Previous abortion and the risk of low birth weight and preterm births

OBJECTIVE: To investigate the association between previous abortion and low birth weight (LBW) and preterm birth (PB). METHOD: The study examined live, singleton births using data from the United States Collaborative Perinatal Project. Logistic regression was used to control for obstetric and medical history, and lifestyle and demographic factors. RESULT: Compared with women with no history of abortion, women who had one, two and three or more previous abortions were 2.8 (95% CI 2.48 to 3.07), 4.6 (95% CI 3.94 to 5.46) and 9.5 (95% CI 7.72 to 11.67) times more likely to have LBW, respectively. The risk for PB was also 1.7 (95% CI 1.52 to 1.83), 2.0 (95% CI 1.73 to 2.37) and 3.0 (95% CI 2.47 to 3.70) times higher for women with a history of one, two and three or more previous abortions, respectively. CONCLUSION: Previous abortion is a significant risk factor for LBW and PB, and the risk increases with the increasing number of previous abortions. Practitioners should consider previous abortion as a risk factor for LBW and PB.     

Risk of ectopic pregnancy and previous induced abortion.

OBJECTIVES: This study investigated the role of prior history of induced abortion in subsequent ectopic pregnancies. METHODS: Data from two French case-control studies were used to examine the effect of induced abortion on ectopic pregnancy risk. Case patients (n = 570) were women admitted for ectopic pregnancy during the study period; controls (n = 1385) were women who delivered in the same center. RESULTS: The analysis among women with no previous ectopic pregnancy showed that, after control for the main ectopic pregnancy risk factors, prior induced abortion was associated with an increased risk of ectopic pregnancy (odds ratio [OR] = 1.5, 95% confidence interval [CI] = 1.0, 2.0); there was a significant trend between number of previous induced abortions and ectopic pregnancy risk (ORs = 1.4 for 1 previous induced abortion and 1.9 for 2 or more). CONCLUSIONS: This study suggests that induced abortion may be a risk factor for ectopic pregnancy for women with no previous ectopic pregnancy, particularly in the case of women who have had several induced abortions.     

Physical abuse during pregnancy and risk of low-birthweight infants among aborigines in Taiwan

OBJECTIVES: The aim of this study was to assess whether physical abuse during pregnancy is associated with an increased risk of giving birth to a low-birthweight (LBW) infant. STUDY DESIGN AND METHODS: A cross-sectional survey was conducted and 1143 aboriginal women were recruited into this study. The Abuse Assessment Screen was used to collect information regarding maternal physical abuse, and infants' birth weights were obtained from hospital medical records. Multiple logistic regression was used to estimate the association of LBW with physical abuse during pregnancy, adjusting for behavioural and sociodemographic variables. RESULTS: Of the women experiencing physical abuse during their recent pregnancy, 11.76% delivered a LBW infant, compared with 5.78% of women who did not experience physical abuse [odds ratio (OR) 1.97, 95% confidence intervals (CI) 1.07-3.63]. Physical abuse during pregnancy was also significantly associated with low weight gain in the prenatal period. Univariate analysis revealed that delivery of a LBW infant was associated with maternal alcohol use, maternal betel chewing and maternal educational level. Multiple logistic regression was performed, adjusting for prenatal weight gain, maternal height, maternal years of education, maternal alcohol use and maternal betel quid use. It was found that women who reported physical abuse with injuries during pregnancy had a 2.4-fold higher risk of delivering a LBW infant compared with women who did not report physical abuse with injuries (adjusted OR=2.43, 95%CI 1.06-5.55). CONCLUSIONS: These findings suggest that physical abuse during pregnancy is an independent risk factor for delivery of a LBW infant. Prenatal care for aboriginal women should be coupled with routine systematic screening for the presence of abuse during pregnancy, and adequate support and interventions for abused women.     

中国低出生体重儿危险因素的病例对照研究

目的 探讨我国不同特征低出生体重儿发生的有关危险因素。方法 1998年7－10月,对我国11个省44个县市的999例低出生体重儿进行1：！病例对照研究。结果 我国低体重儿发生的危险因素主要为多胎、孕周不足、孕期异常、孕期营养差、母亲疾病史及母亲程度低等,其OR值分别为106．9、18．79、3．42、1．93、2．61和1．43。各危险因素在沿海、内地及边远地区的分布差异有显著性。农村低体重儿的原因主要为宫内发育迟缓（71．6％）,城市低体得儿的原因还包括多胎和早产。早产及宫内发育不全的低出生体重儿之间的危险因素存在差异。结论 有针对性地开展防治工作是降低我国低体重儿出生率的有效措施。     

Abortion and its effect on risk of preeclampsia and transient hypertension

We examined the effect of abortion type, number, and gestational age on the risk of preeclampsia and transient hypertension among women who received prenatal care from 13 obstetric practices in southern Connecticut between April 1988 and December 1991 (N = 2,739). Subjects were interviewed before 16 weeks' gestation regarding reproductive history and pregnancy-related risk factors. We estimated the risk of preeclampsia (N = 44) and transient hypertension (N = 172) among nulliparous women who had had one or more abortions, with nulliparous women with no abortion as the referent group. Similar effects were seen for one spontaneous or induced abortion, when analyzed separately. A single prior abortion was associated with a decreased risk of preeclampsia [odds ratio (OR) = 0.35; 95% exact confidence interval (CI) = 0.09-1.01]. One abortion had only a small association with risk of transient hypertension (OR = 1.09, 95% exact CI = 0.68-1.72); however, a history of two or more abortions was associated with a decreased risk (OR = 0.42, 95% exact CI = 0.16-0.94). Among nulliparous women with a history of one abortion, a decreased risk of both hypertensive disorders was observed among women whose aborted pregnancy ended at > or =3 months gestation. These findings suggest that a history of abortion in nulliparous women is a protective factor against the risk of preeclampsia in the subsequent pregnancy.     

Is Maternal Smoking during Early Pregnancy a Risk Factor for All Low Birth Weight Infants?

Background

Low birth weight (LBW) infants do not form a homogeneous group; LBW can be caused by prematurity or poor fetal growth manifesting as small for gestational age (SGA) infants or intrauterine growth retardation. We aimed to clarify the relationship of maternal smoking with both SGA and preterm LBW infants.

Methods

The study population comprised pregnant women who registered at the Koshu City between January 1, 1995, and December 31, 2000, and their children. We performed multivariate analyses using multiple logistic regression models to clarify the relationship of maternal smoking during pregnancy with the SGA outcome and preterm birth in LBW infants.

Results

In this study period, 1,329 pregnant women responded to questionnaires, and infant data were collected from 1,100 mothers (follow-up rate: 82.8%). The number of LBW infants was 81 (7.4%). In this cohort, maternal smoking during early pregnancy was associated with LBW and the SGA outcome. Maternal smoking during early pregnancy was a risk factor for LBW with SGA outcome and for LBW with full-term birth. However, it was not a risk factor for LBW with appropriate weight for gestational age (AGA) and LBW with preterm birth.

Conclusion

These results suggested that LBW with AGA and LBW with preterm birth were associated with other risk factors that were not considered in this study, such as periodontal disease. For the prevention of LBW, not only abstinence from smoking during pregnancy but also other methods such as establishing a clinical setting should be adopted.Key words: Infant, Low Birth Weight; Pregnancy; Risk Factors; Smoking     

Recurrence of low birth weight in siblings

The recurrence of low birth weight (LBW, < 2500 g) in full siblings was studied in 3286 singleton infants born between 1966 and 1986 to 1677 male U.S. Army veterans who were part of a nationwide health study. Hospital of birth medical records were abstracted for these children. Mean birth weights, risks of LBW, LBW occurring with preterm delivery (< 37 weeks) (LBW/p), and LBW in term infants (LBW/t) were examined in successive singleton siblings according to LBW status of prior siblings. The risk of LBW in infants who had prior siblings with LBW was 9.9%, compared with a risk of 2.8% in infants who had prior siblings without LBW (OR = 3.8, 95% CI 2.0–7.3). The excess recurrence of LBW was specifically due to LBW/p. Infants with prior siblings with LBW/p were at high tisk of LBW/p (OR = 9.2, CI 4.4–19.6) but not of LBW/t (OR = 2.0, CI 0.1–9.1). Using modified logistic regression techniques that incorporate familial risks and the effects of other risk factors, the excess sibling recurrence risk of LBW and LBW/p could not be explained by the tendency for recurrence in siblings of other risk factors for LBW, such as pregnancy complications, maternal illnesses, and birth defects. Although the familial factors involved in LBW may or may not be genetic in nature, such factors need to be investigated in epidemiologic studies of LBW and prematurity.     

Induced abortion and low birthweight in the following pregnancy

BACKGROUND: To examine whether induced abortion increases the risk of low birthweight in subsequent singleton live births. METHODS: Cohort study using the Danish Medical Birth Registry (MBR), the Hospital Discharge Registry (HDR), and the Induced Abortion Registry (IAR). All women who had their first pregnancy during 1980-1982 were identified in the MBR, the HDR, and the IAR. We included all 15,727 women whose pregnancy was terminated by a first trimester induced abortion in the induced abortion cohort and 46,026 women whose pregnancy was not terminated by an induced abortion were selected for the control cohort. All subsequent pregnancies until 1994 were identified by register record linkage. RESULTS: Low birthweight (<2500 g) in singleton term live births occurred more frequently in women with one, two, three or more previous induced abortions, compared with women without any previous induced abortion of similar gravidity, 2.2% versus 1.5%, 2.4% versus 1.7%, and 1.8% versus 1.6%, respectively. Adjusting for maternal age and residence at time of pregnancy, interpregnancy interval, gender of newborn, number of previous spontaneous abortions and number of previous low birthweight infants (control cohort only), the odds ratios (OR) of low birthweight in singleton term live births in women with one, two or more previous first trimester induced abortions were 1.9 (95% CI: 1.6, 2.3), and 1.9 (95% CI: 1.3, 2.7), respectively, compared with the control cohort of similar gravidity. High risks were mainly seen in women with an interpregnancy interval of more than 6 months. CONCLUSIONS: The findings suggest a positive association between one or more first trimester induced abortions and the risk of low birthweight in subsequent singleton term live births when the interpregnancy interval is longer than 6 months. This result was unexpected and confounding cannot be ruled out.     

Social differences of very preterm birth in Europe: interaction with obstetric history. Europop Group.

Social differences of very preterm birth (22-32 completed weeks of amenorrhea) were studied using data from a large case-control survey in Europe between 1994 and 1997; 1,675 very preterm births and 7,965 full-term births were included. The relation between social factors and very preterm birth was studied according to obstetric history and the mode of delivery onset. Very preterm birth was significantly related to low educational level among women with no previous adverse pregnancy outcome (odds ratio (OR) = 2.67, 95 percent confidence interval (CI) 1.66-4.28) and among primigravid women and those with previous first-trimester abortion (OR = 2.01, 95 percent CI 1.56-2.58). In this group, unemployment of all household members was associated with a double risk of very preterm birth. No significant association between very preterm birth and socioeconomic status was observed among women with previous second-trimester abortion or preterm birth. Socioeconomic indicators remained significantly associated with both spontaneous and induced very preterm births among women with no previous late fetal loss or preterm birth. The results are consistent with social factors affecting the risk of very preterm birth, but the relation differs according to obstetric history.     

昆山市2001～2009年低出生体重儿流行病学分析

目的:描述昆山市2001～2009年9年间低出生体重(LBW)发生率,分析产妇及胎儿特征对低出生体重的影响。方法:利用昆山市《围产保健监测系统》研究33 631对产妇与胎儿,使用单因素与多因素无序多分类Logistic回归分析来估计各因素对出生体重的影响。结果:LBW发生率为1.86%。产妇超重肥胖、有人工流产史、男性胎儿可减小LBW发生风险。产妇体质指数偏低、初产妇、习惯性流产史可增加LBW发生风险。按照体质指数(BMI)分层,相对于LBW,BMI偏低组,高水平的孕期体重变化均可减小LBW胎儿发生风险。BMI正常组,高水平的孕期体重变化可减小LBW胎儿发生风险。没有发现在超重与肥胖组产妇孕期体重变化与分娩LBW胎儿之间存在统计学关联。结论:LBW发生率为1.86%,产妇与胎儿特征综合影响LBW。体重偏低与正常人群中,高水平的孕期体重变化可减小LBW发生风险。     

Predictors of vaginal bleeding during the first two trimesters of pregnancy

This study evaluates maternal age, race, cigarette smoking, prior spontaneous abortion, prior induced abortion, and prior preterm birth in relation to vaginal bleeding during the first two trimesters of pregnancy. Information on vaginal bleeding and predictors came from the Pregnancy, Infection, and Nutrition Study, which enrolled 2806 pregnant women at 24-29 weeks' gestation during 1995-2000 in central North Carolina, USA. Generalised estimating equations were applied to take into account repeated episodes of vaginal bleeding during pregnancy. Women with advanced maternal age and passive smoking exposure were more likely to experience more intense vaginal bleeding during pregnancy, as were women with prior preterm birth. More intense bleeding was also more likely to be reported among women with multiple prior spontaneous abortions or multiple prior induced abortions, but not among women with a single prior spontaneous or induced abortion. The combination of prior spontaneous and induced abortion showed a dose-response association with the occurrence of vaginal bleeding during pregnancy.     

Modelling prior reproductive history to improve prediction of risk for very preterm birth

Watson LF, Rayner J‐A, King J, Jolley D, Forster D, Lumley J. Modelling prior reproductive history to improve prediction of risk for very preterm birth. Paediatric and Perinatal Epidemiology 2010. In published studies of preterm birth, analyses have usually been centred on individual reproductive events and do not account for the joint distributions of these events. In particular, spontaneous and induced abortions have often been studied separately and have been variously reported as having no increased risk, increased risk or different risks for subsequent preterm birth. In order to address this inconsistency, we categorised women into mutually exclusive groups according to their reproductive history, and explored the range of risks associated with different reproductive histories and assessed similarities of risks between different pregnancy histories. The data were from a population‐based case–control study, conducted in Victoria, Australia. The study recruited women giving birth between April 2002 and April 2004 from 73 maternity hospitals. Detailed reproductive histories were collected by interview a few weeks after the birth. The cases were 603 women who had had a singleton birth between 20 and less than 32 weeks gestation (very preterm births including terminations of pregnancy) and the controls were 796 randomly selected women from the population who had had a singleton birth of at least 37 completed weeks gestation. All birth outcomes were included. Unconditional logistic regression was used to assess the association of very preterm birth with type and number of prior abortions, prior preterm births and sociodemographic factors. Using the complex combinations of prior pregnancy experiences of women (including nulligravidity), we showed that a history of prior childbirth (at term) with no preterm births gave the lowest risk of very preterm birth. With this group as the reference category, odds ratios of more than two were associated with all other prior reproductive histories. There was no evidence of difference in risk between types of abortion (i.e. spontaneous or induced) although the risk increased if a prior preterm birth had also occurred. There was an increasing risk of very preterm birth associated with increasing numbers of abortions. This method of data analysis reveals consistent and similar risks for very preterm birth following spontaneous or induced abortions. The findings point to the need to explore commonalities rather than differences in regard to the impact of abortion on subsequent births.     

Modelling sequence of prior pregnancies on subsequent risk of very preterm birth

Watson LF, Rayner J‐A, King J, Jolley D, Forster D, Lumley J. Modelling sequence of prior pregnancies on subsequent risk of very preterm birth. Paediatric and Perinatal Epidemiology 2010. The prevalence and intractability of preterm birth is known as is its association with reproductive history, but the relationship with sequence of pregnancies is not well studied. The data were from a population‐based case–control study, conducted in Victoria, Australia. The study recruited women giving birth between April 2002 and April 2004 from 73 maternity hospitals. Detailed reproductive histories were collected by interview a few weeks after the birth. The cases were 603 women having a singleton birth between 20 and <32 weeks gestation (very preterm births including terminations of pregnancy). The controls were 796 randomly selected women from the population having a singleton birth of at least 37 completed weeks gestation. Unconditional logistic regression was used to assess the association of very preterm birth with sequence of pregnancies defined by their outcome (prior abortion – spontaneous or induced, and prior preterm or term birth) with adjustment for sociodemographic factors. The outcomes of each prior pregnancy, stratified by pregnancy order, and starting with the pregnancy immediately before the index or control pregnancy, were categorised as one of abortion, preterm birth or term birth. We showed that each of these prior pregnancy events was an independent risk of very preterm birth. This finding does not support the hypothesis of a neutralising effect of a term birth after an abortion on the subsequent risk for very preterm birth and is further evidence for the cumulative or increasing risk associated with increasing numbers of prior abortions or preterm births.     

Adverse birth outcomes in United Republic of Tanzania--impact and prevention of maternal risk factors

OBJECTIVE: To determine risk factors for poor birth outcome and their population attributable fractions. METHODS: 1688 women who attended for antenatal care were recruited into a prospective study of the effectiveness of syphilis screening and treatment. All women were screened and treated for syphilis and other reproductive tract infections (RTIs) during pregnancy and followed to delivery to measure the incidence of stillbirth, intrauterine growth retardation (IUGR), low birth weight (LBW) and preterm live birth. FINDINGS: At delivery, 2.7% of 1536 women experienced a stillbirth, 12% of live births were preterm and 8% were LBW. Stillbirth was independently associated with a past history of stillbirth, short maternal stature and anaemia. LBW was associated with short maternal stature, ethnicity, occupation, gravidity and maternal malaria whereas preterm birth was associated with occupation, age of sexual debut, untreated bacterial vaginosis and maternal malaria. IUGR was associated with gravidity, maternal malaria, short stature, and delivering a female infant. In the women who had been screened and treated for syphilis, in between 20 and 34% of women with each outcome was estimated to be attributable to malaria, and 63% of stillbirths were estimated as being attributable to maternal anaemia. Screening and treatment of RTIs was effective and no association was seen between treated RTIs and adverse pregnancy outcomes. CONCLUSION: Maternal malaria and anaemia continue to be significant causes of adverse pregnancy outcome in sub-Saharan Africa. Providing reproductive health services that include treatment of RTIs and prevention of malaria and maternal anaemia to reduce adverse birth outcomes remains a priority.     

Ectopic pregnancy and prior induced abortion.

We compared the prior pregnancy histories of 85 multigravid women with an ectopic pregnancy and 498 multigravid delivery comparison subjects. We found a relationship between the number of prior induced abortions and the risk of ectopic pregnancy: the crude relative risk of ectopic pregnancy was 1.6 for women with one prior induced abortion and 4.0 for women with two or more prior induced abortions; however, use of multivariate techniques to control confounding factors reduced the relative risks to 1.3 (95 per cent confidence interval, 0.6-2.7) and 2.6 (95 per cent confidence interval, 0.9-7.4), respectively. The analysis suggests that induced abortion may be one of several risk factors for ectopic pregnancy, particularly for women who have had abortions plus pelvic inflammatory disease or multiple abortions.     

祥云县已婚育龄夫妇不良妊娠结局相关因素病例对照研究

目的:探讨已婚育龄夫妇不良妊娠结局发生的危险因素,为制定干预措施、实现优生优育提供依据。方法:随机选取67例不良妊娠结局已婚育龄夫妇,按照1∶1配对的原则选取67例正常妊娠结局的已婚育龄夫妇作对照,调查可能对两组已婚育龄夫妇不良妊娠结局有影响的相关因素,采用SPSS软件对所有调查因素进行单因素与多因素Logistic回归分析。结果:经Logistic回归模型进行单因素分析,有统计学意义的危险因素有已婚育龄夫妇的年龄(女:OR值=0.585,男:OR值=0.536)、受教育年限(女:OR值=2.982,男:OR值=2.811)、已婚育龄妇女是否曾经怀孕过(包括曾经非意愿流产、早产、不良妊娠结局以及正常分娩等,OR值=2.210)、丈夫的体重指数(OR值=0.370)、丈夫是否吸烟(OR值=11.400)以及丈夫现在是否戒烟(OR值=0.098)。经Logistic回归模型进行多因素分析,有统计学意义的危险因素有丈夫是否吸烟(OR值=8.313)、丈夫是否戒烟(OR值=0.082)。结论:已婚育龄夫妇的年龄、受教育年限、已婚育龄妇女是否曾经怀孕过(包括曾经非意愿流产、早产、不良妊娠结局以及正常分娩等)、丈夫的体重指数等均为不良妊娠结局的危险因素,并且再次证实了吸烟对不良妊娠结局的影响。劝阻丈夫吸烟、减少育龄妇女被动吸烟、控制婚育年龄、避免高龄妊娠、合理饮食以避免过重和肥胖均能够减少不良妊娠结局的发生。     

母亲孕期被动吸烟烟及父亲饮酒与低出生体重儿关系研究

目的：为进一步探索低出生体重儿发生的相关危险因素。方法：我们对沈阳市妇婴等15家医院分娩的部分产妇进行了低出生体重儿的病例对照研究。结果：在控制孕妇患慢性疾病、生殖器官的畸形、严重妊娠反应、文化程度、巨细胞病毒等感染以及主动吸烟等混杂因素后,孕期被动吸烟分娩出低出生体重儿的危险性为非被动吸烟的2.95倍,95%可信区间OR95%CI为2.07-4.21;丈夫饮酒史、自然流产、人工流产史、家族低体重史、孕前的BMI、孕期服用解热镇痛药物以及职业接触有机物均可能是低出生体重儿的危险因素。     

Low birth weight in relation to multiple induced abortions.

BACKGROUND. Most studies report that a single induced abortion does not increase risk for delivering a low birth weight infant in a subsequent pregnancy. However, the effect of multiple abortions has not been adequately evaluated. METHODS. This relationship was studied in 6541 White women who delivered their first child between 1984 and 1987. We compared the frequencies of low birth weight (less than 2500 g) among infants born to 1999 women without prior induced abortion and 1999 women with one abortion with the frequencies of low birth weight among infants born to women with two (n = 1850), three (n = 520), and four or more (n = 173) prior induced abortions. RESULTS. After adjustment for confounding variables, we found no linear relationship in risk of low birth weight among women with one (relative risk [RR] = 1.2, 95% confidence interval [CI] = 0.9-1.5), two (RR = 1.5, 95% CI = 1.1-2.0), three (RR = 1.3, 95% CI = 0.8-1.9), or four or more (RR = 1.6, 95% CI = 0.9-2.9) prior induced abortions. CONCLUSIONS. These findings confirm earlier reports of little or no evidence of harmful effects on birth weight by one or by two or more induced abortions. We further report that risk is not significantly elevated even in women with three, four, or more prior terminations of pregnancy when compared with women with one or two abortions.     

Evaluation of antenatal risk scoring in a preterm birth prevention and perinatal loss

The study aim was to determine risk factors associated with preterm delivery, perinatal mortality, and neonatal morbidity among 687 indigent, pregnant women in their first term registered with the New Civil Hospital, Ahmedabad, India, between September, 1989, and March, 1991. Women were scored according to their level of risk: no risk, mild risk, moderate risk, and severe risk, from scores based on sociodemographic and obstetric data: pallor, maternal weight, 2 or more prior abortions, first pregnancy or 5 pregnancies, adolescent pregnancy, prior preterm birth, prior prenatal mortality or stillbirths. Out of 696 deliveries, there were 71 (10.2%) preterm births, of which 3 (2.38%) were among women within the no risk groups. There were 47 (11.10%) from the mild risk group and 20 (14.08%) from the moderate risk group. There were 20% from the severe risk group. Perinatal mortality was 84.77/1000 births, and 7.94 among the no risk group. The perinatal mortality rate rose with level of risk, with 92.20 per thousand births for the mild risks to 200 for the severe risks, which was statistically significant. Neonatal morbidity also increased with the increased level of risk. Preterm birth was found not to be associated with pallor and prior history of stillbirth. Perinatal mortality was not associated with pallor and first pregnancy. Factors significantly associated with preterm births and perinatal mortality were maternal malnutrition, higher pregnancy order, older maternal age at delivery, and prior preterm births and fetal loss. Pregnant women with risk factors had greater relative risk of preterm birth and perinatal mortality by 5.01 and 13.09 times. With maternal risk factors, the risk increased by 80.05% and 92.35%. The risk factors were highly sensitive for preterm births (95.77%), but had low specificity (19.69%), and low positive predictive value (11.93%). Perinatal mortality sensitivity, specificity, and positive predictive values were 98.31%, 19.90%, and 10.34%n respectively. The findings differed from previously reported studies; scoring system used has a higher sensitivity to predicting preterm birth and perinatal mortality among high risk women, and poor sensitivity among low risk women. Moderate and mild could be identified with this system and referred for follow-up.     

Low birth weight in pregnancies following induced abortion: no evidence for an association

Compared with women delivering a first pregnancy, those delivering a second pregnancy after aborting the first have similar rates of low (less than 2,500 g) birth weight newborns (relative risk (RR) G2A1/G1 = 0.86, 95% confidence interval (CI) = 0.49-1.51) and mean birth weight (delta = 16.3 g, p = 0.63). Abortion of the first pregnancy prevents the reduction in low birth weight and increase in mean birth weight in the second pregnancy which delivery of the first pregnancy normally bestows (RR G2P1/G2A1 = 0.48, 95% CI = 0.25-0.90; delta = 135.3 g, p less than 0.0001). Two prior induced abortions do not significantly increase risk for low birth weight (RR G3A2/G1 = 1.14, 95% CI = 0.37-3.56) or decrease mean birth weight (delta = 29.0 g), compared with women delivering their first pregnancy. The second of two deliveries has a reduced risk of low birth weight irrespective of whether both deliveries follow an aborted first pregnancy. Adjustment for confounding factors did not materially change these results. Low birth weight rates were higher after abortions performed in hospital compared with elsewhere (p = 0.03), but mean birth weight was not affected. Gestation at abortion, vacuum aspiration or dilatation and curettage, and abortion complications were unrelated to birth weight of subsequent pregnancies. Pregnancies conceived within six months of a prior abortion or delivery had lower birth weight than if the antecedent pregnancy ended more than six months previously.