The Pregnancy Nutrition Surveillance System (PNSS), conducted by the Centers for Disease Control and Prevention (CDC), is designed to monitor the prevalence of nutrition-related problems and behavioural risk factors which are related to infant mortality and low birth weight. The target population of the PNSS is low-income, high-risk pregnant women who participate in publicly funded health, nutrition and food assistance programmes in the USA. Currently, 17 States and the District of Columbia participate in the PNSS. The data used for analysis came from the 1989 PNSS (births occurred between 1 January through 31 December 1989).
The CDC provides training and technical assistance in support of the PNSS. Personnel at the state and local level are trained in the selection and use of equipment, weighing and measuring techniques, and data interpretation and utilization. The PNSS is a programme-based surveillance system. Agencies participating in the PNSS collect and submit standardized data to CDC.
The coverage of PNSS reflects the number of pregnant women who take part in the clinic-based programmes that contribute information to the surveillance system. The number of records submitted each year to the PNSS has grown from fewer than 10 000 in 1979 to about 160 000 for births occurring in 1989. Of the 29 672 records in the 1989 PNSS which had complete information on the key variables, i.e., birth weight, weight gain during pregnancy, pre-pregnancy weight, maternal height, mother's age, duration of pregnancy, and ethnic background, only the 26 883 records from singleton, live births to White, Black and Hispanic women were selected in order to allow stratification by ethnic background.
We further excluded 2092 records with extreme values on the basis of: duration of pregnancy shorter than 22 weeks or longer than 43 weeks, mother's age below 12 or above 45 years, maternal height below the 1st (142.9 cm) or above the 99th percentile (178 cm), weight gain during pregnancy below the 1st (-6.8 kg) or above the 99th percentile (31.3 kg). The final sample size selected for the analysis was 24 791.
Length of pregnancy was determined from the date of the last menstrual period and the date of delivery. Pre-pregnancy weight was based on either the woman's self-report or an actual measurement if the woman enrolled for programme benefits early in the first trimester.
1. Intrauterine growth retardation (IUGR)
Estimated odds ratios (OR) for IUGR among Black women who are at or below the lowest quartile of height and weight are 1.9 (95% CI, 1.5-2.3) and 1.8 (95% CI, 1.5-2.2).
Women who are at or below the lowest quartile of body mass index (BMI) also had a higher risk of giving birth to an IUGR infant (OR, 1.5; 95% CI, 1.2-1.8) compared to women who are above the lowest quartile. In a subgroup of women with below average height, the risk of IUGR among women who are at or below the lowest quartile of weight or BMI is even greater (OR for weight, 2.7; and OR for BMI, 2.9).
2. Low birth weight (LBW)
The estimated odds ratio of LBW among Black women who are at or below the lowest quartile of height is 1.7 (95% CI, 1.4-2.1). The odds ratio for LBW among women who are at or below the lowest quartile of weight and BMI are 2.3 (95% CI, 1.9-2.8) and 1.8 (95% CI, 1.5-2.2), respectively. In a subgroup of women with below average height, women who are at or below the lowest quartile of weight and BMI are at particularly high risk of LBW with odds ratios of 2.7 and 2.8, respectively.
3. Preterm birth
Maternal body size was significantly associated with an increased risk of preterm birth with an odds ratio of 1.3, 1.6 and 1.4 for women who were at or below the lowest quartile of height, weight and BMI, respectively. The estimated odds ratio of preterm birth among a subgroup of Black women with below average height who are at or below the lowest quartile of weight and BMI was 1. …