Objective
The purpose of this study was to examine the Institute of Medicine (IOM) guidelines for gestational weight gain in adolescents.
Study Design
We studied a retrospective cohort using the Missouri Birth Certificate Registry and included subjects who were primiparous, who had singleton gestations, who were <20 years old, and who delivered at 24-44 weeks gestation. The exposure was defined as weight gain less than, within, or greater than IOM recommendations. Outcomes that were examined were small-for-gestational-age (SGA) infants, large-for-gestational age (LGA) infants, preterm delivery, infant death, preeclampsia, cesarean delivery, and operative vaginal delivery. The analysis was stratified by body mass index category.
Results
In any body mass index category, inadequate weight gain was associated with increased odds of SGA infants, preterm delivery, and infant death. When subjects gained more than the IOM recommendations, the number of SGA infants decreased, with slight increases in the number of LGA infants, preeclampsia, and cesarean delivery.
Conclusion
Adolescents should be counseled regarding adequate weight gain in pregnancy. Further research is necessary to determine whether the IOM recommendations recommend enough weight gain in adolescents to optimize pregnancy outcomes.
Adolescent pregnancy is complicated not only by its unique social aspects but also by the increased risk of complications, which include preeclampsia, preterm birth, and low infant birthweight. In 2006, the rate of low birthweight (<2500 g) in infants of teenagers was as high as 13.4%, compared with 8.3% for the entire population. Although the reason for the increased rate of low birthweight infants among adolescent mothers is unclear, it is well-known that maternal weight gain is correlated to infant birthweight, either because gestational weight gain is associated causally with fetal growth or because the same determinants of gestational weight gain (diet and exercise) also impact fetal growth. Whether the effect of gestational weight gain is causal or merely associative, this association may provide a pathway to decrease the number of low birthweight infants in this population.
On the other hand, excessive gestational weight gain leads to postpartum weight retention and obesity, which is a fact that is particularly important in adolescents who are likely to have subsequent pregnancies. Additionally, excessive weight gain is linked with a higher rate of LGA infants, fetal distress, gestational diabetes mellitus, and preeclampsia.
The Institute of Medicine (IOM) recommendations on gestational weight gain focus on adults without specific recommendations for adolescents. In fact, the use of adult body mass index (BMI) categories misclassifies adolescents into a lighter BMI group, which would result in higher weight gain recommendations than if adolescent-specific BMI guidelines are used. For example, a 16-year-old girl with a BMI of 18 would be underweight according to IOM classifications, and the recommendations for her weight gain would be 28-45 pounds. However, according to age-specific BMI categories, she would be normal weight, which would result in weight gain recommendations of 25-35 pounds. The IOM justifies this misclassification because “… young teens often need to gain more to improve birthweight outcomes.” However, whether the misclassification of adolescents results in recommendations for enough gestational weight gain to maximize pregnancy outcome or whether it results in excessive gestational weight gain remains unclear.
Therefore, we sought to examine the IOM recommendations for gestational weight gain in adolescents by investigating the relationship of weight gain less than, within, or greater than the IOM recommendations with pregnancy outcomes and infant birthweight.
Materials and Methods
This was a population-based, retrospective cohort study that was based on Missouri linked birth, fetal, and infant death certificate data from 1989-2005. The database includes parental demographic information, medical and obstetrical characteristics and complications, and neonatal status at birth for each birth that occurred in the state. The study was exempt from institutional board review because all of the information was deidentified.
Our study sample consisted of primiparous women who were <20 years old who delivered singleton pregnancies from 24-44 weeks of gestation in Missouri between January 1, 1989, and December 31, 2005. We elected to include only primiparous patients to remove confounding factors of the previous pregnancy, such as previous cesarean delivery. Gestational age from the present study was based on the birth certificate variable “clinical estimate of gestation” because it more accurately reflects gestational age at delivery than length of pregnancy that was calculated by the last menstrual period. Pregnancies that are complicated by major fetal anomalies or breech presentation were excluded because this would impact the outcomes of interest. Multifetal gestations were excluded because the IOM recommendations are specifically for singleton gestations, and multifetal gestations are anticipated to require higher weight gains.
The exposure of interest for this study was gestational weight gain, which is a self-reported measure that was obtained from the birth certificate. The study sample was divided into 3 exposure groups that were based on the IOM recommendations for gestational weight gain according to each BMI weight category. The 3 groups included those who gained below recommendations, within recommendations, and above recommendations for gestational weight gain. BMI, calculated as weight per height (kilograms per square meter), was categorized according to the IOM recommendations: underweight (BMI, <18.5 kg/m 2 ), normal weight (BMI, 18.5-24.9 kg/m 2 ), overweight (BMI, 25-29.9 kg/m 2 ), and obese (BMI, ≥30 kg/m 2 ). Because gestational weight gain is in part dependent on how long a subject remains pregnant, expected gestational weight gain for preterm patients was calculated based on IOM recommendations with the use of the recommended first-trimester weight gain (1.1-4.4 kg) and the estimated weight gain per week based on BMI category.
Outcomes of interest for the present study included small-for-gestational-age (SGA) infant, large-for-gestational-age (LGA) infant, preterm delivery, infant death, preeclampsia, and cesarean delivery. SGA and LGA were measured as birthweight <10th percentile and >90th percentile, respectively, for gestational age and race/ethnicity; the United States population served as the reference for fetal growth. Preterm delivery was defined as delivery at <37 weeks’ gestation. Infant deaths were those that occurred within the first year of life. Because of the small number of subjects with eclampsia, all adolescents for whom the condition “pregnancy-induced hypertension (preeclampsia)” or “eclampsia” was checked on the Missouri birth certificate were considered to have had preeclampsia. For the cesarean delivery outcome, 2 binary indicators were constructed: all cesarean deliveries that referred to primary elective and emergency cesarean delivery as indicated on the birth certificate and unplanned cesarean delivery for primary emergency cesarean deliveries.
The 1990 IOM recommendations for gestational weight gain suggested that adolescents should gain in the upper one-half of the recommendations for each BMI category; the 2009 recommendations do not make this suggestion. As a secondary analysis, we examined the incidence of outcomes in those girls who gained in the bottom one-half vs the top one-half of the IOM recommendations.
Differences in sample characteristics by BMI categories were assessed with the Pearson chi-square test (χ 2 ) for categoric variables and t test for continuous variables. For each BMI weight category, we examined the relationship of weight gain less than, within, or greater than the IOM recommendations with pregnancy outcomes and infant birthweight. Odds ratios (ORs) and the 95% confidence interval (CI) were estimated with binary logistic regression.
Factors that may be associated with gestational weight gain and outcomes of interest were evaluated as potential confounders. Data for the following maternal demographic and lifestyle variables were obtained from the birth certificate: maternal age, race (white or black), smoking or alcohol use during pregnancy (yes or no), Medicaid use (yes or no), prepregnancy BMI, Kotelchuck prenatal care index (a measure of the adequacy of prenatal care as determined by the month in which prenatal care began and the percentage of visits attended), and a binary composite maternal medical risk factor (includes chronic hypertension, diabetes mellitus, and renal disease). For easier parameter estimate interpretation, maternal age was mean centered. All tests were 2-tailed; a probability value of < .05 was considered significant. All statistical analyses were performed with STATA software (version 10.0; STATA Corporation, College Station, TX).
Results
Of 979,849 singleton pregnancies in the Missouri birth certificate registry during the study period, 116,465 were to adolescents ( Figure ). After exclusion of multiparous subjects, congenital fetal anomalies, and breech presentation, the cohort consisted of 76,682 subjects. In our study sample, 10,291 adolescents (13.42%) were underweight; 48,167 adolescents (62.81%) were normal weight; 11,945 adolescents (15.58%) were overweight, and 6279 adolescents (8.19%) were obese ( Table 1 ). Most of the adolescents in our study were 17-19 years old; the average age was 17 years. Overweight and obese adolescents were more likely to be black and Medicaid recipients and to have chronic hypertension and diabetes mellitus. Underweight and normal-weight adolescents were more likely to be white and to smoke during pregnancy.
| Variable | Body mass index | P value | |||
|---|---|---|---|---|---|
| Underweight: <18.5 kg/m 2 (n = 10,291) | Normal weight: 18.5-24.9 kg/m 2 (n = 48,167) | Overweight: 25.0-29.9 kg/m 2 (n = 11,945) | Obese: ≥30 kg/m 2 (n = 6279) | ||
| Age, y a | 17.49 ± 1.30 | 17.55 ± 1.31 | 17.73 ± 1.28 | 17.96 ± 1.16 | < .01 |
| White, n (%) | 8565 (83.23) | 36,012 (74.76) | 8254 (69.10) | 4209 (67.03) | < .01 |
| Black, n (%) | 1726 (16.77) | 12,155 (25.24) | 3691 (30.90) | 2070 (32.97) | |
| Medicaid, n (%) | 7756 (75.51) | 35,556 (73.95) | 9227 (77.38) | 5042 (80.43) | < .01 |
| Smoking, n (%) | 3263 (31.74) | 11,701 (24.32) | 2697 (22.62) | 1460 (23.30) | < .01 |
| Alcohol use, n (%) | 361 (0.75) | 73 (0.71) | 77 (0.65) | 46 (0.73) | .68 |
| Chronic hypertension, n (%) | 84 (0.17) | 8 (0.08) | 49 (0.41) | 67 (1.07) | < .01 |
| Diabetes mellitus, n (%) | 51 (0.50) | 325 (0.68) | 145 (1.21) | 153 (2.44) | < .01 |
| Weight gain, n (%) | < .01 | ||||
| Less than Institute of Medicine guideline | 2808 (27.2) | 10,249 (21.3) | 1050 (8.8) | 688 (11.0) | |
| Within Institute of Medicine guideline | 4404 (42.8) | 16,296 (33.8) | 2411 (20.2) | 1090 (17.4) | |
| More than Institute of Medicine guideline | 3079 (29.9) | 21,621 (44.9) | 8478 (71.0) | 4501 (71.7) | |
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
