 grams)are included in the registry. The data are restricted to hos-pital births that make up more than 98 percent of allbirths in Lower Saxony. The participation rate of the hos-pitals in Lower Saxony was 87 percent in 1990, and stead-ily increased to 98 percent in 1999. The non-participatingPage 2 of 7(page number not for citation purposes)Previous studies on parity and reproductive outcomes inadolescents had several important limitations. Cross-sec-hospitals stated to have insufficient resources for partici-pation. However, they did not differ from the participat-BMC Pregnancy and Childbirth 2008, 8:4 http://www.biomedcentral.com/1471-2393/8/4ing hospitals in terms of health outcomes, the type ofhospital, number of births per year, or any other knowncharacteristic [16].Lower Saxony is a large federal state in the northwest ofGermany (Hanover is the capital) that consists of severallarge cities as well as vast rural areas. The population inLower Saxony is rather homogeneous in terms of ethnic-ity. During the 1990's, the proportion of female migrantadolescents between 15 and 20 years of age ranged from6.3 percent to 8.1 percent [17].Study sampleIn this sample there are 7845 nulliparous teenagers, 801teenagers with one previous live- or stillbirth, and 211teenagers who had one previous abortion. We restrictedour sample to these groups because we attempted to avoideffects resulting from unmeasured confounders that areassociated with higher order births and heterogeneousreproductive histories. Because we used anonymised datafrom a perinatal registry, ethic approval was not required.VariablesReproductive historyAdolescents with no prior pregnancies recorded in themother's passport were defined as nulliparous. Teenagerswith a previous pregnancy were divided into women witha previous live- or stillbirth and those with a history ofabortion.Outcomes: Definitions and denominatorsIn Germany, neonatal mortality is defined as the death ofa live born infant (showing heartbeat, lung breathing,and/or pulsation of the cord) of any weight occurring upto 7 days post partum. Stillbirth is defined as a birth of aninfant without live-signs weighing more than 999 grams(until March 31st 1994) or more than 499 grams (fromApril 1st 1994 onward). Perinatal mortality is defined asthe sum of stillbirths and neonatal mortality and wasobtained by summing the number of infants coded asstillbirths and as neonatal deaths. For all three variablesthe denominator was all births. Preterm birth is defined asbirths occurring before 259 days (37+0 weeks) of gesta-tion, very low birthweight (VLBW) is defined as infantsweighing <1500 grams. The denominator of the last twooutcomes was all live births.Potential ConfoundersNationality was coded as German national or migrant,and partner status was coded as living single or with apartner. The variable smoking during pregnancy was col-lapsed into binary format (0 versus any cigarettes). Inade-quate prenatal care (yes/no) was determined by thetiation of prenatal care and the total number of prenatalvisits, adjusted for gestational age at birth. Less than 50percent of the recommended number of prenatal visits fora given gestational age and initiation of prenatal care afterthe first trimester is defined as "inadequate care" [18].BMI was calculated as pre-pregnancy body weight (in kil-ograms) divided by the square of height (in meters) andwas entered as a continuous variable.Statistical analysesUsing SPSS 12.0, we performed chi-square- and t-tests tostudy the relationship between reproductive history andthe potential confounders. Crude odds ratios, including95 percent-confidence intervals, were computed to exam-ine the associations between the adolescents' reproductivehistory (referent group: nulliparous teenagers) and thepregnancy outcomes. In multivariable logistic regressionmodels, these associations were adjusted for nationality,partner status, smoking, prenatal care, and BMI. Diagnos-tic analyses were performed on the logistic models as rec-ommended by Hosmer and Lemeshow (1989) [19]. Wedefined p < 0.05 as statistically significant. In this retro-spective cohort study there were missings related to expo-sures collected during prenatal visits and related tooutcomes collected after birth. Cases with missing valueswere deleted.ResultsParticipantsThere were 9742 births among teenagers aged 13–18years. After exclusion of multiple births (n = 130), ≥ 2 pre-vious pregnancies (n = 237) and a previous spontaneousmiscarriage (as a proxy for a potential genetic disorder) (n= 377), 8857 young women remained. Of these 8857women, 7845 were nulliparous, 801 were teenagers withone previous live- or stillbirth, and 211 had one previousabortion.Demographic characteristicsThe majority (96.1 percent) of the adolescents were agedbetween 16 and 18 years and more than one third (37.2percent) were migrants. Among migrants, the majoritywere from the Middle East (51.2 percent), Mediterraneancountries (23.2 percent) and Eastern Europe (17.4 per-cent).Table 1 contains the results of the analyses of the relation-ship between reproductive history and potential con-founders. Among teenagers who had a previous abortion,the proportion of smokers (46.0 percent) and single par-ents (40.1 percent) was higher than among the two othergroups (p < 0.001). About two thirds of adolescents witha previous birth compared to 13.7 percent of women whoPage 3 of 7(page number not for citation purposes)Adequacy of Prenatal Care Utilisation (APNCU) Index[18], which combines information about the time of ini-previously had an abortion and 34.8 percent of nullipa-rous women were of migrant nationality (p < 0.001).BMC Pregnancy and Childbirth 2008, 8:4 http://www.biomedcentral.com/1471-2393/8/4Inadequate prenatal care was observed mostly amongadolescents with a previous birth (42.6 percent), followedby nulliparous adolescents (32.4 percent) and adolescentswith a history of abortion (29.4 percent, p < 0.001).Crude analysesCompared to nulliparous adolescents, adolescents with aprevious birth were at higher risk for perinatal [OR = 2.08,CI 1.11, 3.89] and neonatal mortality [OR = 4.31, CI 1.77,10.52]. Teenagers who previously had an abortion had a3.3-fold [95 percent CI = 1.01, 10.88] higher risk for astillbirth and a 2.2-fold [95 percent CI = 1.07, 4.58] higherrisk for a preterm born infant than nulliparous adoles-cents (Table 2).Multivariable analysesThe confounders we included in the analyses were signif-icantly related to all of the outcomes (stillbirths, neonatalmortality, perinatal mortality, preterm births, and verylow birthweight) (data not shown) and to the reproduc-tive history among teenagers (Table 1). In the logisticregression model adjusted for all confounders, infants ofadolescents with a previous birth were at higher risk forperinatal mortality [OR = 2.35, CI 1.14, 4.86] and neona-tal mortality [OR = 4.70, CI 1.60, 13.81]. Adolescents withTable 1: Maternal characteristics among teenagers with different reproductive histories (chi-square tests and t-tests).Nulliparous Previous birth History of abortion P-valueNationality <0.001Migrant n (%) 2730 (34.8) 535 (66.8) 29 (13.7)German n (%) 5115 (65.2) 266 (33.2) 182 (86.3)Partner status <0.001Single parent n (%) 2562 (34.0) 112 (14.2) 81 (40.1)Cohabiting n (%) 4980 (66.0) 678 (85.8) 121 (59.9)Smoking <0.001Yes n (%) 2275 (30.2) 187 (24.1) 93 (46.0)No n (%) 5256 (69.8) 589 (75.9) 109 (54.0)Prenatal care <0.001Inadequate n (%) 2541 (32.4) 341 (42.6) 62 (29.4)Adequate n (%) 5304 (67.6) 460 (57.4) 149 (70.6)BMI Mean (SD) 22.8 (3.6) 23.5 (4.0) 23.0 (3.6) <0.001Table 2: Results from bivariate and multivariable regression models regarding the associations between reproductive history and outcomes.n (%) Crude OR (95%-CI) AOR* (95%-CI)Perinatal mortalityNulliparous 57 (0.7) 1.0 1.0Previous birth 12 (1.5) 2.08 [1.11, 3.89] 2.35 [1.14, 4.86]History of abortion 4 (1.9) 2.64 [0.95, 7.35] 1.83 [0.43, 7.68]Neonatal mortalityNulliparous 16 (0.2) 1.0 1.0Previous birth 7 (0.9) 4.31 [1.77, 10.5] 4.70 [1.60, 13.8]History of abortion 1 (0.5) 2.33 [0.31, 17.7] 4.64 [0.58, 37.5]StillbirthNulliparous 36 (0.5) 1.0 1.0Previous birth 5 (0.6) 1.15 [0.41, 3.26] 1.09 [0.32, 3.71]History of abortion 3 (1.5) 3.31 [1.01, 10.9] 1.23 [0.17, 9.15]Very low birthweightNulliparous 110 (1.4) 1.0 1.0Previous birth 8 (1.0) 0.62 [0.27, 1.43] 0.53 [0.21, 1.34]History of abortion 6 (2.8) 2.02 [0.81, 5.02] 2.74 [1.06, 7.09]Preterm birthNulliparous 275 (3.5) 1.0 1.0Previous birth 32 (4.0) 1.13 [0.66, 1.88] 1.08 [0.58, 2.02]History of abortion 17 (7.7) 2.21 [1.07, 4.58] 1.90 [0.77, 4.69]Page 4 of 7(page number not for citation purposes)Acknowledgment: Crude OR = crude odds ratios, AOR = adjusted odds ratios, 95%-CI = 95% confidence intervals.*Adjusted for nationality, partner status, smoking, inadequate prenatal care and BMI.BMC Pregnancy and Childbirth 2008, 8:4 http://www.biomedcentral.com/1471-2393/8/4a previous induced abortion had a higher risk for very lowbirthweight infants [OR = 2.74, CI 1.06, 7.09]. There wereno significant differences in terms of preterm births andstillbirths related to obstetric history.DiscussionUsing routinely collected perinatal data we examined therelationships between obstetric history and reproductiveoutcomes among adolescents. Compared to nulliparae,adolescents with a previous birth had a more than twofoldhigher risk for perinatal mortality and a more than four-fold higher risk for neonatal mortality.The results of this study confirm the findings of studieswith cross-sectional designs. For example, Hellerstedt etal. [8] found that the crude risk for neonatal deaths was 20percent higher among multiparae compared to primipa-rous teenagers. Additionally, in the US, the risk for neona-tal mortality was about 1.5-fold increased among 18–19year old multiparae compared to primiparae of the sameage [7]. Our study contradicts findings from a longitudi-nal US-study that found an almost twofold higher risk forperinatal deaths and a threefold higher risk for stillbirthsamong nulliparous women compared to adolescents witha previous birth [13]. However, the study was underpow-ered because of a small sample size and the results werenot statistically significant. Other longitudinal studiesalso had limited sample sizes and could not examine rareoutcomes such as perinatal mortality [11,12,14].Due to the lack of studies on adolescent multiparae thatconsidered confounders, the selection of potential con-founders in this study derived from research on adoles-cent primiparae or adult women [18,20,21]. Theconfounders we examined did not explain the elevatedrisks for perinatal and neonatal mortality among adoles-cents with a previous birth compared to nulliparous teen-agers. Rather, the adjustment for confoundersstrengthened the observed relationships. To inform futurepreventive efforts, further studies should attempt to iden-tify the mediating factors that increase the risk amongadolescents with a previous birth for neonatal and perina-tal mortality.Previous studies on the risks associated with a history ofabortion among teenagers are sparse. Lao and Ho [22]found that a previous induced abortion among HongKong teenagers was not related to a higher risk for pretermbirth. In our study, teenagers with a history of an abortionhad a 3.4-fold higher risk for a stillbirth and a 2.2-foldhigher risk for a preterm born infant than nulliparousadolescents. After adjustment for confounders these asso-ciations disappeared. In our study and in Hong Kong [22]with no abortion history. In the same group of teenagers,compared to nulliparous women, the risk for a very lowbirthweight infant was increased in the adjusted model.Because the confounders we examined (such as smokingduring pregnancy or inadequate prenatal care) are relatedto both stillbirths [23] and very low birthweight [24] fur-ther studies are needed to understand this contradictoryresult.In our sample, the rates of adverse outcomes largely corre-spond with Scottish data [10] but they were lower com-pared to the American studies of Blankson et al. (1993)[12] and Hellerstedt et al. (1995) [8], especially regardingpreterm birth. However, neither the ethnic compositionnor the social context of these US studies and our studycan readily be compared. One reason for the lower inci-dence rates in preterm birth in Lower Saxony may besought in the fact that the perinatal registry does not cover(planned and unplanned) out-of-hospital births. Also, theincidence rate of adolescents' pregnancies in Lower Sax-ony is slightly below the German average. This may reflecta less adverse environment compared to those areas withhigher incidence rates such as Berlin and the eastern fed-eral states, areas with higher unemployment rate, in par-ticular among adolescents.We have no information on known risk factors for adverseoutcomes, especially of teenage pregnancies, such asdomestic violence, stress, or poverty [20,25]. Smith andPell compared the birth outcomes of primiparae andsecundiparae between adolescent and adult mothers andfound no differences among primiparae but higher peri-natal mortality among adolescent than among adultsecundiparae [10]. Smith and Pell concluded that a sec-ond birth during adolescence probably occurs more oftenin the context of poverty and poor nutrition than a secondbirth among mature women. Therefore, among teenagersliving in a disadvantaged social context the accumulativeburden of a second pregnancy may result in adverse out-comes. Our sample, however, is characterized by a vastproportion of migrant adolescents who usually are mar-ried and have access to strong support networks withintheir communities. The differences regarding the socialcontext and behavioural characteristics (such as migrantstatus, lone motherhood, and smoking) among the threereproductive groups in our sample may point at the neces-sity for sociodemographically tailored approaches whenattempting to improve the reproductive health of thesewomen.According to Klerman, findings from previous cross-sec-tional studies may be biased because they often comparedany higher order births to nulliparous teenagers andPage 5 of 7(page number not for citation purposes)teenagers with a previous abortion were characterized bya much higher smoking rate than the adolescent mothersmissed important confounders [26]. The results of ourstudy cannot readily be compared to these studies becauseBMC Pregnancy and Childbirth 2008, 8:4 http://www.biomedcentral.com/1471-2393/8/4we deleted adolescents who previously had a spontaneousmiscarriage from the sample and thus only examined"true" nulliparae. Contrary to Hellerstedt et al. we com-pared the outcomes of the first birth to the outcomes ofthe second pregnancy while higher order pregnancieswere excluded [8]. Additionally, we considered the out-come very low birthweight (< 1500 grams) instead of lowbirthweight (< 2500 grams) because the predictive valueof the latter variable for children's health is still beingdebated [27]. We did not use intrauterine growth retarda-tion as an outcome because the underlying growth normsrefer to the German population and may not be valid formigrant newborns who account for more than one thirdin our sample. Previous studies on subsequent teenagepregnancy mostly have been from the US. However, theGerman adolescent population differs from the US popu-lation on several important aspects such as the ethniccomposition. Also, contrary to the US, in Germany, prena-tal care is free for all women regardless of their age, migra-tion or employment status. Health insurance ismandatory. For refugees and for unemployed women thecosts of prenatal care are covered by the community. Con-sistent with other studies from countries with free provi-sion of prenatal care a huge proportion of teenagers ineach reproductive group chose not to utilize this offer[28]. These adolescents may be characterized by a lowerlevel of knowledge about the availability of prenatal care.Those who have had a previous birth or an abortion mayanticipate negative comments on their condition byhealth care providers [28].Our study has several limitations. To suggest causality thistype of study has to be longitudinal. Adolescents whohave a birth following a prior birth or an abortion are dif-ferent in many ways from those who have a first birth withno previous pregnancies [26]. We have controlled fornationality, partner status, smoking, pre-pregnancy BMIand adequacy of prenatal care to differentiate betweenadolescents with different reproductive histories. How-ever, we have no information on birth spacing. It may wellbe that a short inter-pregnancy interval is one of theunderlying causes of worse outcomes among adolescentswho had a previous pregnancy [29]. Intimate partner vio-lence is another known risk factor for subsequent preg-nancies during adolescence that we were not able toexamine [30]. Alcohol is a known teratogenic substancethat operates under a dose-response mechanism and druguse is associated with adverse pregnancy outcomes as well[31,32]. We could not access information on these sub-stances. Further known risk factors for adverse pregnancyoutcomes such as an unwanted pregnancy, stress, poverty,and vaginal infections also are not assessed in the routineperinatal survey. In summary, it is possible that our find-Although the rate of non-participating hospitals is rathersmall (2–13 percent), we cannot rule out a selection bias.Small numbers in some cells resulted in broad confidenceintervals.Induced abortions usually are recorded in the mother'spassport but in the next pregnancy the women can chooseto visit a new gynaecologist or midwife without bringingher mother's passport and thus deny the previous preg-nancy. Therefore, underreporting of previous abortions ispossible may have resulted in a classification bias.A high proportion of teenagers who already gave birth toa child were characterized by Non-German nationality.Although we adjusted for nationality we cannot disregardthat residual confounding may have occurred and thatcharacteristics associated with migrant status might haveaffected the risk for adverse outcomes.However, the current study expands on previous studiesin several ways: it is not based on vital statistics but ratheron data from a population sample prospectively collectedby physicians and midwives. Thus, external validity andgeneralizability are satisfactory. Additionally, we incorpo-rated several relevant confounders such as smoking in ouranalyses. Our study not only considers the adolescents'parity but draws attention explicitly to the reproductivehistory.ConclusionWe found among adolescents who already had a previouspregnancy a higher risk for the infant than among teenag-ers who reported to be pregnant for the first time even ifrelevant confounders are controlled. Among adolescentswith a history of an abortion, the risks for stillbirth andpreterm birth are increased but this can be explained byconfounders. The prevention of the second pregnancyduring adolescence is an important public health objec-tive and should be addressed by health care providers whoattend the first birth or the abortion and the follow-upcare. Given the high proportion of migrant adolescentmothers in this sample, awareness of the cultural aspectsof reproductive health is an important issue for research-ers and health care workers to consider. Furthermore,health care workers should attempt to improve the preg-nancy outcomes of subsequent teenage pregnancies byaddressing modifiable risk factors, for example, support-ing smoking cessation efforts. Studies that focus on exam-ining the hypothesized mediators of social disadvantage,such as domestic violence, poverty, social support andeducational opportunities, may also facilitate the devel-opment of effective interventions.Page 6 of 7(page number not for citation purposes)ings might be eliminated if we had accessed more con-founders or if the study had a longitudinal design.Publish with BioMed Central   and  every scientist can read your work free of charge"BioMed Central will be the most significant development for disseminating the results of biomedical research in our lifetime."Sir Paul Nurse, Cancer Research UKYour research papers will be:available free of charge to the entire biomedical communitypeer reviewed and published immediately upon acceptancecited in PubMed and archived on PubMed Central BMC Pregnancy and Childbirth 2008, 8:4 http://www.biomedcentral.com/1471-2393/8/4Competing interestsThe author(s) declare that they have no competing inter-ests.Authors' contributionsBR analysed the data and mainly wrote the manuscript. BSassisted with interpreting the results and writing the man-uscript. PW assisted with interpreting the results and writ-ing the manuscript. The manuscript has been read andapproved by all three authors.AcknowledgementsThe study is part of a project funded by a Michael Smith Foundation for Health Research (MSFHR) research unit infrastructure grant that was used to hire the first author in British Columbia, Canada.References1. Bradley T, Cupples ME, Irvine H: A case control study of a depri-vation triangle: Teenage motherhood, poor educationalachievement and unemployment.  Int J Adolesc Med Health 2002,14:117-123.2. UNICEF: 'A league table of teenage births in rich nations',Innocenti Report Card No.3, July 2001.  UNICEF InnocentiResearch Centre, Florence  [http://www.unicef-irc.org/publications/pdf/repcard3e.pdf]. accessed December 12th 20073. European population Committee of the Council of Europe: Recentdemographic developments in Europe 2005.  Bruxelles 2006.4. 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