Objective
We aimed to examine whether women who adhered to Institute of Medicine (IOM) guidelines for gestational weight gain (GWG) had improved perinatal outcomes.
Study Design
This is a population-based retrospective cohort study of nulliparous women with term singleton vertex births in the United States from 2011 through 2012. Women with medical or obstetric complications were excluded. Prepregnancy body mass index was calculated using reported weight and height. Women were categorized into 4 groups based on GWG and prepregnancy body mass index: (1) weight gain less than, (2) weight gain within, (3) weight gain 1-19 lb in excess of, and (4) weight gain ≥20 lb in excess of the IOM guidelines. The χ 2 test and multivariable logistic regression analysis were used for statistical comparisons.
Results
Compared to women who had GWG within the IOM guidelines, women with excessive weight gain, particularly ≥20 lb, were more likely to have adverse maternal outcomes (preeclampsia: adjusted odds ratio [aOR], 2.78; 95% confidence interval [CI], 2.82–2.93; eclampsia: aOR, 2.51; 95% CI, 2.27–2.78; cesarean: aOR, 2.1; 95% CI, 2.14–2.19), blood transfusion (aOR, 1.22; 95% CI, 1.11–1.33), and neonatal outcomes (5-minute Apgar <4: aOR, 1.22; 95% CI, 1.14–1.31; ventilation use >6 hours: aOR, 1.24; 95% CI, 1.15–1.33; seizure: aOR, 1.53; 95% CI, 1.24–1.89). Women who gained less than IOM guidelines had lower risks of hypertensive disorders of pregnancy and obstetric interventions but were more likely to have small-for-gestational-age neonates (aOR, 1.55; 95% CI, 1.52–1.59).
Conclusion
Women whose GWG is in excess of IOM guidelines have higher risk of adverse maternal and neonatal outcomes, particularly in women with ≥20 lb excess weight gain above guidelines while women who had weight gain below the IOM guidelines were less likely to have maternal morbidity but had higher odds of small for gestational age.
In 2009, the Institute of Medicine (IOM) put forth new guidelines regarding how much weight women should gain during pregnancy. The impetus for the update was partly due to the increasing availability of data on the effect of gestational weight gain (GWG) on perinatal outcomes as well as the changing obstetric population over time since its last recommendation in 1990. In particular, the 1990 guidelines did not give an upper limit for weight gain in obese patients whereas the revised 2009 guidelines gave a specific recommended range for obese women. Compared to decades prior, women in the United States today are more likely to delay childbearing, have greater access to assisted reproductive technology, have multifetal gestations, have greater racial/ethnic diversity, and be overweight or obese. All of these factors contribute to the fact that up to 70% of pregnant women gain weight in excess of current IOM guidelines.
Previous studies have shown that increasing GWG is associated with higher risk of gestational hypertension, preeclampsia, and cesarean delivery. Additionally, some studies have shown that increased GWG is associated with adverse neonatal outcomes such as fetal macrosomia, low Apgar score, hypoglycemia, admission to the neonatal intensive care unit (NICU), and prolonged hospital stay. There are additional studies associating higher GWG and increased risks of childhood obesity.
Since the release of the IOM guidelines on GWG in 2009, data remain scarce regarding whether adherence to the guidelines is associated with improved perinatal outcomes. Moreover, obesity and excessive GWG continue to be growing public health problems, yet it remains unclear whether there are increasing odds of adverse outcomes with increasing GWG above IOM guidelines. Thus, we designed a population-based, retrospective cohort study to examine GWG classified by the IOM guidelines and associated perinatal outcomes. Our hypothesis was that women who had GWG below or above the IOM guidelines were at higher risk of maternal and neonatal morbidity compared to women whose weight gain was in accordance with the IOM guidelines, particularly in the obese women.
Materials and Methods
This is a population-based retrospective cohort study of low-risk nulliparous women with term singleton vertex live births in the United States from 2011 through 2012 using the Vital Statistics Natality birth certificate registry provided and maintained by the Centers for Disease Control and Prevention National Center for Health Statistics. This data set included births to US and non-US residents that occurred in the 50 United States, and the District of Columbia. The 2011 through 2012 birth data were compiled using either the 2003 Revision or the 1989 Revision of US Standard Certificate of Live Birth. Thirty-six states and the District of Columbia had implemented the revised birth certificate in 2011: California, Colorado, Delaware, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Michigan, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Washington, Wisconsin, and Wyoming. These states represent 83% of live births to US citizens in 2011. In 2012, 2 additional states, Massachusetts and Minnesota, also compiled birth data using the 2003 Revision of US Standard Certificate of Live Birth; these 38 states as well as the District of Columbia represent 86.3% of births to US citizens in 2012. Since information on prepregnancy weight and height was collected in the 2003 Revision of US Standard Certificate of Live Birth but not in the 1989 Revision, women who gave birth in states using the 1989 Revision in 2011 or 2012 were excluded from analysis. Additionally, we excluded women with medical or obstetric conditions (prepregnancy diabetes mellitus, chronic hypertension, prior preterm birth, and history of poor pregnancy outcome) as well as women who had missing information regarding prepregnancy weight, height, or weight gain in pregnancy.
Collection of information on maternal height and prepregnancy weight was by direct self-report via the Mother’s Worksheet for the Child’s Birth Certificate (available at http://www.cdc.gov/nchs/data/dvs/momswkstf_improv.pdf ). More specifically, questions regarding height and prepregnancy weight were: “What is your height?” and “What was your prepregnancy weight, that is, your weight immediately before you become pregnant with this child?” Information on mother’s weight at delivery was collected directly from the medical record. The acceptable range of maternal weight values is 50-400 lb; values out of this range were edited to “not stated” in the natality data and treated as missing, thus not included for the analysis. GWG in pregnancy was calculated by subtracting each individual mother’s prepregnancy weight from her weight at delivery. Prepregnancy body mass index (BMI) was calculated using the below formula:
( [ prepregnancy weight {lb} ] / [ height {in} ] 2 ) × 703
Women were categorized into 4 groups based on prepregnancy BMI and GWG relative to the IOM guidelines ( Table 1 ): (1) weight gain below, (2) weight gain within, (3) weight gain 1-19 lb above, and (4) weight gain ≥20 lb above the IOM guidelines.
| Variable | Prepregnancy BMI | Total weight gain range, lb | Rates of weight gain in second and third trimester, mean (range), lb/wk |
|---|---|---|---|
| Underweight | <18.5 | 28–40 | 1 (1–1.3) |
| Normal weight | 18.5–24.9 | 25–35 | 1 (0.8–1) |
| Overweight | 25–29.9 | 15–25 | 0.6 (0.5–0.7) |
| Obese (all classes) | ≥30 | 11–20 | 0.5 (0.4–0.6) |
Perinatal outcomes were compared between the 4 groups of women who had GWG below, within, 1-19 lb above, or ≥20 lb above the IOM guidelines. Maternal outcomes examined included gestational diabetes mellitus (GDM), gestational hypertension/preeclampsia, eclampsia, induction of labor, cesarean delivery, chorioamnionitis, antibiotics use, postpartum hemorrhage requiring blood transfusion, and intensive care unit (ICU) admission. Neonatal outcomes examined were 5-minute Apgar <4, mechanical ventilation use >6 hours, neonatal seizures, NICU admission, birth trauma, antibiotics use, neonatal transfer to higher-level nursery, large for gestational age (LGA) (>97th percentile), and small for gestational age (SGA) (<3rd percentile). The χ 2 test was used to compare dichotomous outcomes and multivariable logistic regression analysis was used to control for potential confounding. Women whose gestational weight fell within the IOM guidelines were designated as the referent. Covariates included in the multivariable logistic regression model included: maternal age, race/ethnicity, education, marital status, and medical insurance/payment source. A P value < .05 and 95% confidence intervals (CIs) were used to designate statistical significance. As the Natality data are publically available and de-identified of patient privacy information, this study was deemed exempt from review by the institutional review board at the Oregon Health & Science University.
Results
Of the 2,102,642 women who met study criteria, 17.3% had weight gain less than, 30.3% had weight gain within, 39.3% gained 1-19 lb above, and 13.2% gained ≥20 lb above the IOM guidelines. In this cohort, women age ≤19 years at time of delivery were more likely to gain below the IOM guidelines (21.2%) compared to other age groups (16.3-18.1%, P < .001) ( Table 2 ). Characteristics associated with GWG in concordance with the IOM guidelines included age ≥35 years, Asian race/ethnicity, ≥16 years of education, being married, and having private health insurance as well as BMI within normal range (18.5-24.9 kg/m 2 ; P < .001) ( Table 2 ). Characteristics associated with GWG above IOM guidelines included age 20-34 years, ≤15 years of education, being unmarried, and prepregnancy BMI within overweight and obese range (≥25 kg/m 2 ; P < .001 for all) ( Table 2 ). The proportion of women who gained below, within, and above the IOM guidelines were relatively stable during the study period ( Table 2 ).
| Characteristic | Below IOM guidelines | Within IOM guidelines | 1–19 lb above IOM guidelines | ≥20 lb above IOM guidelines | P value |
|---|---|---|---|---|---|
| Age, y | |||||
| <19 (n = 355,594) | 21.2% | 28.3% | 36.4% | 14.1% | |
| 20–34 (n = 1,590,329) | 16.3% | 30.3% | 40.1% | 13.3% | < .001 |
| ≥35 (n = 159,719) | 18.1% | 34.2% | 37.8% | 9.9% | |
| Race/ethnicity | |||||
| Caucasian (n = 1,275,772) | 15.1% | 29.6% | 41.0% | 14.3% | |
| African American (n = 281,397) | 21.4% | 27.1% | 36.8% | 14.7% | |
| Latina (n = 348,030) | 19.8% | 31.5% | 37.8% | 10.9% | < .001 |
| Asian (n = 154,091) | 22.7% | 39.5% | 32.8% | 5.0% | |
| Other (n = 43,352) | 16.5% | 26.7% | 39.9% | 16.8% | |
| Education, y | |||||
| 0–11 (n = 298,365) | 23.0% | 28.6% | 35.0% | 13.4% | |
| 12 (n = 499,297) | 18.2% | 28.0% | 38.7% | 15.1% | < .001 |
| 13–15 (n = 452,344) | 16.0% | 27.7% | 40.8% | 15.5% | |
| ≥16 (n = 833,601) | 15.3% | 33.6% | 40.4% | 10.7% | |
| Marital status | |||||
| Not married (n = 983,187) | 18.6% | 27.8% | 38.3% | 15.3% | < .001 |
| Married (n = 1,119,455) | 16.1% | 32.5% | 40.1% | 11.3% | |
| Insurance payer type | |||||
| Medicaid (n = 842,514) | 19.1% | 28.1% | 38.0% | 14.8% | |
| Private (n = 1,133,311) | 15.8% | 32.0% | 40.3% | 11.9% | < .001 |
| Self-pay (n = 55,663) | 16.9% | 29.1% | 39.9% | 14.1% | |
| Other (n = 71,154) | 19.1% | 29.9% | 38.1% | 12.9% | |
| BMI weight category, kg/m 2 | |||||
| <18.5 (n = 103,939) | 28.3% | 44.6% | 22.8% | 4.3% | |
| 18.5–24.9 (n = 1,116,536) | 20.0% | 36.9% | 35.9% | 7.2% | < .001 |
| 25.0–29.9 (n = 489,996) | 9.8% | 20.7% | 46.8% | 22.7% | |
| ≥30.0 (n = 392,171) | 16.1% | 19.7% | 43.7% | 20.5% | |
| Birth year | |||||
| 2011 (n = 1,039,921) | 17.2% | 30.2% | 39.4% | 13.2% | < .001 |
| 2012 (n = 1,062,721) | 17.4% | 30.3% | 39.1% | 13.1% |
Compared to women who had weight gain within the IOM guidelines, the women who gained below the IOM guidelines were more likely to have been diagnosed with GDM (4.93% vs 3.72%; adjusted odds ratio [aOR], 1.39; 95% CI, 1.36–1.42) ( Table 3 ). The risk of gestational hypertension/preeclampsia was greater in women who had GWG above IOM guidelines (1-19 lb above guidelines: 5.41% vs 3.23%, respectively; aOR, 1.68; 95% CI, 1.65–1.71; ≥20 lb above guidelines: 9.10% vs 3.23%, aOR, 2.78; 95% CI, 2.82–2.93) ( Table 3 ). Similarly, the odds of eclampsia was higher with GWG 1-19 lb or ≥20 lb above the IOM guidelines (1-19 lb above guidelines: aOR, 1.55; 95% CI, 1.42–1.70; ≥20 lb above the IOM guidelines: aOR, 2.51; 95% CI, 2.27–2.78) ( Table 3 ). In contrast, women who gained below the guidelines were less likely to undergo induction of labor or cesarean delivery, be diagnosed with chorioamnionitis, require antibiotics use, or be admitted to the ICU. Women who gained above the IOM guidelines were more likely to have obstetric interventions and maternal morbidity ( Table 3 ).
| Variable | Below | Within | 1–19 lb above | ≥20 lb above | Below aOR (95% CI) | 1–19 lb above aOR (95% CI) | ≥20 lb above aOR (95% CI) |
|---|---|---|---|---|---|---|---|
| GHTN or preeclampsia | 2.85% | 3.23% | 5.41% | 9.10% | 0.88 (0.86–0.91) | 1.68 (1.65–1.71) | 2.78 (2.82–2.93) |
| Eclampsia | 0.11% | 0.11% | 0.18% | 0.30% | 0.96 (0.85–1.08) | 1.55 (1.42–1.70) | 2.51 (2.27–2.78) |
| Induction of labor | 26.7% | 27.8% | 32.6% | 38.6% | 0.95 (0.94–0.96) | 1.23 (1.22–1.24) | 1.56 (1.54–1.57) |
| Cesarean delivery | 20.9% | 22.8% | 28.9% | 37.6% | 0.90 (0.89–0.91) | 1.41 (1.40–1.42) | 2.16 (2.14–2.19) |
| Chorioamnionitis | 2.10% | 2.64% | 2.92% | 2.85% | 0.79 (0.77–0.81) | 1.16 (1.13–1.18) | 1.19 (1.16–1.22) |
| Antibiotics use | 19.2% | 19.6% | 22.0% | 24.9% | 0.96 (0.95–0.97) | 1.15 (1.14–1.16) | 1.33 (1.32–1.34) |
| Blood transfusion | 0.21% | 0.22% | 0.25% | 0.27% | 0.96 (0.88–1.05) | 1.11 (1.04–1.19) | 1.22 (1.11–1.33) |
| Maternal ICU admit | 0.08% | 0.10% | 0.09% | 0.09% | 0.73 (0.64–0.84) | 0.93 (0.84–1.04) | 0.97 (0.84–1.12) |
| Gestational DM | 4.93% | 3.72% | 3.28% | 3.26% | 1.39 (1.36–1.41) | 0.92 (0.91–0.94) | 0.99 (0.96–1.01) |
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