Gestational diabetes and pregnancy-related hypertension are associated with adverse health effects among both mothers and infants. Gestational diabetes increases the risk for preterm and cesarean delivery and type 2 diabetes in the mother (1-5) and macrosomia, hyperinsulinemia, and future obesity and diabetes in the infant (4,6-9). Pregnancy-related hypertension increases the risk for preterm and cesarean delivery, renal dysfunction, placental abruption, chronic hypertension, and death in the mother (10-12) and respiratory distress syndrome and fetal growth restriction in the infant (10,13,14). Gestational diabetes occurs in approximately 4% of pregnancies and ranges from 1% to 14% among different racial/ethnic groups (15). Asian and Hispanic mothers have the highest rates, whereas white mothers have the lowest (16-19). The prevalence of pregnancy-related hypertension ranges from 6% to 8% and also varies by race/ethnicity; black mothers have the highest rates and white mothers have the lowest (12,13,19).

Several studies have shown that the prevalence of gestational diabetes has increased (16,17,20), but only one population-based study has described trends in pregnancy-related hypertension (21). No studies have investigated trends in both conditions over time while also considering racial/ethnic and age distributions. We investigated whether the rates of gestational diabetes and pregnancy-related hypertension are on the rise in Los Angeles County, California, which has a large, urban population with substantial racial/ethnic diversity.

From 1991 through 2003, a total of 2,156,459 Los Angeles County residents were hospitalized for a singleton delivery. The number of residents with singleton births declined from 1991 to 2003, which reflected a decline in the birth rate rather than a decrease in the number of women of childbearing age. The racial/ethnic distribution of women who gave birth changed over the course of the study period: Hispanics accounted for an increasing percentage and whites accounted for a decreasing percentage of women giving birth (Table 1).

The age distribution of women who gave birth also changed during the study period. Women aged 15–24 accounted for a smaller percentage of women who gave birth in 2003 than in 1991, whereas women aged 35–54 accounted for a larger percentage in 2003 than in 1991 (Table 1). This trend toward increasing maternal age was observed in all racial/ethnic groups.

Our findings demonstrate that age-adjusted prevalences of gestational diabetes and pregnancy-related hypertension increased among women in Los Angeles County from 1991 through 2003. The increase in rates of gestational diabetes was especially pronounced and was higher than that observed in another large, multiethnic population study (20). However, this latter study was done in a private health-maintenance organization population that may have had greater access to prenatal care than did women in our study, which included women without health insurance as well as those with public and private insurance.

We found increases in gestational diabetes and pregnancy-related hypertension among all racial/ethnic and age groups studied. However, the age-adjusted rates of gestational diabetes were highest among Hispanic and Asian/Pacific Islander mothers and lowest among white mothers, whereas the age-adjusted rates of pregnancy-related hypertension were highest among black mothers and lowest among Asian/Pacific Islander mothers. These racial/ethnic differences are consistent with findings of previous studies (18,23-25). Older mothers had higher rates of both conditions than did their younger counterparts, which is also consistent with other studies (14,15,25).

The observed increases in gestational diabetes and pregnancy-related hypertension from 1991 through 2003 persisted after controlling for age and race/ethnicity in multivariable analyses. The race/ethnicity-specific rate increase was highest for gestational diabetes among Hispanic mothers and highest for pregnancy-related hypertension among black mothers. The highest age-specific rate increase of gestational diabetes was observed among the youngest age group (15–24 years) of Asian/Pacific Islander mothers, and similarly, the highest rate increase of pregnancy-related hypertension was observed among the youngest age group of black mothers.

Our study had several strengths. First, our data captured nearly all births in Los Angeles County, a large and highly diverse population, during a 13-year period. Second, this study is, to our knowledge, the first to report population-based trends in both gestational diabetes and pregnancy-related hypertension. Third, we controlled for race/ethnicity and age in the analysis and analyzed trends separately for each racial/ethnic and age group. Because race/ethnicity and age are strong risk factors for both conditions, understanding how the rates change independently of these factors is important given the change in racial/ethnic demographics in Los Angeles and the increasing proportion of births among older women.

Other studies have reported increases in the prevalence of gestational diabetes, including racial/ethnic disparities (16,17,20,26) and a greater relative increase in prevalence among younger women (17). However, only one of these studies captured information on all mothers who gave birth in the target population, and this study did not control for race/ethnicity or age (17). One previous study investigated trends in hypertensive diseases in pregnancy and found, in contrast to our findings, a decrease in these conditions (21). However, that study relied solely on birth certificate data, which may be less sensitive than hospital discharge data or medical record review in identifying cases (27).

Our study had several limitations. First, the diagnoses were based on hospital discharge codes and did not include medical chart review. Though hospital discharge records have been reported to accurately determine rates of gestational diabetes (28), we cannot rule out the possibility that the observed increases may have been due to increased coding of gestational diabetes and pregnancy-related hypertension as discharge diagnoses because of change in hospital policies or coding errors. A second limitation is that we could not directly assess the degree to which increased screening or changes in diagnostic criteria might have influenced our findings. However, diagnostic criteria and screening guidelines did not change during our study (29-31), so this limitation is unlikely to substantially bias our findings. A third limitation is that we did not have data on other factors that may have contributed to an increase in gestational diabetes and pregnancy-related hypertension, in particular data on maternal weight. During the past decade, the prevalence of obesity has increased among women of childbearing age in the United States and in Los Angeles County (32,33, M. Shih, written communication, April 2006), and obesity increases the risk of gestational diabetes and pregnancy-related hypertension by as much as 5-fold (15,17,23,33). Our results are consistent with other research that has found a parallel increase in gestational diabetes and obesity prevalence among women of childbearing age in a large, urban setting (17). Further research is needed to determine the degree to which the obesity epidemic might be contributing to an increase in rates of gestational diabetes and pregnancy-related hypertension. Our findings highlight the need for enhanced surveillance of gestational diabetes, pregnancy-related hypertension, and maternal weight. This surveillance could be accomplished through medical record review at sentinel health care sites or collection of data on birth certificates.

Our findings also underscore the need to further investigate the racial/ethnic disparities in the prevalence rates and rate increases of gestational diabetes and pregnancy-related hypertension. Our results are consistent with findings that minority women are at higher risk of gestational diabetes (16-19) and pregnancy-related hypertension (12,13,19). The causes of the disproportion are unclear, although biological, cultural, and socioeconomic factors may all play a role. One study found that the biological response to lipid and carbohydrate metabolism in Asian-born women puts them at higher risk of gestational diabetes compared with white women (18). Another study found that maternal and paternal ethnicity affected the risk of preeclampsia. Women whose mothers were black or whose parents were of different races or ethnicities were at increased risk of preeclampsia, whereas those whose fathers were Asian had the lowest risk, which suggests a possible genetic or cultural influence or combination of the two (25). Socioeconomic and cultural factors may also predispose nonwhite or Hispanic women to unhealthful diets and obesity (17) and reduce access to prenatal care (34). However, other research found that even after controlling for early access to prenatal care, minority women were still more likely to have poor perinatal outcomes, including gestational diabetes and preeclampsia (35), which suggests that health care access and healthy lifestyle are crucial even before conception (36).

Health care systems should ensure that women have timely access to preconception and prenatal care that effectively addresses risks for and management of gestational diabetes and pregnancy-related hypertension. Early identification and clinical management of women at risk for these conditions is critical. Health care providers should counsel women at risk on prevention measures such as nutrition, weight and stress management, and early and continual monitoring of gestational diabetes and pregnancy-related hypertension throughout the pregnancy. Community education efforts for women of childbearing age are also needed to reinforce the importance of healthy diets, regular physical activity, and maintaining a healthy weight before and during pregnancy.