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Pregnancy Nutrition Surveillance System

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What is PNSS?

The Pregnancy Nutrition Surveillance System (PNSS) is a program-based public health surveillance system that monitors risk factors associated with infant mortality and poor birth outcomes among low-income pregnant women who participate in federally funded public health programs.

 

PNSS Health Indicators

Data on maternal health and behavioral risk factors and infant birth outcomes are collected on low-income women who participate in federally funded public health programs. Maternal health indicators include prepregnancy weight status, maternal weight gain, parity, interpregnancy intervals, anemia, and diabetes and hypertension during pregnancy. The behavior risk factors assessed are medical care, WIC Program enrollment, multivitamin consumption, smoking and drinking. Birth outcome data includes birthweight, preterm births, full term low birthweight and breastfeeding initiation. PNSS health indicators are collected during prenatal and postpartum clinic visits to monitor the prevalence of nutrition and behavioral risk factors related to infant mortality and poor birth outcomes. The definition for each indicator and the rationale for collecting the indicator are described below:

Maternal Health Indicators

Prepregnancy BMI
Maternal Weight Gain
Anemia
Parity
Interpregnancy Interval
Gestational Diabetes
Hypertension During Pregnancy

Maternal Behavioral Indicators

Medical Care
WIC Enrollment
Multivitamin Consumption

Smoking/Drinking Indicators

Smoking
Smoking Changes
Smoking in Household
Drinking

Infant Health Indicators

Birthweight
Preterm Birth
Full term Low Birthweight
Breastfeeding Initiation



Maternal Health Indicators

Prepregnancy Body Mass Index (BMI) is a measure of weight for height expressed as wt (kg) / ht (m2) before the woman became pregnant. The BMI cut-off values specified by the Institute of Medicine (IOM) in 2009 are commonly used to classify women as underweight, normal weight, overweight, and obese prior to pregnancy. Prepregnancy BMI is a determinant of weight gain during pregnancy and birthweight (IOM, 2009).

Prepregnancy Weight

BMI

Underweight

<18.5

Normal weight

18.5–24.9

Overweight

25.0–29.9

Obese

≥30

Maternal Weight Gain also called gestational weight gain refers to the amount of weight gained from conception to delivery. In 2009 the IOM published recommended weight gain amounts based on prepregnancy BMI for optimal infant health. Maternal weight gain is based on prepregnancy weight status and is considered to be a major determinant of birthweight as well as infant mortality and morbidity.

Weight

Prepregnancy BMI

Total Weight Gain (lb)

Underweight

<18.5

28–40

Normal weight

18.5–24.9

25–35

Overweight

25.0–29.9

15–25

Obese

≥30

11–20

Prepregnancy Weight

< Ideal Weight Gain (lb)

Underweight

<28

Normal weight

<25

Overweight

<15

Obese

<11

Prepregnancy Weight

> Ideal Weight Gain (lb)

Underweight

>40

Normal weight

>35

Overweight

>25

Obese

>20

 

Anemia during pregnancy is defined as less than the 5th percentile of the distribution of hemoglobin (Hb) or hematocrit (Hct). The distribution and cut off values are based on data obtained from clinical studies of European women who had taken iron supplements during pregnancy. (MMWR, 1998). The cut off values vary by trimester for pregnant women and are different from nonpregnant women. For nonpregnant women, anemia cut off values are established below the 5th percentile of the distribution of Hb or Hct from the third National Health and Nutrition Examination Survey for a healthy population. Trimester and age specific cut off values used in PNSS are shown below for pregnant and nonpregnant women, respectively. Because persons residing at higher altitudes have higher hematology levels, in PNSS Hb or Hct values are automatically adjusted for altitude.

Pregnancy Trimester

Hemoglobin

Hematocrit

First

11.0

33.0

Second

10.5

32.0

Third

11.0

33.0

Postpartum Age

Hemoglobin

Hematocrit

12 - < 15 yrs

11.8

35.7

15 - < 18 yrs

12.0

35.9

≥ 18 yrs

12.0

37.7

Pregnant women are at a higher risk for iron deficiency anemia because of the increased iron requirements of pregnancy. In pregnant women hemoglobin (Hb) or Hematocrit (Hct) levels drop during the first and second trimester because of blood volume expansion. Among pregnant women who do not take iron supplements Hb and Hct remain low during the third trimester. Longitudinal studies have shown that the highest prevalence of anemia during pregnancy is in the third trimester; therefore, the Healthy People 2010 objective monitors the prevalence of anemia during the third trimester of pregnancy. This objective seeks to reduce anemia in the third trimester among low income women from its baseline of 29 percent in 1996 to 20 percent in 2010. Pregnant women who have adequate iron intake have a gradual rise in Hb and Hct during the third trimester toward the prepregnancy levels (MMWR, 1998). Changes in the prevalence of anemia over time can be used to evaluate the effectiveness of programs designed to decrease the prevalence of iron deficiency. 

The analysis of postpartum anemia includes only records with valid Hb and Hct measurements taken at greater than 4 weeks or 28 days postpartum when Hb and Hct measurements are expected to return to prepregnancy or first trimester levels. After delivery, maternal hemoglobin is expected to increase as the expanded red cell mass of pregnancy contracts and iron returns to body stores.

Parity refers to the number of times a woman has been pregnant for 20 or more weeks regardless of whether the infant is dead or alive at birth (The current pregnancy is not included.). Parity, or the number of previous pregnancies, has been shown to impact the long-term health status of women and pregnancy outcomes, specifically birthweight, for some groups. A number of studies show that first-born children have a lower mean birthweight and are at greater risk of low birthweight than subsequent children (Kramer, 1987; Cogswell and Yip, 1995; Macleod and Kiely, 1988; IOM, 1985,). Multiparity at a young age (under 20 years) increases the risk of delivering a low birthweight baby (IOM 1996; Kramer 1987) and increased parity is associated with excessive maternal postpartum weight retention (Parker and Abrams, 1993) and with iron deficiency (Looker et. al. 1997).

Interpregnancy Interval is considered to be the amount of time between pregnancies and is calculated as the number of months between the date the last pregnancy ended and the date of the last menstrual period. Women with short interpregnancy intervals are at nutritional risk and more likely to experience adverse birth outcomes. Studies conducted by Lieberman and colleagues showed that women with an interpregnancy interval less than 18 months were at greater risk of delivering a full term small for gestational age (low birthweight) infant compared to women with interpregnancy intervals of 24 to 36 months. (IOM, 1996) Furthermore, interpregnancy interval of 3 months has been shown to result in an increase in the risk of delivery of a pre-term or small for gestational age infant as well as neonatal death. Shorter interpregnancy intervals also mean a shorter time for repletion of nutrient stores. (IOM, 1996)

Gestational diabetes refers to the presence of a type of diabetes that occurs during pregnancy (usually during the second or third trimester), if the body does not produce enough insulin to meet the extra needs of pregnancy. Gestational diabetes increases the risk of complications during pregnancy. Women with gestational diabetes are at risk of delivering macrosomic infants and developing type II diabetes later in life. (IOM, 1996) It is estimated that 2 to 3 percent of pregnant women will develop gestational diabetes. (IOM, 1996) A developmental health objective for 2010 has been established to decrease the proportion of pregnant women with gestational diabetes.

Hypertension refers to the presence of chronic hypertension or pregnancy induced hypertension. Hypertension is defined as an elevated arterial blood pressure. (NRC,1989) In adults hypertension is classified as a systolic pressure greater than 140 mm Hg and a diastolic pressure above 90 mm Hg. (WHO, 1978) Women with chronic hypertension prior to pregnancy are more likely to experience adverse pregnancy outcomes such as fetal growth restriction and abruptio placentae. (IOM, 1996) Pregnancy induced hypertension occurs in 5-9 percent of women and can lead to preeclampsia, eclampsia, and ultimately preterm delivery, fetal growth retardation, abruption placentae, and fetal death. (Zhang et. al. 1997) 




Maternal Behavioral Indicators

Medical Care indicates the month in which prenatal care began for the current pregnancy. Medical care data are always collected at the prenatal visit. It must be collected at the postpartum visit if the woman was not enrolled in the program participating in the PNSS while she was pregnant or if she reported at the prenatal visit that she had not begun medical care. The American College of Obstetricians and Gynecologists (ACOG) has established guidelines in Standards for Obstetric-Gynecologic Service to monitor the progress of the mother and developing fetus, which call for early entry into care with at least 13 visits during a full-term pregnancy. (Healthy People 2010) Women who begin prenatal care after the first trimester are at a higher risk for poor pregnancy outcomes with infants being born premature, low birthweight or growth retarded. (Alexander and Korenbrot, 1995; IOM, 1990; USDA, 1991) Although a large proportion of women receive early and adequate prenatal care, there is great variation across racial ethnic groups and among some age groups. (Healthy People 2010) Consequently, DHHS continues its health objective for 2010 to increase to 90 percent the proportion of women who receive early and adequate prenatal care. (Healthy People 2010).


WIC Enrollment is defined as the date the woman enrolled in WIC for the current pregnancy. This indicator is used to determine the length of WIC exposure for this pregnancy, which is related to birth outcome. A number of studies considering WIC participation, low birthweight and prematurity concluded that prenatal WIC participation is associated with improved birthweights and a reduction in pre-term delivery. (Devaney et. al 1992, Abrams, 1993). Additionally, Ahluwalia et. al. concluded that WIC participation resulted in a reduction in small for gestational age deliveries. Furthermore, longer enrollment in WIC program was associated with a reduced risk of small for gestational age delivery. (Ahluwalia,1998) 

Multivitamin Consumption refers to the intake of multivitamin supplements containing the recommended amounts of folic acid prior to pregnancy and iron during pregnancy.

Smoking/Drinking Indicators

Smoking During Pregnancy refers to the active use of cigarettes. It is associated with an increased risk for low birthweight delivery, spontaneous abortion, sudden infant death syndrome as well as long-term negative effects on growth and development, behavior and cognition of the infant. (IOM, 1996, Healthy People 2010) Healthy People 2010 calls for an increase in smoking cessation during pregnancy during the first trimester of pregnancy. (HP 2010)

Cigarette smoking 3 months prior to pregnancy indicates the number of women who reported smoking any number of cigarettes during the 3 months before pregnancy and is used to determine smoking cessation. According to the Surgeon General's report on the benefits of smoking cessation, women who discontinue smoking prior to becoming pregnant deliver babies of the same birthweight as women who never smoked. (Surgeon General, 1990)*

Smoking Changes are health indicators that show changes in the smoking behaviors of women that smoked cigarettes prior to pregnancy and quit by the first prenatal visit.

Smoking In Household refers to the exposure to tobacco-contaminated air at home. This indicator assesses whether anyone in the household other than the pregnant woman smoked at the time of her prenatal visit. A study on the exposure to tobacco smoke among young infants (6 -8 weeks old) living in homes where one member of the family other than the mother smoked showed higher levels of cotinine compared to infants not exposed to smoking. (Chilmonczyk, 1990) Infants and children exposed to particles from secondhand smoke are at risk for impaired health, growth and development. Exposure to tobacco smoke is associated with lower and upper respiratory problems and asthma. (IOM, 1996) A recent review (Misra and Nguyen, 1999) indicates that mothers exposed to environmental tobacco smoke were 1.5 – 4 times more likely to deliver infants who were low birthweight or small-for-gestational age than mothers who were not exposed.


Drinking refers to the use or consumption of alcohol during pregnancy. Alcohol is rapidly absorbed and enters fetal circulation and maternal milk. Pregnant women who consume more than 6 ounces of liquor (or the equivalent) per day have a 20 percent chance of having a child with Fetal Alcohol Syndrome (FAS). (Benson and Pernell, 1994). Adverse physical and neurological problems may occur at lower levels of exposure to alcohol. (Bloss, 1994) Healthy People 2010 calls for abstinence from alcohol during pregnancy. Drinking during pregnancy is assessed using the two indicators listed below.


 

Infant Health Indicators

Birthweight

Preterm Birth refers to delivery before 37 weeks gestation. Preterm births are the largest contributor to neonatal, infant and perinatal mortality in the U. S. and can be minimized by preventing problems like anemia and inappropriate weight gain through nutrition intervention. (IOM, 1990, 1996) Other factors related to increased risk of preterm delivery include low income, ethnic background (particularly black), young age, smoking, and low education attainment. (IOM, 1996)


Full Term Low Birthweight refers to infants born at or after 37 weeks weighing less than 2500 grams. This indicator is one of several used to diagnose intrauterine growth retardation or fetal growth restriction. (IOM, 1996) In these infants gestational age is not the issue because the pregnancy is complete; however, poor maternal nutrition is cited as one of the many causes of full term birthweight. (Kessel, 1978, IOM 1996) An infant's size at birth is very important as fetal growth restriction contributes to the risk of respiratory distress, hypoglycemia and other problems. (IOM, 1996) 


Breastfeeding Initiation reports the number of infants ever breastfed or fed breastmilk. The nutritional, immunologic, allergenic, economic and psychological advantages of breastfeeding are well recognized. Breastfeeding is nutritionally superior to any alternative infant feeding method and provides immunity to many viral and bacterial diseases; enhances infants' immunologic defenses; prevents or reduces risk of respiratory and diarrhea diseases; promotes correct development of jaws, teeth and speech patterns; decreases tendency toward childhood obesity and facilitates maternal infant attachment (Jacobi and Levin, 1993; AAP 1997).


From: cdc.gov