Low Prepregnancy Body Mass Index Research Articles

Low pre-pregnancy body mass index and risk of medically indicated versus spontaneous preterm singleton birth

Objective(s) There were three primary objectives of this study: (1) to estimate the risk of preterm and very preterm birth by severity of low pre-pregnancy body mass index (BMI), (2) to determine if the risk in preterm and very preterm birth by severity of low pre-pregnancy BMI differs for spontaneous versus medically indicated preterm delivery, and finally (3) to determine if there is a difference in the risk for preterm and very preterm birth by severity of low pre-pregnancy BMI across gradations of gestational weight gain. Study design This study utilized the Missouri maternally linked cohort files from 1989 to 1997. After restricting analyses to singleton live births (gestational age 20–44 weeks) and women with either a low or normal BMI, the final study population consisted of 437,403 births. Pre-pregnancy BMI was categorized as normal (19.5–24.9), mild thinness (17.0–18.5), moderate thinness (16.0–16.9) and severe thinness (≤15.9). Statistical analyses included chi-square tests and logistic regression with generalized estimating equations (GEE). Results Underweight mothers were more likely to experience a preterm delivery. For all preterm births, the risk among underweight mothers increased with ascending underweight severity ( p < 0.01). Higher risk estimates were observed for spontaneous than for medically indicated preterm birth. For each BMI category, extreme risk values for spontaneous preterm births were observed among women with very low gestational weight gain (<0.12 kg/week). Severely thin mothers with very low and very high pregnancy weight gain were at the greatest risk for spontaneous preterm birth. By contrast, underweight women with moderate gestational weight gain (0.23–0.68 kg/week) had the lowest risk for spontaneous preterm birth with the sole exception of moderately underweight gravidas. Conclusions These findings suggest that women with low or normal pre-pregnancy BMI should be counseled to maintain a moderate level of gestational weight gain (0.23–0.68 kg/week) in order to reduce their risk for preterm birth. Further, our observation that severity of low pre-pregnancy BMI was associated directly (in a dose–response pattern) with preterm birth highlights the importance of preconceptional counseling for women—specifically the importance of women achieving or maintaining a normal weight status prior to pregnancy.

Maternal Characteristics and Outcomes Associated with Late Enrollment for Care in Teenage Pregnancies

To identify characteristics associated with late prenatal care in adolescent mothers. This retrospective cohort study reviews all nulliparous adolescent deliveries at the authors' institution during 2000-2004. Subjects were divided into three trimester groups using American College of Obstetricians and Gynecologists standard definitions. First trimester enrollees served as controls. Second and third trimester registrants served as exposure groups. Frequencies and odds ratios were calculated for adverse outcomes. During the study period, 484 adolescents met the inclusion criteria (11-18 years old). Very young adolescents (age <16 years) enrolled for care significantly later than their older counterparts (19.7 vs 16.2 weeks). Second trimester enrollment was not associated with any adverse outcomes. Third trimester registrants had significantly lower prepregnancy body mass index (23.2 vs 25.0 kg/m2) and weight gain (27.6 vs 32.6 lbs); and a higher rate of Medicaid use (77 vs 59%) and low birth weight infants (adjusted OR, 2.15; 95% CI, 1.04-4.43) when compared to controls. Third trimester enrollment for prenatal care in adolescents is associated with higher rates of adverse perinatal outcomes. Interventions to improve prenatal care enrollment among adolescents should be sought.

Pre-Pregnancy Body Mass Index among Pregnant Adolescents: Gestational Weight Gain and Long-Term Post Partum Weight Retention

Study Objective To determine the relationship between adolescents' pre-pregnancy body mass index (BMI), and gestational weight gain and postpartum weight retention. Design We review the medical records of adolescents participating in a prospective cohort study on comprehensive health care and parenting education to determine pre-pregnancy BMI, gestational weight gain, and postpartum weight retention at one year. Setting Urban academic hospital clinic. Participants 102 pregnant adolescents aged 15–21 years. Main Outcomes Gestational weight gain and weight retention at one year postpartum. Results and Conclusions Fifty-two (51%) adolescent women had normal pre-pregnancy BMI according to the Institute of Medicine classification. Adolescent women with normal (36.5%) and high pre-pregnancy BMI (66.5%) were more likely than women with low pre-pregnancy BMI (26.5%) to exceed recommended gestational weight gain. Adolescent women who exceeded recommended weight gain retained significantly more weight at 1 year postpartum than women with weight gain within or below the recommendation. In a linear regression model that controlled for age, smoking, pregnancy complication, and post partum contraceptive use, pre-pregnancy BMI and gestational weight gain were the strongest predictors of postpartum weight retention at 1 year. A normal to high pre-pregnancy BMI and excessive gestational weight gain are important predictors of postpartum weight retention in adolescents. These two predictors must be monitored systematically with the aim of preventing postpartum obesity and its associated diseases among this population.

Risk factors for small for gestational age

The purpose of the paper was to determine the risk factors for small-for-gestational-age (SGA) infants at full term, in Japan. The study was conducted at four hospitals and clinics in the Tokyo metropolitan area. A retrospective review of 2972 mothers and their infants born from singleton pregnancies at any time during the years 2002 and 2003 was conducted. Of these women, 8.4% gave birth to SGA infants. The proportion of SGA infants was significantly higher among heavy smokers (>10 cigarettes/day; 13.7%, P < 0.01). The odds ratio (OR) for SGA decreased significantly in proportion to the pregnancy body mass index (OR, 0.89; 95% confidence interval [CI]: 0.84-0.94, P < 0.001). The OR of SGA for stratified maternal weight gain was 1.79 (95%CI: 1.24-2.58, P </= 0.01) for weight gain < 8.0 kg; 1.16 (95%CI: 0.79-1.71, P = 0.45) for weight gain 8.0-10.0 kg; and 0.49 (95%CI: 0.3-0.78, P < 0.01) for weight gain >12 kg. The present study clearly confirms the detrimental effect of a low prepregnancy body mass index, low maternal weight gain and maternal smoking during pregnancy on the incidence of SGA infants.

Are Babies Born to Short, Primiparous, or Thin Mothers “Normally” or “Abnormally” Small?

To examine whether the smaller size of infants born to primiparous, short, or thin mothers is associated with increased risks of perinatal mortality. We compared gestational age-specific patterns of "revealed" small-for-gestational-age (SGA) birth (number of SGA births expressed as a proportion of fetuses remaining in utero at each gestational age) with the patterns for perinatal mortality among singleton late fetal deaths and live births (n = 791,523) to Swedish mothers in 1992 to 2001. Based on a single standard for SGA, primiparae were at substantially higher risk of revealed SGA throughout gestation, paralleling the pattern for perinatal mortality. However, for short and thin women, risks of revealed SGA were much more consistent with those for perinatal mortality when SGA was based on height-specific or body mass index-specific standards, respectively, rather than on the single standard. Overweight and obese mothers had lower revealed SGA rates based on either standard but higher perinatal mortality rates. Slower fetal growth due to maternal short stature or low prepregnancy body mass index appears to be physiologic, whereas the slower growth of fetuses born to primiparous women is associated with higher risks of perinatal death.

Risk factors for first trimester miscarriage—results from a UK‐population‐based case–control study

The aim of this study was to examine the association between biological, behavioural and lifestyle risk factors and risk of miscarriage. Population-based case-control study. Case-control study nested within a population-based, two-stage postal survey of reproductive histories of women randomly sampled from the UK electoral register. Six hundred and three women aged 18-55 years whose most recent pregnancy had ended in first trimester miscarriage (<13 weeks of gestation; cases) and 6116 women aged 18-55 years whose most recent pregnancy had progressed beyond 12 weeks (controls). Women were questioned about socio-demographic, behavioural and other factors in their most recent pregnancy. First trimester miscarriage. After adjustment for confounding, the following were independently associated with increased risk: high maternal age; previous miscarriage, termination and infertility; assisted conception; low pre-pregnancy body mass index; regular or high alcohol consumption; feeling stressed (including trend with number of stressful or traumatic events); high paternal age and changing partner. Previous live birth, nausea, vitamin supplementation and eating fresh fruits and vegetables daily were associated with reduced risk, as were feeling well enough to fly or to have sex. After adjustment for nausea, we did not confirm an association with caffeine consumption, smoking or moderate or occasional alcohol consumption; nor did we find an association with educational level, socio-economic circumstances or working during pregnancy. The results confirm that advice to encourage a healthy diet, reduce stress and promote emotional wellbeing might help women in early pregnancy (or planning a pregnancy) reduce their risk of miscarriage. Findings of increased risk associated with previous termination, stress, change of partner and low pre-pregnancy weight are noteworthy, and we recommend further work to confirm these findings in other study populations.

Weight Gain and Spontaneous Preterm Birth

To study how the relationship between gestational weight gain and spontaneous preterm birth interacts with maternal race or ethnicity and previous preterm birth status. This was a retrospective cohort study of singleton births to women of normal or low prepregnancy body mass index. Gestational weight gain was measured as total weight gain divided by weeks of gestation at delivery, and weight gain was categorized as low (less than 0.27 kg/wk,), normal (0.27-0.52 kg/wk), or high (more than 0.52 kg/wk). Univariable and multivariable analyses were performed on the relationship between weight gain categories and spontaneous preterm birth, stratified by maternal race or ethnicity and history of previous preterm birth. Overall, low weight gain was associated with spontaneous preterm birth (adjusted odds ratio [AOR] 2.5, 95% confidence interval [CI] 2.0-3.1). Although low gain was consistently associated with increased spontaneous preterm birth, some differences were found in subgroup analysis. Among African Americans with a previous preterm birth, both low and high weight gain were associated with increased odds of spontaneous preterm birth (AOR for low weight gain 4.3, 95% CI 1.2-15.5; AOR for high weight gain 6.1, 95% CI 1.8-20.2). For all other groups, high weight gain was not associated with spontaneous preterm birth. Among Asians with a previous preterm birth, low weight gain was not statistically significantly associated with spontaneous preterm birth (AOR 1.9, 95% CI 0.5-7.7). Among Asians there was also a non-statistically significant inverse relationship between high weight gain and spontaneous preterm birth (AOR 0.5, 95% CI 0.3-1.1). These results confirm an association between low maternal weight gain and spontaneous preterm birth. The effect modification of maternal race or ethnicity and history of previous preterm birth on this association deserves further study. II-2.

Maternal anthropometry and pregnancy outcomes: a proposal for the monitoring of pregnancy weight gain in outpatient clinics in South Africa

The aim of this review was to develop a framework for the monitoring of pregnancy weight gain in South African outpatient clinics. Studies showed that intrauterine malnutrition have more serious consequences for children than postnatal malnutrition. Undernutrition, as well as overnutrition during pregnancy, was associated with adverse pregnancy outcomes. The IOM published recommended weight gains by pre-pregnancy body mass index (BMI). Wasting in pregnant women can be defined as a mid-upperarm circumference (MUAC) < 22cm. Low prepregnancy BMI is considered a risk factor for preterm birth and intra-uterine growth retardation. Pregnant women in developing countries start to attend antenatal clinics late in pregnancy, so that prepregnancy BMI may be unknown and antenatal care can be based on pregnancy weight gain only. A framework is proposed that identifies the critical points for action during pregnancy to improve birth outcomes. Health care providers should measure height, weight and MUAC and try to classify pregnant women according to weight status, set weight gain goals and monitor gestational weight gain between follow-up visits. Women with short stature (< 145cm), low body weight (< 45kg), and/or MUAC < 22cm are considered to be at risk of adverse pregnancy outcomes. Weekly weight gains should range from 0.3kg for overweight women to 0.5kg or more for underweight women from the second trimester. Genetic background, age, general health, HIV and educational status, cigarette smoking, past nutritional status of the mother, parity, multiple pregnancies, climate, socioeconomic conditions and the availability of health services should be adjusted for in statistical analyses.

Body Mass Index, Provider Advice, and Target Gestational Weight Gain

To study the relationships among prepregnancy body mass index (BMI), women's target gestational weight gain, and provider weight gain advice. Project WISH, the acronym for Women and Infants Starting Healthy, is a longitudinal cohort study of pregnant women in the San Francisco Bay area. We excluded subjects with preterm birth, multiple gestation, or maternal diabetes. Among overweight women (prepregnancy BMI 26.1-29.0), 24.1% reported a target weight gain above the Institute of Medicine (IOM) guidelines, compared with 4.3% of normal weight women (P < .001). Among women with a low prepregnancy BMI (< 19.8), 51.2% reported a target weight gain below the guidelines, compared with 10.4% of normal weight women (P < .001). These patterns persisted in a multivariate analysis. Latina ethnicity, lower maternal education, low prepregnancy BMI (< 19.8), lack of provider advice about weight gain, and provider advice to gain below guidelines were all independently associated with a target weight gain below IOM guidelines. Prepregnancy BMI more than 26, multiparity, lower age, and provider advice to gain above guidelines were all associated with a target gain above IOM guidelines. Women's beliefs about the proper amount of weight gain and provider recommendations for weight gain vary significantly by maternal prepregnancy BMI. Many women report incorrect advice about gestational weight gain, and women with high or low prepregnancy BMI are more likely to have an incorrect target weight gain. New approaches to provider education are needed to implement the IOM guidelines for gestational weight gain.

Characteristics and risk factors for adverse birth outcomes in pregnant black adolescents

Objectives To describe maternal characteristics and birth outcomes in a group of pregnant minority adolescents and to characterize the impact of maternal age (<15 years versus 15-17 years) on birth outcomes. Study design A 10-year retrospective chart review was conducted in 1120 pregnant black adolescents (≤17 years of age) who had received prenatal care at an inner-city maternity clinic in Baltimore, Md. Results Pregnant black adolescents had a higher incidence of low birth weight infants, preterm delivery, and fetal death compared with normative data from the United States. Younger adolescents were more likely to have inadequate utilization of prenatal care ( P<.01). Older adolescents had a higher incidence of gonorrhea infections ( P = .046), greater rates of self-reported substance abuse ( P = .063), and a higher history of cigarette smoking ( P<.01). Low prepregnancy body mass index (BMI), inadequate weight gain, and poor prenatal care utilization were strong independent predictors of preterm birth ( P<.05). Low prepregnancy BMI, inadequate weight gain, female infant, and self-reported cigarette smoking history were significantly associated with decreased infant birth weight ( P<.05). Conclusions Pregnant black adolescents had increased risks of adverse pregnancy outcomes. This population should be studied further to develop age-appropriate and population-specific interventions to improve birth outcomes.

Some Thoughts on Body Mass Index, Micronutrient Intakes and Pregnancy Outcome

A low prepregnancy body mass index is one of strongest predictors of adverse pregnancy outcomes such as preterm birth and fetal growth retardation. A low body mass interacts with other risk factors such as smoking and stress to increase risk of these outcomes, whereas zinc supplementation and low-dose aspirin increase birth weight in thin but not normal-size women. The association between maternal thinness and adverse pregnancy outcomes may be mediated more by a low plasma volume than by decreased protein or energy status. Maternal micronutrient status may partially mediate plasma volume expansion in pregnancy. Therefore, improving maternal micronutrient status may reduce adverse outcomes through this mechanism.

The Epidemiology of Adverse Pregnancy Outcomes: An Overview

This paper provides an overview of the occurrence, etiology and temporal trends of adverse pregnancy outcomes. Disparities between developed and developing countries are highlighted for maternal mortality, infant mortality, stillbirth and low birth weight. The higher rate of low birth weight in developing countries is primarily due to intrauterine growth restriction rather than preterm birth. Much of the excess intrauterine growth restriction is caused by short maternal stature, low prepregnancy body mass index and low gestational weight gain (due to low energy intake). No important contribution has been established for micronutrient intake, nor have different fetal growth trajectories been demonstrated to reflect the timing of exposure to nutritional or other etiologic factors. Infant mortality has declined substantially over time both in developed and developing countries despite no decline (and even an increase) in low birth weight. Several developed countries have reported a temporal increase in fetal growth in infants born at term, a reduction in stillbirth rates and prevention of neural tube defects. More progress is required, however, in understanding the etiology and prevention of preterm birth.

Maternal prenatal lifestyle factors and infectious disease in early childhood: a follow-up study of hospitalization within a Danish birth cohort.

To examine whether maternal prenatal lifestyle factors were associated with the risk of hospitalization with infectious disease during early childhood and whether a possible association was modified by fetal growth reduction. The study was based on a birth cohort of 10 400 newborns whose mothers attended the midwife centers in Odense and Aalborg, Denmark, from April 1984 to April 1987 at approximately the 36th week of gestation. Information on hospitalization with infectious disease was extracted from the National Hospital Discharge Registry, and newborns were followed up to the end of 1996. Among 6022 children who were hospitalized at least once, 31.4% (n = 1892) were hospitalized with infectious diseases. The cumulative incidence rate of hospitalization with infections in children from the age of 6 months to 12 years was 18.9%. The incidence rate ratio in children born to mothers smoking during pregnancy was 1.24 (95% confidence interval: 1.13-1.36) compared with those of nonsmoking mothers. Mothers whose body mass index was <18 kg/m(2) were more likely to give birth to infants who were hospitalized with infectious disease (incidence rate ratio: 1.29; 95% confidence interval: 1.05-1.59). The increased risk was present in children only up to the age of 5 years. The study shows that maternal smoking during pregnancy and a low prepregnancy body mass index are associated with a higher risk of hospitalization with infectious disease during early childhood. These associations are independent of fetal growth indicators.

A Low Prepregnancy Body Mass Index Is a Risk Factor for an Offspring with Gastroschisis

A mother's prepregnancy obesity has been suggested as a risk factor for having offspring with an abdominal wall defect. We evaluated this hypothesis among 104 cases of gastroschisis--a severe birth defect of the abdominal wall most prevalent in infants of young women--and 220 controls with no defect. Using Quetelet's index (QI = weight in kg/height in m2) as a measure of body mass, we found a higher risk of gastroschisis (odds ratio (OR) = 3.2; 95% confidence interval (CI) = 1.4-7.3) for underweight mothers (QI<18.1 kg/m2) and a lower risk (OR = 0.2; 0.05-0.9) for overweight mothers (QI>28.3 kg/m2) as compared with mothers of normal weight. As QI was correlated to height, with the correlation varying according to mother's ethnicity and age, we adjusted for these factors in the analysis; the adjusted values approximated the unadjusted values. Evaluation of QI as a continuous variable showed that, for every unit increase in QI, the risk for gastroschisis decreased by about 11%. Sociodemographic, pregnancy, and nutrient factors did not confound the association. These results suggest that low prepregnancy body mass rather than obesity is a risk factor for gastroschisis.

Low prenatal weight gain among adult WIC participants delivering term singleton infants: variation by maternal and program participation characteristics.

To determine the association of maternal and prenatal WIC program participation characteristics with low prenatal weight gain among adult women delivering liveborn, singleton infants at term. WIC program data for 19,017 Black and White Alabama women delivering in 1994 were linked with birth certificate files to examine the association of anthropometric, demographic, reproductive, hematologic, behavioral and program participation characteristics with low prenatal weight gain. One third (31.0%) had low prenatal weight gain as defined by the Institute of Medicine. The incidence of low weight gain was increased among women who had < 12 years of education, were single, Black, anemic, had low or normal prepregnancy body mass index (BMI), increased parity, interpregnancy intervals < or = 24 months, used tobacco or alcohol, or entered prenatal care or WIC programs after the first trimester. After adjusting for selected maternal characteristics, the adjusted odds ratios (AOR) for low weight gain were increased with short interpregnancy intervals (AOR 1.21 to 2.20); tobacco use (AOR 1.16 to 1.40), anemia (AOR 1.20 to 1.25), and second trimester entry into prenatal care (AOR 1.14 to 1.20); the size of the AORs and 95% confidence intervals varied by BMI and racial subgroup. The results of this study suggest that WIC interventions targeting low prenatal weight gain be focused on risk factors present not only during pregnancy, but during the pre- and interconceptional periods as well. Interventions should target low BMI, tobacco use, and anemia, and include attention to nutrition screening and risk reduction among women in postpartum and family planning clinic settings.

Preterm and term births of small for gestational age infants: a population-based study of risk factors among nulliparous women.

To study risk factors for small for gestational age (SGA) infants by gestational age among nulliparous women and to estimate mortality rates among SGA and appropriate-for-gestational-age (AGA) infants by gestational age. A population-based study from the Swedish Medical Birth Register. Setting Sweden 1992 1993. Liveborn singleton infants to nulliparous women (n = 96,662). Crude and adjusted odds ratios of risk factors for SGA by gestational age. Rates of neonatal and postneonatal mortality. Older maternal age (> or = 30 years) was foremost associated with increased risks of very and moderately preterm SGA (> or = 32 weeks and 33-36 weeks, respectively), but also with term SGA (> or = 37 weeks). Risks of SGA increased with decreasing maternal height at all gestational ages. Smoking increased the risks of moderately preterm and term SGA. Short maternal education increased the risk of preterm SGA and low pre-pregnancy body mass index slightly increased the risk of term SGA. Pre-eclampsia and essential hypertension foremost increased the risk of very preterm SGA (OR = 40.5 and 32.4, respectively) and moderately preterm SGA (OR = 17.4 and 10.6, respectively), but also increased the risk of term SGA. Neonatal and postneonatal mortality rates of SGA infants were substantially influenced by gestational age, and mortality rates were consistently higher among preterm SGA infants compared with AGA infants. Risk factors for SGA and mortality rates among SGA infants vary by gestational age. A subdivision of risk factors by gestational age adds knowledge, particularly about risks of preterm SGA, where the highest rates of mortality were observed.

Risk for spontaneous preterm delivery by combined body mass index and gestational weight gain patterns

To investigate whether maternal anthropometric factors interact with one another or with other risk factors, thus modifying the risk of spontaneous preterm delivery. We carried out a case-control study of 230 spontaneous preterm births with intact membranes between 24 and 35 weeks gestation and 460 control term births. All the patients had prenatal care at the same institution. Logistic regression analysis was used to test for possible interactions adjusting for potential confounders. A pre-pregnancy body mass index < or = 19.5 Kg/m2 (odds ratio (OR) = 1.68, 95% confidence interval (CI) = 1.20-2.38) and a rate of weight gain < or = 0.37 Kg/week during the second and third trimesters (OR = 2.4, 95% CI = 1.69-3.42) were associated with an increased risk of spontaneous preterm delivery. The risk of spontaneous preterm delivery associated with a low second/third trimester weight gain was greater among patients with a body mass index < or = 19.5 (OR = 5.63, 95% CI = 2.35-13.8) compared to those with a body mass index > 19.5 (OR = 2.45, 95% CI = 1.60-3.75, adjusted p value for interaction = 0.05). The risk of spontaneous premature delivery associated with a maternal pre-pregnancy weight < or = 48 Kg was higher among smokers (OR = 5.81, 95% CI = 1.60-22.9) than among non-smokers (OR = 2.4, 95% CI = 1.53-3.74, adjusted p value for interaction = 0.05). The risk of spontaneous preterm delivery associated with a low pre-pregnancy body mass index is greater among patients with low rate of gestational weight gain during the second and third trimesters compared to those with a higher rate. The results of this study support the recommendation for increased rates of weight gain to patients with low body mass index compared to those with a higher body mass index.

Trends in pregnancy weight gain within and outside ranges recommended by the Institute of Medicine in a WIC population.

To examine the proportion of women with a pregnancy weight gain below, within, and above ranges recommended by the Institute of Medicine from 1990 to 1996. Our study population included women attending Special Supplemental Nutrition Program for Women, Infants and Children (WIC) clinics in five states who delivered a liveborn singleton infant at term (N = 120,531). Pregnancy weight gain was self-reported at the postpartum visit. Only 34% of women gained weight within recommended ranges and there was little change in this proportion from 1990 to 1996. The proportion of women gaining less than their recommended weight decreased from 23.4% to 22.0%, and the proportion gaining more than recommended increased from 41.5% to 43.7% during the study period. Stratified analyses revealed similar trends within all race-ethnicity, age, parity, trimester of WIC initiation, and trimester of prenatal care initiation strata and among women in low, average, and high prepregnancy body mass index categories. There was no change in the weight gain distribution among obese women. Absolute and relative increases in the proportion of women gaining more weight than recommended were greatest among women who were underweight, Asian or Native American, less than 20 years of age, multiparous, and who initiated WIC and prenatal care in the third trimester. Pregnancy weight gain increased among this population of WIC participants from 1990 to 1996.

Maternal anthropometry and idiopathic preterm labor

To assess the etiologic role of maternal short stature, low pre-pregnancy body mass index (BMI), and low rate of gestational weight gain in idiopathic preterm labor. We carried out a three-center case-control study of 555 women with idiopathic onset of preterm labor (before 37 completed weeks), including two overlapping (ie, nonmutually exclusive) subsamples: cases with early preterm labor (before 34 completed weeks) and cases with recurrent preterm labor (before 37 completed weeks plus a history of prior preterm delivery or second-trimester miscarriage). Controls were matched to cases by race and smoking history. All subjects responded in person to questions about height, pre-pregnancy weight, gestational weight gain, and obstetric and sociodemographic histories. Maternal height, pre-pregnancy weight, and gestational weight gain demonstrated excellent test-retest reliability, with intra-class correlation coefficients of 0.97, 0.99, and 0.91, respectively. Based on matched analyses, women with a height of 157.5 cm or less had an increased risk of idiopathic preterm labor (odds ratio [OR] 1.85, 95% confidence interval [CI] 1.25-2.74), as did those with a pre-pregnancy BMI less than 19.8 kg/m2 (OR 1.63, 95% CI 1.09-2.44) or a gestational weight gain rate less than 0.27 kg/week (OR 1.74, 95% CI 1.16-2.62). Conditional logistic regression models containing all three anthropometric variables and controlling for parity, marital status, language, age, and education yielded virtually identical point estimates and CIs. Maternal short stature, low pre-pregnancy BMI, and low rate of gestational weight gain may lead to shortened gestation by increasing the risk of idiopathic preterm labor.

Risk Factors for Abruptio Placentae

The authors studied the relation of sociodemographic, medical, and life-style factors and abruptio placentae in a large cross-sectional data base. The 143 cases of abruption identified in the Delivery Interview Program, conducted in Boston from 1977 to 1980, were compared with 1,257 randomly selected controls. The authors used multiple logistic regression techniques to derive maximum likelihood estimates of the adjusted odds ratios and 95% confidence intervals as measures of the association between exposure factors and abruption. A history of chronic hypertension was associated with a threefold increase in risk (odds ratio (OR) = 3.1, 95% confidence interval (Cl) 1.1-8.4), but pregnancy-induced hypertension was not associated with abruption. Excess risk was associated with advanced maternal age (OR = 2.3, 95% Cl 1.3-3.9), low prepregnancy body mass index (OR = 2.3, 95% Cl 1.3-4.1), a history of prior stillbirth (OR = 3.5, 95% Cl 1.8-7.0), and at least weekly use of marijuana during pregnancy (OR = 2.8, 95% Cl 1.2-6.6). Overall, the association with cigarette smoking during pregnancy was of only borderline significance (OR = 1.5, 95% Cl 1.0-2.2), although there appeared to be a dose-response relation between the number of cigarettes smoked and risk of abruption.