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ORIGINAL RESEARCH |
From the Section of Maternal Fetal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Address reprint requests to: Mary L. Khine, MD Department of Obstetrics and Gynecology NYU Downtown Hospital 170 William Street, 8th Floor New York, NY 10038
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Abstract |
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Methods: Six hundred thirty-two adolescents were identified from 11,486 deliveries in our institution through International Classification of Diseases (9th edition) codes. Eleven of those adolescents had GDM. Their charts and those of a representative group of nondiabetic adolescent gravidas were analyzed for GDM risk factors, including race/ethnicity, body mass index (BMI), family history of diabetes, other medical disorders, and previous history of GDM, macrosomia, stillbirths, or anomalous fetus. Statistical analyses used 
2 and Student t tests as appropriate.
Results: The prevalence of GDM among adolescent gravidas was 1.7%. No difference was identified between the adolescent pregnancies with GDM and the comparison group for race/ethnicity, family history, or presence of medical disorders. Risk factors requiring a previous obstetric history could not be evaluated adequately because of the high prevalence of nulliparas. There was a higher prevalence of BMI over 27 in adolescents with GDM (P < .001).
Conclusion: Body mass index is an important risk factor for the development of gestational diabetes in adolescent gravidas. We recommend that selective screening for GDM of adolescent gravidas be performed on the basis of BMI.
Screening for gestational diabetes mellitus (GDM) has become standard practice in obstetrics. It was initially instituted to detect women who developed glucose intolerance during pregnancy,1 presumably because of the influences of human placental lactogen, cortisol, somatomedins, and other diabetogenic hormones altered by pregnancy.2 O’Sullivan and Mahan1 proposed criteria for the diagnosis of GDM in 1964 in an effort to identify women at risk for subsequently developing overt diabetes. These criteria have been adapted to identify women at risk for adverse perinatal outcome.3 Although GDM screening has become standard practice, it is not known how adverse perinatal outcome associated with GDM has been affected by its identification or treatment. Consequently, the topic of how to screen and whom to screen has been an area of unresolved debate.
The ACOG recommended selective screening for GDM based on the presence of maternal risk factors for patients less than 30 years of age.4 The Third International Workshop and Conference on Gestational Diabetes and the American Diabetes Association recommended universal screening of all pregnant women.5 In support of the latter position, several investigators reported that up to 50% of women with GDM would have been missed if they were screened only on the basis of clinical or historic risk factors.6–8 Despite ACOG recommendations, 97% of responding residency directors and Maternal Fetal Medicine fellowship directors advocated universal screening.9 Similarly, more than 75% of recent residency graduates and ACOG Junior Fellows practiced universal screening themselves.10 Whether universal screening leads to fewer clinically significant perinatal complications is unknown.
O’Sullivan and Mahan1 that perinatal mortality was not significantly higher in women who were slim and under the age of 25 years. Because the incidence of GDM increases with maternal age, those at the youngest reproductive ages are at lower risk for GDM. This suggests that the ideal patients for selective screening are those in low-risk populations, such as in adolescents.11
The American Diabetes Association recently published new recommendations for GDM screening.12 They now state that selective screening along clinical guidelines is acceptable for patients younger than 25 years old. These guidelines are expansive. Although race/ethnicity, body habitus, and family and obstetric history have been clinically useful as risk factors, they might not be uniformly reliable in every patient population.
There are few data on the most efficient way to screen selectively. Gestational diabetes mellitus might not be a clinically significant contributor to maternal or perinatal morbidity or mortality in adolescents and therefore might not warrant the resources consumed by universal screening. These resources might better benefit programs that are designed to deter the problem of teenage pregnancy. We performed this study to identify appropriate risk factors for gestational diabetes in adolescent gravidas.
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Materials and Methods |
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Subjects were identified by searching the hospital database for women admitted as of October 1, 1995. All International Classification of Disease (9th edition) codes for hospital discharges between October 1, 1995 and June 30, 1997 were scanned, in search of the diagnosis of gestational diabetes or abnormal glucose tolerance and vaginal or cesarean delivery. Demographic data for diabetic and nondiabetic patients, such as maternal age, race, and payor status, were also collected and stratified by age group.
The definition of teenage pregnancy is varied. As socioeconomic and perinatal complications exist more frequently in women younger than the age of 19 years,14 we included gravidas less than 19 years old at the time of prenatal care registration. The patient’s weight, reported height at the initial prenatal visit (or reported prepregnancy values if first prenatal visit values were unavailable), family history, medical history, and obstetric history were recorded. Significant intrapartum events were noted. Birth weight, length of stay in nursery, evidence of hypoglycemia, and adverse perinatal outcome of the infants were collected.
Appropriate sample size was calculated after data were obtained, as the prevalence of GDM in our adolescent population was unknown before the study. As the prevalence of cases was low, unequal sample sizes were required. Although the statistical power was not significantly improved by increasing the number of control patients, 32 control subjects for each case of GDM were analyzed.
The control group consisted of 352 adolescent gravidas who were part of a previously existing database of adolescent patients who presented for obstetric care between January 1995 and January 1996. This database had been established as a reference group for another investigation. It was believed to be appropriate for the present study because it included every adolescent gravida registered to the hospital in 1995. The only subjects that we excluded from analysis were those with pregestational or gestational diabetes. The remainder of the nondiabetic adolescent gravidas admitted between October 1995 and July 1997 were not reviewed because the number of existing cases within the database was sufficient to grant an 
of .05 and a ß of .80 to detect a difference of 20% in mean body mass index (BMI) in light of the unequal sample sizes (nine study patients recommended).
Statistical analysis was done using the 2 test and Fisher exact test where appropriate. The Yale Human Investigation Committee approved the protocol.
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Results |
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. Of 11,486 deliveries at our institution over the study period, 556 (4.8%) were complicated by gestational diabetes. There was no statistical difference of the incidence of GDM within racial/ethnic groups when stratified by payor status.
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In all adolescents, diabetes was controlled by diet alone. Four reported other medical disorders (all asthma), but none required long-term steroid medication.
Four women (36%) reported a history of diabetes in a first- or second-degree relative, compared with 21% in the comparison group (P = .059). Excluding body habitus and race, nearly 80% of our adolescent population lacked historic risk factors for gestational diabetes.
The mean ± standard deviation BMI of the gestational diabetics was 29.52 ± 4.92 compared with 23.03 ± 4.68 in our comparison group. According to the 1985 National Institutes of Health Consensus Panel on Obesity, obesity may be defined as BMI greater than the 85th percentile, nationally, 27.3 for younger women.15 In the study population, the 85th percentile was 27.2, which represents nearly one standard deviation above the mean. Nine of the adolescent subjects with GDM had a BMI greater than 27.2 based on their weight and reported height at initial prenatal examination or on reported prepregnancy height and weight (Table 4
). Among nondiabetic adolescents, only 16% had BMI greater than 27 compared with 82% in the gestational diabetic group (P < .001).
Because 92% (10) of the adolescents in the GDM group and 88% of the adolescents in the comparison group (P = nonsignificant) were nulliparous, obstetric history could not be evaluated.
Ten of the eleven infants of diabetic adolescents were delivered at term. One was delivered at 35 weeks due to preeclampsia. Two pregnancies were delivered by cesarean, one for secondary arrest of labor at 6 cm (birth weight 4355 g) and the other for breech presentation (birth weight 3340 g). Of the remaining pregnancies, two neonates had mild shoulder dystocia without neurologic impairment reported on newborn examination. The birth weights of these fetuses were 4190 g and 4410 g.
All infants were discharged to the care of their mothers on the day of maternal discharge, except for one, who remained an extra 4 days for completion of a septic workup (patient 1). Only one infant had hypoglycemia requiring intravenous glucose (patient 11). That infant was released home with the mother and did not require a prolonged stay in the nursery. There were no cases of clinically apparent electrolyte disorders or hyperbilirubinemia.
Four infants in the GDM group weighed more than 4000 g. The mean birth weight of approximately 3710 g for the infants of diabetic mothers was not significantly different from the mean birth weight of 3090 g for the infants born to the comparison group (P > .05).
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Discussion |
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Other studies examined the importance of risk factors in detecting gestational diabetes,3,6–8,18,19 but few uniformly examined both age and BMI. Some studies even excluded obese subjects from the analysis.7 Sacks et al20 reviewed plasma glucose values of 3505 pregnant women given a 75-g, 2-hour glucose tolerance test (World Health Organization recommendations) and found positive correlation between fasting, 1-hour, and 2-hour values and maternal age, parity, and prepregnancy BMI. Naylor et al21 recently proposed a clinical risk factor scoring system as a means of GDM screening. Although they found a statistically significant increase in the incidence of GDM with advancing age of the patient, they only included women who were at least 25 years old. Race, increasing age, and higher BMI were the most statistically significant risk factors for GDM. In the present study, age and race seem to be significant co-risk factors for older age groups but less important in the younger age group. We interpret the poor association of race/ethnicity and the development of gestational diabetes in our data with caution, as our small study group might not appropriately represent a larger population.
The overall prevalence of gestational diabetes in our adolescent population was 1.7% compared with the general population prevalence of 4.8%. The prevalence of gestational diabetes in our general obstetric population was within the range reported in the literature (2.0–6.3%).18 In 1989, Coustan et al18 reported a prevalence of 0.7% in patients less than 20 years old, with an overall GDM rate of 2%. Demographic differences in the two populations (our population consisted of a larger percentage of Asian and Hispanic patients) might have contributed to that difference, although it is most likely because Coustan et al used the National Diabetes Data Group’s criteria to identify gestational diabetics.
Weeks et al7 reported that the most common risk factors in patients with gestational diabetes were family history of diabetes (45%), previous macrosomic infant (43%), and prior gestational diabetes (30%). Because most of the adolescents were nulliparous, prior obstetric history was not a useful factor. Other risk factors frequently cited, such as presence of other medical disorders, fetal anomalies, and glycosuria, were not noted at an increased frequency in adolescents with GDM compared with controls. Family history of a first-or second-degree relative with diabetes might be a useful adjunct in selecting a subset for screening because the prevalence of a positive family history in our adolescent population approached statistical significance (P = .059).
Because of the retrospective nature of the study, we relied on data gathered by a large group of people with different levels of history-gathering expertise, including attending physicians, house staff, several nurses, nurse practitioners, and students. A prospective study might control for some of those variables. The absence of some risk factors in our study could be a function of recall bias (younger subjects frequently are unaware of complete family histories) and the prevalence of nulliparous women (88%) in this adolescent population.
Maternal BMI greater than 27 in nine (82%) of 11 adolescents with GDM contrasts with the overall prevalence of 16% in the comparison population (P < .001). Body mass index higher than 27 is useful in identifying adolescents at greater risk for having abnormal results of glucose challenge and tolerance testing. We recommend screening for gestational diabetes in adolescent gravidas with BMI greater than 27. When a cutoff BMI of greater than 27 was used, 82% of patients in whom GDM was eventually diagnosed by conventional screening would be identified; the negative predictive value is 99.4%.
Universal screening, particularly in younger patients, could be supported by possible detection of undiagnosed pregestational diabetes. Although this is of concern, none of our small cohort of diabetic adolescents had diabetes postpartum. Additionally, none of them required insulin, whereas other studies have predicted that 15–17% of gestational diabetics would require insulin to maintain optimal glycemic control.2 The reason for this may be due to our exclusion of older gestational diabetics, who may have less insulin reserve.
The incidence of GDM in any given population could be 15% higher using Carpenter and Coustan’s screening and diagnostic cutoffs compared with those proposed by ACOG and the National Diabetes Data Group.13 In the 1-hour glucose challenge tests in our study population, 5% had 1-hour postglucose load values between 130 and 139, which indicates that the incidence of GDM in our population might be overestimated. We believe that this result is not significant because the control population was evaluated using the same criteria and the evaluation of risk factors for GDM was independent of the cutoffs.
We could not determine whether perinatal outcome was improved with treatment of GDM in adolescent pregnancies in the present study because the number of diabetic adolescents was too small to draw significant outcome conclusions.
Because of the low prevalence of gestational diabetes in this age group, a case-control design was most appropriate. However, this design also represents the largest weakness to this study, as the conclusions were based on record review of a small number of cases. We increased the power to detect a difference between the control and study groups by using a large number of controls for each case of adolescent GDM. Nonetheless, conclusions concerning large demographic variables such as race are made with caution as just one or two additional subjects in the study group could influence the statistical analysis. The importance of examining all variables in this study is the acknowledgment of trends.
The overall prevalence of gestational diabetes is low in the adolescent population, making selective screening attractive. Traditional risk factors, such as personal history of diabetes, obstetric history, or presence of other medical disorders, were not helpful in our young population. We did not find race/ethnicity helpful in identifying patients more likely to have diabetes during pregnancy. Family history of diabetes was not found statistically more frequently in the study population compared to the control population, although there was a trend toward statistical significance. Nine of eleven adolescent gravidas with GDM reported early pregnancy BMI greater than 27, suggesting that a BMI of 27 or more might be the most useful criterion for identifying patients most likely to benefit from diabetes screening.
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Footnotes |
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Received June 29, 1998. Received in revised form October 26, 1998. Accepted October 29, 1998.
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References |
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2. Moore TR. Diabetes in pregnancy. In: Creasy RK, Resnik R, eds. Maternal fetal medicine: Principles and practice, 3rd ed. Philadelphia: WB Saunders, 1994:934–77.
3. O’Sullivan JB, Charles D, Mahan CM, Dandrow RV. Gestational diabetes and perinatal mortality rate. Am J Obstet Gynecol 1073;117: 901–4.
4. American College of Obstetricians and Gynecologists. Management of diabetes in pregnancy. ACOG technical bulletin no. 200. Washington DC: American College of Obstetricians and Gynecologists, 1994.
5. Third International Workshop Conference on Gestational Diabetes Mellitus. Summary of recommendations of the third international workshop conference on gestational diabetes. Diabetes 1991; 40(Suppl):197–201.[Abstract]
6. O’Sullivan JB, Mahan CM, Charles D, Dandrow RV. Screening criteria for high risk gestational diabetic patients. Am J Obstet Gynecol 1973;116:895–900.[Medline]
7. Weeks JW, Major CA, deVeciana M, Morgan MA. Gestational diabetes: Does the presence of risk factors influence perinatal outcome? Am J Obstet Gynecol 1994;171:1003–7.[Medline]
8. Magee MS, Walden CE, Benedetti TJ, Knops RH. Influence of diagnostic criteria on the incidence of gestational diabetes and perinatal morbidity. JAMA 1993;269:609–15.[Abstract]
9. Owen J, Phelan ST, Landon MB, Gabbe SG. Gestational diabetes survey. Am J Obstet Gynecol 1995;172:615–20.[Medline]
10. Landon MB, Gabbe SG, Sachs L. Management of diabetes mellitus and pregnancy: A survey of obstetricians and maternal fetal medicine specialists. Obstet Gynecol 1990;75:635–40.
11. American Diabetes Association. Clinical practice recommendations 1998—Position statement, gestational diabetes mellitus. Diabetes Care 1998;21:s1–9.
12. Coustan DR. Screening and testing for gestational diabetes mellitus. Obstet Gynecol Clin North Am 1996;23:125–36.[Medline]
13. Carpenter MW, Coustan DR. Criteria for screening tests for gestational diabetes. Am J Obstet Gynecol 1982;144:768–73.[Medline]
14. Hollingsworth DR, Kreutner AK. Sounding board. Teenage pregnancy: solutions are evolving. N Engl J Med 1980;303:516–8.[Medline]
15. Cunningham FG, MacDonald PC, Gant NF, Leveno KJ, Gilstrap LC III, Hankins GDV, et al. Williams obstetrics. 20th ed. Stamford, Connecticut: Appleton & Lange, 1997.
16. The Expert Committee on the Diagnosis and Classification of Diabetes Mellitus. Report of the expert committee on the diagnosis and classification of diabetes mellitus. Diabetes Care 1998;211:s5–19.
17. Jarrett RJ. Gestational diabetes: A non-entity? BMJ 1993;306:37–8.
18. Coustan DR, Nelson C, Carpenter MW, Carr SR, Rotondo L, Widness JA. Maternal age and screening for gestational diabetes: A population based study. Obstet Gynecol 1989;73:557–60.
19. Rodriguez H, Neiger R, Thompson S, List M, Krohn H. Screening adolescent gravidas for gestational diabetes. Adoles Pediatr Gynecol 1995;8:125–7.
20. Sacks DA, Greenspoon JS, Abu-Fadil S, Henry H, Wolde-Tsadik G, Yao JFF. Toward universal criteria for gestational diabetes: The 75 gram glucose tolerance test in pregnancy. Am J Obstet Gynecol 1995;172:607–14.[Medline]
21. Naylor CD, Sermer M, Chen E, Farine D (for the Toronto Tri-hospital Gestational Diabetes Project Investigators). Selective screening for gestational diabetes mellitus. N Engl J Med 1997;337:1591–6.
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