An Analysis of Healthy Start Prenatal Screening Data:
Women Who Choose to Be Screened Versus Those Who Do Not
An Analysis of Healthy Start Prenatal Screening Data
Author: Melanie Simmons
HEALTHY START:
Since April, 1992 all pregnant women in Florida are to be offered the Healthy Start
Prenatal Risk screening at their first prenatal visit. This was mandated by the Healthy
Start legislation passed in 1991. The information used for this analysis comes from this
Healthy Start data.
ABOUT THE DATA:
The data used in this analysis are from a linked file. A cohort of 38,587 women who had
a score of 4 or more on the Healthy Start prenatal screening were selected. This cohort of
women were screened between October 1, 1992 and September 30, 1993. The prenatal screening
data on these women was then matched to the birth certificate data and the CIS/HMC service
records. The files were matched to include the same time period as the above plus an
additional nine months in order to capture all of the births from the original cohort of
women. The common data element on the prenatal screen, birth certificate, and CIS/HMC
service records used for matching was the social security number. Of the original 38,587
women, 35,684 had a valid social security number on the prenatal screen. Seventy-nine
percent of those with valid social security numbers were matched to a birth certificate
(28,274 records). Some of the records with matching prenatal screens and birth
certificates were also served in a county public health unit so they had matching CIS/HMC
service records (19,193 records). This analysis was done using the data for the 28,274
women for whom birth records matched the prenatal records and therefore inferences apply
only to women who meet the same criteria. The differences between these women and the
women in the original cohort who did not have matching birth records, should be analyzed
before results are generalized to the original cohort.
The race categories used in this analysis are black and non- black. The prenatal file
only asks whether a woman's race is white, black, or other. Preliminary analysis shows
that the other category is more similar to whites than to blacks. Therefore, in this
analysis I grouped whites and other races into the non-black category.
NON-SMOKERS:
The average low birth weight rate (birth weight less than 2500 grams) for women who did
not smoke was 0.1014 (top left in Table 1). Among the non-smoking portion of the cohort,
there is a large difference between birth weights for non-blacks and blacks. For non-black
non-smokers, the average low birth weight rate was 0.0708, whereas the black non-smokers
average low birth weight rate was 0.1270. Blacks have historically had higher rates of low
birth weight births. This relationship of blacks having lower birth weight babies is
consistent within the smoking population as well.
SMOKERS VERSUS NON-SMOKERS:
For this analysis, smokers were defined as those reporting they smoked at least ten
cigarettes a day on the Healthy Start screen. As shown in Table 1, for all smoking women
the low birth weight rate was 0.1228 which compares to the non-smoking low birth weight
rate of 0.1014. For non-blacks, those who smoked had a low birth weight rate of 0.1114,
while non-blacks who did not smoke had a low birth weight rate of 0.0708. For blacks, the
rate for those who smoked was significant and much higher than for non- smoking blacks.
The smoking black low birth weight rate was 0.1918 and their non-smoking black rate which
was 0.1270.
SMOKERS AND THE SMOKING CESSATION CLASS:
One of the services provided by Healthy Start is a smoking cessation class for pregnant
women who smoke. The following analysis examines the differences between the low birth
weight rates for women who had the class versus those who did not.
For all women who smoked compared to all women who smoked and attended the smoking
cessation class, the low birth weight rates were 0.1256 and 0.0840 respectively (bottom
half of Table 1). Here, the relationship between the class and the lower birth weight
rates is averaged for all races and is statistically significant. However, to further
understand association of the smoking cessation class and lower weight birth rates, we
have to look at the two race categories separately.
For non-black women who smoke and did not take the smoking cessation class their rate
was 0.1134 compared to those that did take the class whose rate was 0.0845. For these two
group comparisons there is a noticeable decline in their rates, but these differences are
not statistically significant. Therefore we cannot assume that there is a significant
difference in the low birth weight rates for these groups of women since these differences
could be random fluctuation.
This difference for black smokers, however, is remarkable and statistically
significant. The low birth weight rate for black women who smoked and did not take the
class was 0.1969. For those who did take the class, the rate was 0.0789, a rate less than
half the rate of those who did not take the class. Black women who smoked and took the
class have about the same low birth weight rate as black women who reported not smoking.
Comparing the rate of black smokers who took the class versus black women who do not
smoke is interesting but misleading. It appears that black women who smoke and took the
class have a lower low birth weight rate that those who do not smoke. However, this
difference is not statistically significant. Therefore, there is no relevant difference
between the rates for blacks who do not smoke and those who smoke and have taken the
class. (A Z-score was calculated between the low birth weight rate of black smokers who
took the smoking cessation class and the rate of black women who did not smoke; the
Z-score was not statistically significant.)
SUMMARY
In general, the data in this analysis show that women who smoke and also attend a
smoking cessation class have better low birth weight rates compared to women who smoke and
do not attend the class. In other words, smoking cessation class attendance is associated
with improved low birth weight rates. The rates also show more improvement for black
smokers compared to non-black smokers.
These data are consistent with the theory that smoking cessation classes lead to
decreased smoking and better birth weights. But, the data are also consistent with the
theory that women who attend smoking cessation classes are more willing and able to change
other behaviors and circumstances that affect the birth weight of the infant. A more
extensive analysis would be necessary to separate the effects of the smoking cessation
class from the other factors.
Table 1:
Total Births, Low Birth Weight Births (birth weight less than 2500 grams), and Low
Birth Weight Rates by Race Comparing Non-Smoking, and Smoking Women and the Difference
Associated with Smoking Women that had the Smoking Cessation Class.
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Non-Smokers Smokers
LBW LBW Z Score
Births Births Rate Births Births Rate Diff. in
Rates
All Women 22029 2233 0.1014 6240 766 0.1228 -4.6247***
Non-Black 10065 713 0.0708 5359 597 0.1114 -8.1105***
Black 11964 1520 0.1270 881 169 0.1918 -4.7596***
Smokers without Class Smokers with Class
LBW LBW Z Score
Births Births Rate Births Births Rate Diff. in
Rates
All Women 5835 732 0.1256 405 34 0.0840 2.8844**
Non-Blacks 4992 566 0.1134 367 31 0.0845 1.9029
Blacks 843 166 0.1969 38 3 0.0789 2.5736**
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Z score statistical significance for the difference between two rates is noted by
**p>.05; ***p>.001.
