The effects of exercise on birth weight: a meta-analysis
Eddie T.C. Lam
Abstract: Previous research regarding the effects of exercise on pregnancy outcomes has been inconsistent. The purpose of this study was to adopt an objective research technique, meta-analysis, to summarize and analyze different studies with controversial results. Three coding variables (i.e., exercise duration, pre-pregnancy weight, and age) were selected in this study for comparisons. Though the effect size (ES) of the pregnant mothers who exercised under 30 minutes was greater than that of those who exercised between 30 and 60 minutes, the overall ES (-107.838, 95% CI = -482.93 to 267.26) indicated no significant birth weight differences between the two groups. On the whole, the results of this study support the notion that a significant positive relationship exists between birth weight and the pre-pregnancy weight. However, regression analysis indicated that a significant p <. 05) positive relationship existed between birth weight and the pre-pregnancy weight of the pregnant mothers (R =.75, p =.04). The conclusions of this study should be cautiously interpreted since they are limited to the selected studies under investigation. Directions and recommendations for future research are discussed.
Physiological factors such as cardiac output, oxygen consumption, hormones, etc. will alter when a person exercises. Such physiological variables also change during pregnancy (Bell & O’Neill, 1994; Gorski, 1985; Spatling, Fallenstein, Huch, Huch, & Rooth, 1992). The combined effects of exercise during pregnancy are a major concern for most medical care providers, educators, the general public, as well as pregnant women and their families. The most common question being raised is whether oxygen and nutrients are shunted from the uterus to the working muscles during exercise. As a consequence, will women deliver immature or underweight babies because of exercise activity during pregnancy?
Previous research studies have indicated that low birth weight (i.e., not more than 2500 g) babies were inferior to normal weight babies in reference to future growth and development. There appears to be a higher frequency of learning disabilities and behavioral problems (McCormick, Gortmaker, & Sobol, 1990; Ornstein, Ohlsson, Edmonds, & Asztalos, 1991; Sommerfeldt, Ellersten, & Markestad, 1996; Sommerfeldt, Troland, Ellersten, & Markestad, 1996; Szatmari, Saigal, Rosenbaum, Campbell, & King, 1990), lower Intelligence Quotient (Ornstein, Ohlsson, Edmonds, & Asztalos, 1991; Pharoah, Stevenson, Cooke, & Stevenson, 1994; Sommerfeldt, Ellersten, & Markestad, 1995), and motor clumsiness such as impaired balance (Largo et al., 1989; Marlow, Roberts, & Cook, 1989) among low birth weight babies.
The direct causes of low birth weight babies are not fully understood. However, many factors have been examined to determine their effects on pregnancy outcomes. These factors include supplements (e.g., Scholl & Johnson, 2000), nutrition (e.g., Breslin, 1998), and exercise (see Pivarnik, 1998 and Sternfeld, 1997 for a thorough review). Among these factors, the most controversial one seems to be the effects of exercise on pregnancy outcomes, particularly on the changes in birth weight. In their study, Bell, Palma, and Lumley (1995) compared women who were doing vigorous exercise prior to pregnancy and continued exercising during pregnancy with those who did not do regular vigorous exercise (controls). They found women who did more than 4 sessions (30 minutes each session) of vigorous exercise weekly at 25 weeks gestation had babies whose mean birth weight was 315g lower than their counterparts. Other studies also supported the idea that strenuous physical activity in pregnancy could be associated with low birth weight and earlier deliveries (Bell & O’Neill, 1994; Clapp & Dickstein, 1984).
Researchers also indicated that a number of other factors seem to be related to poor pregnancy outcomes, as well. These factors may include, but are not limit to, the following: (a) maternal weight prior and during pregnancy (e.g., Cnattingius, Bergstrom, Lipworth, & Kramer, 1998; Edwards, Hellerstedt, Alton, Story, & Himes, 1996; Kumari, 2001; Ogunyemi, Hullett, Leeper, & Risk, 1998), (b) maternal nutrition, such as nutrient deficiencies or toxicities, use of some herbal supplements, eating disorders (e.g., Brown & Kahn, 1997; Story & Alton, 1995), (c) socioeconomic issues, like poverty, low levels of education, limited availability of food (e.g., Jonas, Roder, & Chan, 1992; Otterblad-Olausson, Cnattingius, ex: Goldenberg, 1997), (d) lifestyle choices, such as smoking, alcohol or other drug use (e.g., Kallen, 2001; Korea, Pastuszak, & Ito, 1998), (e) age, for example, teens and women over age 35 (e.g., Gortzak-Uzan, Hallak, Press, Katz, & Shoham-Vardi, 2001; Seoud et al., 2002), (f) previous pregnancies, such as short intervals between pregnancies, poor prior pregnancy outcomes, multiple births (e.g., Meyer, Buescher, & Surles, 1999; Zhu, Haines, Le, McGrath-Miller, & Boulton, 2001), and (g) maternal health concerns, like high blood pressure, diabetes, or other chronic diseases (e.g., Lopez, Smith, & Gutierrez, 2002; Sibai, 1996; Xiong, Demianczuk, Saundersm, Wang, & Fraser, 2002).
Pivarnik, Mauer, Ayres, Kirshon, Dildy, and Cotton (1994), however, compared nine aerobically trained, physically active pregnant women who continued to exercise throughout gestation with five healthy yet sedentary pregnant women. They concluded that average birth weight and length of gestation did not significantly differ between the subject groups. Sternfeld, Quesenberry, Eskenazi, and Newman (1995) investigated the effect of different aerobic exercise levels on pregnancy outcomes with 388 women between the ages of 18 and 42 and found that exercise levels were not associated with mean birth weight and other pregnancy outcomes. Several other studies also indicated that physical activity was not associated with changes in birth weight (Dale, Mullinax, & Bryan, 1982; Jarrett & Spellacy, 1983; Rice & Fort, 1991; Rose, Haddow, Palomake, & Knight, 1991).
Conversely, after assessing 800 prenatal patients, Hatch et al. (1993) asserted that in fit and low-risk patients, exercise was positively related to fetal growth. They indicated that low to moderate exercise level patients had a mean birth weight about 100 g higher than the non-exercisers. In addition, large birth weight increments (about 300 g) were found for those who exercised throughout pregnancy at levels approximating 3,000 Kcal per week. Similarly, Brodey (1993) also concluded that pregnant women who expended up to 1,000 Kcal a week doing both high and low impact activities (e.g., stationary biking, aerobics, jogging, and strength training) delivered babies who weighed 5% more than those by the sedentary mothers. Comparatively, mothers who expended 2,000 Kcal a week delivered babies weighing 10% more (Brodey, 1993). Likewise, Johnson et al. (1994) demonstrated that exercise was associated with higher mean birth weight and head circumference in African American pregnant women.
Because of the controversy in these studies regarding the effects of maternal exercise on birth weight, there is a need to quantitatively and objectively summarize the findings of related studies. The purpose of this paper was to summarize and analyze studies regarding maternal exercise and birth weight using meta-analysis (Glass, 1977; Hedges & Olkin, 1985). Meta-analysis is a strategy that statistically analyzes summary findings of empirical research (Glass, 1977). Hedges and Olkin (1985) described meta-analysis as “the rubric used to describe quantitative methods for combining evidence across studies” (p. 13).
The outcome of the meta-analysis is derived from four steps. First, evaluations relevant to a specific topic are collected. Secondly, specific features of these evaluations are described quantitatively. Next, outcomes are formulated into a common measure called the effect-size, the standardized difference between the experimental and the control groups on a specific criterion. Finally, the researcher utilizes statistical methods to find relations between study features and study outcomes (Bangert-Drowns, 1986). Since meta-analysis usually relies on “data” in the form of summary statistics derived from the primary analyses of studies, it can be regarded as an analysis of the results of statistical analyses (Hedges &-Olkin, 1985).
All of the research articles selected for this study were based on a literature exploration using (a) computer and (b) hand search techniques. The computer search was restricted to the following databases: Medline, ProQuest Direct, PsycINFO, ERIC, SPORT Discuss, and Books & Dissertations. The hand search was based on the references listed in journal articles and books/dissertations. The key words used for computer search were exercise, pregnancy, pregnancy outcome’, and `birth weight’. According to the afore-said procedures in the literature search, 40 articles were identified to be related to the topic under investigation and appropriate for initial review. A majority of the articles came from Medline, while ERIC provided the least number of articles. After a thorough examination of the 40 articles, 31 of them did not meet the criteria for this study because one or more of the following criteria were missing: (a) standard deviation, e.g., Dale, Mullinax, & Bryan, 1982; Hall & Kaufmann, 1987, (b) sample size, e.g., Clapp, 1996, (c) control group, e.g., Jarrett & Spellacy, 1983, or (d) other reasons such as using animals as subjects (e.g., Matsuno, Esrey, Perrault & Koski, 1999). As a result, only nine studies that met the criteria for meta-analysis were selected.
In this study, nine studies were examined to determine the effects of exercise duration on birth weight. To meet the criteria to be included in this meta-analysis, all of the following elements needed to be present in a study: (a) use birth weight as the dependent variable, (b) provide sample size, mean and standard deviation for each group; if not, provide values of the F ratio or [c.sup.2] with degrees of freedom, and (c) have acceptable measurement quality, e.g., the use of a control group. Because the purpose of this study was to examine the effects of exercise on birth weight, exercise duration was selected as the coding variable. Two other variables of interest, pre-pregnancy weight and age, which might potentially influence the effect sizes also were coded. Due to the limited number of studies, exercise duration was divided into two levels: (a) those who exercised up to but not more than 30 minutes, and (b) those who exercised between 30 and 60 minutes. The total sample size of the nine articles used for this study was 951.
The MetaWin Verson 2.0 (Rosenberg, Adams, & Gurevitch, 2000) computer program was used to examine (a) the differences of birth weight, age, and pre-pregnancy weight between the exercise group and control group, and (b) the effect size of birth weight between pregnant mothers who exercised less than 30 minutes versus those who exercised between 30 and 60 minutes. In addition, linear regression analyses were used to examine (a) the relationship between birth weight and age as well as pre-pregnancy weight of the experimental group, and (b) the relationship of age and pre-pregnancy weight differences between the experimental group and control groups.
A total of 951 pregnant women were included in this study, 542 participants in the experimental group and 409 participants in the control group. Descriptive statistics and birth weight of the experimental and control groups are shown in Table 1. The effect size (ES) of the birth weight differences between the experimental and control groups was -109.20 (95% CI = -432.071 to 213.663). This indicated no significant birth weight differences between the two groups since the confidence intervals crossed zero. Similarly, no significant pre-pregnancy weight differences were found between the experimental and control groups (ES = -0.776, 95% CI = -2.406 to 0.853). However, the age of the experimental group mothers was slightly higher than their counterparts (ES = 0.743, 95% CI = 0.006 to 1.480). In spite of this, the age of the experimental and control group mothers was very similar since such a small ES (i.e., 0.74) was not considered clinically important. On the other hand, when examining the birth weight of those who exercised under 30 minutes versus those who exercised between 30 and 60 minutes, both groups had a negative ES. The ES of the former was -236.047 while that of the latter was -4.143. Though the pregnant women who exercised a longer duration had a smaller absolute ES value, the overall ES (-107.838, 95% CI = -482.93 to 267.26) indicated no significant birth weight differences between the two groups because the confidence intervals crossed zero.
Since age and pre-pregnancy weight could act as confounding variables, their relationship with birth weight was examined. Liner regression analyses indicated no significant (p > .05) relationship between birth weight and the age of the experimental group (R = .04, p = .91) as well as the pre-pregnancy weight differences of the exercise and control groups (R = .05, p = .46). However, significant (p < .05) positive relationship was found between birth weight and the pre-pregnancy weight of the experimental group (R = .75, p = .04).
The purpose of this study was to use meta-analysis to examine the effects of exercise on birth weight. Only nine of the 40 articles reviewed were used for this study because the remainder did not meet the criteria for a meta-analysis. It seems that it is not a common practice in medical articles to provide standard deviations for the results (for examples, Dale, Mullinax, & Bryan, 1982; Hall & Kaufmann, 1987; Klebaboff, Shiono, & Carey, 1990; Rafla & Cook, 1999; Rafla, 2000; Rose, Haddow, Palomaki, & Knight, 1991; Schramm, Stockbauer, & Hoffman, 1996). Further, the research methodology of some of the articles is questionable, for example, no control group was used in the study (e.g., Jarrett & Spellacy, 1983). Though exercise intensity is an important variable that can affect birth weight, it was excluded from this study because there were not enough articles provide this information.
The main purpose of this study was to investigate the effect of exercise duration on birth weight. However, because pre-pregnancy weight and age of the experimental and control groups might influence the birth weight of the babies, these two variables were also examined because. The nonsignifcant pre-pregnancy weight difference and trivial ES of age between the experimental and control groups indicated that these two variables did not generate any significant impact on either group’s outcome variable (birth weight).
The ES of both exercise groups were negative, but the magnitude of those who exercised under 30 minutes was greater. This suggests that those who exercised less than 30 minutes tended to produce smaller babies than those who exercised between 30 and 60 minutes. However, in spite of this big difference in ES (i.e., -236.047 versus -4.143), no significant birth weight differences were found between the two groups. This is probably because of the small sample size in this study. If a larger sample could be included in future studies, this is a worthwhile topic for further investigation since previous researchers have suggested that pregnant women who exercised regularly delivered heavier babies than their non-exercise counterparts (Brodey, 1993; Hatch, et al., 1993; Johnson, et al., 1994). For example, Hatch et al. (1993) indicated that women expending 1000 Kcal or more a week in recreational activity throughout pregnancy had babies 310 g heavier than those who did not exercise. Further, Schramm, Stockbauer, and Hoffman (1996) demonstrated that women having very low birth weight babies (N = 782) were less likely to engage in regular and vigorous exercise during pregnancy than women with normal birth weight babies (N = 793).
In this study, no relationship was found between birth weight and the age of the experimental group. Previous researchers indicated that the risk of low birth weight babies is greatest in teenage mothers or women aged 40 or older (Pivarnik, 1998). The age of all the pregnant mothers in this study was within “normal” range (i.e., between 23 and 32 years of age) and therefore may not have generated any significant difference in birth weight. On the other hand, the significant positive relationship found between birth weight and the pre-pregnancy weight was not surprising since numerous previous research studies also found a strong positive relationship between pre-pregnancy weight and birth weight as well as between maternal weight gain and birth weight (Abrams & Laros, 1986; Abrams & Neuman, 1989; Abrams & Selvin, 1995; Brown, 1988; Frentzen, Dimperio, & Cruz, 1988; Garn, Shaw, & McCabe, 1977; Hediger, Scholl, & Salmon, 1989; Hediger, Scholl, Belsky, Ances, & Salmon, 1989; Institute of Medicine, 1990; Naeye, 1979; Nahum, Stanislaw, & Huffaker, 1998; Scholl, Hediger, Ances, Belsky, & Salmon, 1990; Thorsdottir & Birgisdottir, 1998; Wen, Goldenberg, Cutter, Hoffman, & Cliver 1990). For example, Thorsdottir and Birgisdottir (1998) found in their study that women who gained between 18 and 24 kg had babies approximately 300 g heavier than those who gained between 9 and 1: kg.
The purpose of this study was to introduce one of the many techniques that could summarize and analyze similar studies with inconsistent results. In 1991, Lokey, Tran, Wells, Myers, and Tran used “a meta-analytic review” to examine the effects of physical exercise on pregnancy outcomes. However, they used t-tests to compare the mean differences of the exercising and sedentary groups and no ES was reported. Based on a review of the literature, this is the first meta-analysis study to examine the effects of exercise on birth weight using a meta-analysis computer program and ES to determine the overall magnitude of two comparing groups. Only three variables, exercise duration, age, and pre-pregnancy weight, were examined in this study. Another potential variable that should be considered in future studies is ethnicity since black infants tended to weigh less and be twice as likely as white babies to have a low birth weight (Breslin, 1998).
On the whole, the results of this study support the notion that a significant positive relationship exists between birth weight and the pre-pregnancy weight. This conclusion is based on the results of the meta-analysis of selected publications. Of course, many other factors other than the aforesaid variables also may affect pregnancy outcomes. These factors may include maternal weight, maternal nutrition, socioeconomic status, lifestyle habits, age, poor previous pregnancy outcomes, and maternal health. It is suggested that for future medical studies, efforts should be implemented to control for potential confounding factors when manipulating independent variables and assessing dependent variables. In addition, in order to facilitate future studies using meta-analysis, the researchers recommend the following information to be included in all publications: (a) sample size, (b) experimental and control groups, (c) mean and standard deviation of the dependent variables, (e) the type of statistical analysis, and (f) the results of statistical analysis.
HEALTH EDUCATION RESPONSIBILITY AND COMPETENCY ADDRESSED
Responsibility III: Implementing Health Education Programs
Competency A: Exhibit competency in carrying out planned educational programs.
Subcompetency 5: Assess, select, and apply technologies that will contribute to program objectives.
Table 1. Descriptive Statistics of the Experimental and Control Groups.
Source Age (year) weight (kg)
Horns et al. (1996) (1) 28.4 [+ or -] 4.1 —
Lewis et al. (1988) (1) 28.4 [+ or -] 3.2 59.4 [+ or -] 8.4
Hatch et al. (1993) (1) 27.9 [+ or -] 4.6 62.2 [+ or -] 14
Botkin & Driscoll (1991) (1) 28.1 [+ or -] 5.1 —
Bell et al. (1995) (2) 31.8 [+ or -] 2.7 58.8 [+ or -] 6.9
Clapp & Capeless (1990) (2) 30.6 [+ or -] 2.5 57.7 [+ or -] 5.2
Rice & Fort (1991) (2) 23.3 [+ or -] 3.6 —
Collings et al. (1983) (2) 26.9 [+ or -] 2.8 60.3 [+ or -] 8.3
Kardel & Kase (1998) (2) 28.8 [+ or -] 2.3 59.4 [+ or -] 6.3
Source (gram) N
Horns et al. (1996) (1) 2496 [+ or -] 486 48
Lewis et al. (1988) (1) 3400 [+ or -] 700 18
Hatch et al. (1993) (1) 3554 [+ or -] 382 277
Botkin & Driscoll (1991) (1) 3664 [+ or -] 318 19
Bell et al. (1995) (2) 3353 [+ or -] 589 58
Clapp & Capeless (1990) (2) 3381 [+ or -] 322 77
Rice & Fort (1991) (2) 3500 [+ or -] 318 12
Collings et al. (1983) (2) 3596 [+ or -] 480 12
Kardel & Kase (1998) (2) 3651 [+ or -] 516 21
Source Age (year) weight (kg)
Horns et al. (1996) (1) 27.2 [+ or -] 3.8 —
Lewis et al. (1988) (1) 27.3 [+ or -] 3.4 62.8 [+ or -] 10.6
Hatch et al. (1993) (1) 27.1 [+ or -] 4.4 62.5 [+ or -] 11.7
Botkin & Driscoll (1991) (1) 27.2 [+ or -] 5.5 —
Bell et al. (1995) (2) 31.6 [+ or -] 4.7 59.1 [+ or -] 7.6
Clapp & Capeless (1990) (2) 30.1 [+ or -] 3.3 58.1 [+ or -] 5.9
Rice & Fort (1991) (2) 26.2 [+ or -] 5.1 —
Collings et al. (1983) (2) 28.0 [+ or -] 3.7 64.4 [+ or -] 8.4
Kardel & Kase (1998) (2) 26.7 [+ or -] 1.7 63.0 [+ or -] 8.9
Source (gram) N
Horns et al. (1996) (1) 3467 [+ or -] 434 53
Lewis et al. (1988) (1) 3700 [+ or -] 500 10
Hatch et al. (1993) (1) 3389 [+ or -] 488 185
Botkin & Driscoll (1991) (1) 3523 [+ or -] 351 25
Bell et al. (1995) (2) 3364 [+ or -] 412 41
Clapp & Capeless (1990) (2) 3691 [+ or -] 348 55
Rice & Fort (1991) (2) 3455 [+ or -] 450 11
Collings et al. (1983) (2) 3354 [+ or -] 415 8
Kardel & Kase (1998) (2) 3591 [+ or -] 532 21
Data reported as mean [+ or -] standard deviation
(1) Group 1: Exercised under 30 minutes
(2) Group 2: Exercised 30 to 60 minutes
Abrams, B. E, & Laros, R. K. (1986). Prepregnancy weight, weight gain, and birth weight. American Journal of Obstetrics and Gynecology 154, 503-509.
Abrams, B., & Neuman, V. (1989). Maternal weight gain and preterm delivery. Obstetrics and Gynecology, 74, 377-383.
Abrams, B., & Selvin, S. (1995). Maternal weight gain pattern and birth weight. Obstetrics and Gynecology, 86, 163-169.
Bangert-Drowns, R. L. (1988). The effects of school-based substance abuse education: A meta-analysis. Journal of Drug Education, 18(3), 243-265.
* Bell, R. J., Palma, S. M., & Lumley, J. M. (1995). The effect of vigorous exercise during pregnancy on birth-weight. Australian and New Zealand Journal of Obstetrics and Gynecology, 35(1), 46-51.
Bell, R., & O’Neill, M. (1994). Exercise and pregnancy: A review. Birth, 21(2), 85-95.
* Botkin, C., & Driscoll, C. E. (1991). Maternal aerobic exercise: Newborn effects. Family Practice Research Journal 11, 387-393.
Breslin, M. (1998). Women’s birth weight and intrauterine nutrition may have an effect on their infant’s birth weight. Family Planning Perspectives, 30, 148-149.
Brodey, D. (1993, November). Building bigger babies. American Health, 88.
Brown, J. E. (1988). Weight gain during pregnancy: What is “optimal?” Clinical Nutrition, 7, 181-190.
Brown, J. E., & Kahn, E. S. (1997). Maternal nutrition and the outcome of pregnancy: A renaissance in research. Clinics in Perinatology, 24(2), 433-449.
Clapp, J. F., III. (1996). The effect of continuing regular endurance exercise on the physiologic adaptations to pregnancy and pregnancy outcome. American Journal of Sports Medicine, 24(6), S28-S29.
* Clapp, J. F., III., & Capeless, E. L. (1990). Neonatal morphometrics after endurance exercise during pregnancy. American Journal of Obstetrics and Gynecology, 163(6 pt 1), 1805-1811.
Clapp, J. F., III., & Dickstein, S. (1984). Endurance exercise and pregnancy outcome. Medicine and Science in Sports and Exercise, 16, 556-562.
Cnattingius, S., Bergstrom, R., Lipworth, L., & Kramer, M. S. (1998). Prepregnancy weight and the risk of adverse pregnancy outcomes. New England Journal of Medicine, 338, 147-152.
* Collings, C. A., Curet, L. B., & Mullin, J. P. (1983). Maternal and fetal responses to a maternal aerobic exercise program. American Journal of Obstetrics and Gynecology 145, 702-707.
Dale, E., Mullinax, K. M., & Bryan, D. H. (1982). Exercise during pregnancy: Effects on the fetus. Canadian Journal of Applied Sport Sciences, 7(2), 98-103.
Edwards, L. E., Hellerstedt, W. L., Alton, I. R., Story, M., & Himes, J. H. (1996). Pregnancy complications and birth outcomes in obese and normal-weight women: Effects of gestational weight change. Obstetrics and Gynecology, 87, 389-457.
Frentzen, B., Dimperio, D., & Cruz, A. (1988). Maternal weight gain: Effect on infant birth weight among over weight and average weight low-income women. American Journal of Obstetrics and Gynecology 159, 11141117.
Garn, S. M., Shaw, H. A., & McCabe, K. D. (1977). Effects of socioeconomic status and race on weight defined and gestational prematurity in the United States. In D. M. Reed, & E J. Stanley (Eds.), The epidemiology of prematurity (pp. 127-143). Baltimore: Urban and Schwarzenberg.
Glass, G. V. (1977). Integrating findings: The meta-analysis of research. Review of Research in Education, 6, 351-379.
Gorski, J. (1985). Exercise during pregnancy: Maternal and fetal responses. A brief review. Medicine and Science in Sports and Exercise, 17, 407-416.
Gortzak-Uzan, L., Hallak, M., Press, E, Katz, M., & Shoham-Vardi, I. (2001). Teenage pregnancy: risk factors for adverse perinatal outcome. Journal of Maternal Fetal Medicine, 10, 393-397.
Hall, D. C., & Kaufmann, D. A. (1987). Effects of aerobic and strength conditioning on pregnancy outcomes. American Journal of Obstetrics and Gynecology, 157, 1199-1203.
* Hatch, M. C., Shu, X. O., McLean, D. E., Levin, B., Begg, M., Reuss, L., & Susser, M. (1993). Maternal exercise during pregnancy, physical fitness, and fetal growth. American Journal of Epidemiology, 137, 1105-1114.
Hedges, L. V., & Olkin, I. (1985). Statistical methods for meta-analysis. Orlando, FL: Academic Press.
Hediger, M., Scholl, T., & Salmon, R. (1989). Early weight gain in pregnant adolescents and fetal outcome. American Journal of Human Biology, 1,665-672.
Hediger, M., Scholl, T., Belsky, D., Ances, I., & Salmon, R. (1989). Patterns of weight gain in adolescent pregnancy: Effects on birth weight and preterm delivery. Obstetrics and Gynecology, 74, 6-12.
* Horns, P. N., Ratcliffe, L. P., Leggett, J. C., & Swanson, M. S. (1996). Pregnancy outcomes among active and sedentary primiparous women. Journal of Obstetric, Gynecologic and Neonatal Nursing, 25, 49-54.
Institute of Medicine. (1990). Committee on Nutritional Status During Pregnancy and Lactation, Food and Nutrition Board: Nutrition during pregnancy part 1 (II), nutrition supplements. Washington, DC: National Academy Press.
International Journal of Gynaecology and Obstetrics, 73(2), 101-107.
Jarrett, J. C., II., & Spellacy, W. N. (1983). Jogging during pregnancy: An improved outcome? Obstetrics and Gynecology 61,705-709.
Johnson, A. A., Knight, E. M., Edwards, C. H., Oyemade, U. J., Cole, O. J., Westney, O. E., Westney; L. S., Laryea, H., & Jones, S. (1994). Selected lifestyle practices in urban African American women-relationships to pregnancy outcome, dietary intakes and anthropometric measurements. Journal of Nutrition, 124(supp. 6), 963S-972S.
Jones, O., Rodar, D., & Chan, A. (1992). The association of socio-economic status in metropolitan Adelaide with maternal demographic and obstetric characteristics and pregnancy outcome. European Journal of Epidemiology 8, 708-714.
Kallen, K. (2001). The impact of maternal smoking during pregnancy on delivery outcome. European Journal of Public Health, 11,329-333.
* Kardel, K. R., & Kase, T. (1998). Training in pregnant women: Effects on fetal development and birth. American Journal of Obstetrics and Gynecology 178, 280-286.
Klebanoff, M. A., Shiono, P. H., & Carey, J. C. (1990). The effect of physical activity during pregnancy on preterm delivery and birth weight. American Journal of Obstetrics and Gynecology, 163, 1450-1456.
Korea, G., Pastuszak, A., & Ito, S. (1998). Drugs in pregnancy. New England Journal of Medicine, 338, 1128-1137.
Kumari, A. S. (2001). Pregnancy outcome in women with morbid obesity.
Largo, R. H., Pfister, D., Molinari, L., Kundu, S., Lipp, A., & Duc, G. (1989). Significance of prenatal, perinatal and postnatal factors in the development of AGA preterm infants at five to seven years. Developmental Medicine and Child Neurology, 31,440-456.
* Lewis, R. D., Yates, C. Y., & Driskell, J. A. (1988). Riboflavin and thiamin status and birth outcome as a function of maternal aerobic exercise. American Journal of Clinical Nutrition, 48, 110-116.
Lokey, E. A., Tran, Z. V., Wells, C. L., Myers, B. C., & Tran, A. C. (1991). Effects of physical exercise on pregnancy outcomes: A meta-analytic review. Medicine and Science in Sports and Exercise, 23, 1234-1239.
Lopez, N. J., Smith, P. C., & Gutierrez, J. (2002). Higher risk of preterm birth and low birth weight in women with periodontal disease. Journal of Dental Research, 81(1), 58-63.
Marlow, N., Roberts, B. L., & Cook, R. (1989). Motor skills in extremely low birthweight children at the age of 6 years. Archives of Disease in Childhood, 64, 839-847.
Matsuno, A. Y., Esrey, K. L., Perrault, H., & Koski, K. G. (1999). Low intensity exercise and varying proportions of dietary glucose and fat modify milk and mammary gland compositions and pup growth. Journal of Nutrition, 129, 1167-1175.
McCormick, M. C., Gortmaker, S. L., & Sobol, A. M. (1990). Very low birth weight children: Behavior problems and school difficulty in a national sample. Journal of Pediatrics, 117, 687-693.
Meyer, R. E., Buescher, P. A., & Surles, K. B. (1999). Multiple deliveries and effects on birth outcomes. Matern Child Health, 3, 233-240.
Naeye, R. L. (1979). Weight gain and the outcome of pregnancy. American Journal of Obstetrics and Gynecology 135, 3-9.
Nahum, G. G., Stanislaw, H., & Huffaker, B. J. (1998). Accurate prediction of term birth weight from prospectively measurable maternal characteristics. Sonography and Interventional Radiology 5(4), 193-194,
Ogunyemi, D., Hullett, S., Leeper, J., & Risk, A. (1998). Prepregnancy body mass index, weight gain during pregnancy, and perinatal outcome in a rural black population. Journal of Maternal Fetal Medicine, 7, 190-193.
Ornstein, M., Ohlsson, A., Edmonds, J., & Asztalos, E. (1991). Neonatal follow-up of very low birthweight/ extremely low birthweight infants to school age: A critical overview. Acta Paediatrica Scandinavica, 80, 741-748.
Otterblad-Olausson, P. M., Cnattingius, S., & Goldenberg, R. L. (1997). Determinants of poor pregnancy outcomes among teenagers in Sweden. Obstetrics and Gynecology, 89, 451-457.
Pharoah, P., Stevenson, C. J., Cooke, R., & Stevenson, 1L C. (1994). Clinical and subclinical deficits at 8 years in a geographically defined cohort of low birthweight infants. Archives of Disease in Childhood, 70, 264-270.
Pivarnik, J. M. (1998). Potential effects of maternal physical activity on birth weight: Brief review. Medicine and Science in Sports and Exercise, 30, 400-406.
Pivarnik, J. M., Mauer, M. B., Ayres, N. A., Kirshon, B., Dildy, G.A., & Cotton, D. B. (1994). Effects of chronic exercise on blood volume expansion and hematologic indices during pregnancy. Obstetrics and Gynecology 83, 265-269.
Rafla, N. M. (2000). The effect of maternal exercise on umbilical artery blood flow in pregnancy-induced hypertension. Journal of Obstetrics and Gynecology, 20, 19-23.
Rafla, N. M., & Cook, J. R. (1999). The effect of maternal exercise on fetal heart rate. Journal of Obstetrics and Gynecology, 19, 381-384.
* Rice, P. L., & Fort, I. L. (1991). The relationship of maternal exercise on labor, delivery and health of the newborn. Journal of Sports Medicine and Physical Fitness, 31, 95-99.
Rose, N. C., Haddow, J. E., Palomaki, G. E., & Knight, G.J. (1991). Self-rated physical activity level during the second trimester and pregnancy outcome. Journal of Obstetrics and Gynecology, 78, 1078-1080.
Rosenberg, M. S., Adams, D. C., & Gurevitch, J. (2000). Meta Win 2.0. Sunderland, MA: Sinauer.
Scholl, T. O., & Johnson, W. G. (2000). Folic acid: Influence on the outcome of pregnancy. American Journal of Clinical Nutrition, 71(5S), 1295S-1303S.
Scholl, T. O., Hediger, M., Ances, I., Belsky, D., & Salmon, R. (1990). Weight gain during pregnancy in adolescence: Predictive ability of early weight gain. Obstetrics and Gynecology 75, 898-919.
Schramm, W. F., Stockbauer, J. W., & Hoffman, H, J. (1996). Exercise, employment, other daily activities and adverse pregnancy outcomes. American Journal of Epidemiology, 143(3), 211-218.
Seoud, M., Nassar, A. H., Usta, I. M., Melhem, Z., Kazma, A., & Khalil, A. M. (2002). Impact of advanced maternal age on pregnancy outcome. American Journal of Perinatology, 19(1), 1-8.
Sibai, B. M. (1996). Treatment of hypertension in pregnant women. New England Journal of Medicine, 335, 257-265.
Sommerfeldt, K., Ellersten, B., & Markestad, T. (1995). Parental factors in cognitive outcome of non-handicapped low birthweight infants. Archives of Disease in Childhood, 73, F135-F142.
Sommerfeldt, K., Ellersten, B., & Markestad, T. (1996). Low birthweight and neuromotor development: A population based, controlled study. Acta Paediatrica, 85, 604-610.
Sommerfeldt, K., Troland, K., Ellersten, B., & Markestad, T. (1996). Behavioral problems in low birthweight preschoolers. Developmental Medicine and Child Neurology, 38, 927-940.
Spatling, L., Fallenstein, F., Huch, A., Huch, R., & Rooth, G. (1992). The variability of cardiopulmonary adaptation to pregnancy at rest and during exercise. British Journal of Obstetrics and Gynecology, 99(Supp. 8), 1-40.
Sternfeld, B. (1997). Physical activity and pregnancy outcome: Review and recommendations. Sports Medicine, 23, 33-47.
Sternfeld, B., Quesenberry, C. P., Jr., Eskenazi, B., & Newman, L. A. (1995). Exercise during pregnancy and pregnancy outcome. Medicine and Science in Sports and Exercise, 27, 634-640.
Story, M., & Alton, I. (1995). Nutrition issues and adolescent pregnancy. Nutrition Today, 30(4), 142-151.
Szatmari, P., Saigal, S., Rosenbaum, P., Campbell, D., & King, S. (1990). Psychiatric disorders at five years among children with birthweights less than 1000 g: A regional perspective. Developmental Medicine and Child Neurology, 32, 954-962.
Thorsdottir, I., & Birgisdottir, B. E. (1998). Different weight gain in women of normal weight before pregnancy: Postpartum weight and birthweight. Obstetrics and Gynecology, 92, 377-380.
Wen, S., Goldenberg, R. L., Cutter, G. R., Hoffman, H. J., & Cliver, S. P. (1990). Intrauterine growth retardation and preterm delivery: Risk factors in an indigent population. American Journal of Obstetrics and Gynecology, 162, 213-218.
Xiong, X., Demianczuk, N. N., Saundersm, L. D., Wang, F., & Fraser, W. D. (2002). Impact of preeclampsia and gestational hypertension on birth weight by gestational age. American Journal of Epidemiology 155, 203-209.
Zhu, B., Haines, K. M., Le, T., McGrath-Miller, K., & Boulton, M. L. (2001). Effect of the interval between pregnancies on perinatal outcome among white and black women. American Journal of Obstetrics and Gynecology, 185, 1403-1410.
References with * were used for the meta-analysis.
Eddie T. C. Lam, Ph.D., Jill M. Black, Ph.D., CHES, Kathleen D. Little, Ph.D., Judith Ausherman, Ed.D., CHES and Codruta Rafiroiu, M.D., Ph.D. are in the Department of Health, Physical Education, Recreation, & Dance at Cleveland State University. Address all correspondence to Eddie T. C. Lam, Ph.D., Department of Health, Physical Education, Recreation, & Dance, Cleveland State University, 2121 Euclid Avenue, PE 218, Cleveland, OH 44115-2214; PHONE: 216.687.5051; FAX: 216.687.5410; E-MAIL: firstname.lastname@example.org.
COPYRIGHT 2002 University of Alabama, Department of Health Sciences
COPYRIGHT 2003 Gale Group