Lesson 4: Scientific Investigation, Excite Curriculum, Folic Acid, NCBDDD, CDC

Estimated Time: 35 minutes

Teachers: Divide the class into small groups and respond to these questions, then have group members report their responses to the class.

Before starting any investigation, it is good to find background facts on the problem.

How could you learn more about birth defects? Where could you go to find more facts on birth defects? Who could you talk to for this information?

Places to learn more could include the internet, encyclopedias, books, and magazines. People to talk to could include a parent who has a child with a birth defect, people with spina bifida, workers from the March of Dimes or a public health department, or doctors and nurses who treat people with spina bifida.

Suppose you are a scientist and you have been told to go to Brownsville, Texas to find out what is causing the cases of anencephaly. What do you need to do before you go? What do you need to bring?

Gather study supplies like a laptop computer, lab equipment, a map and list of places to go, and a notebook. You should also prepare a list of questions to ask the women who have had a baby with the birth defect. You will also have to make reservations for the trip and make a plan for who to meet and what to do once you arrive at the study area.

Step 2) Show that an outbreak exists

RATE. The number of cases in a population during a certain time.

An outbreak occurs when there are more cases of a certain disease than expected. To know if an outbreak exists, we need to know if the number of cases is above what is expected. In the U.S., the rate of NTDs is 1 per 1000 babies. This means that on average for every 1,000 babies born, one is born with an NTD.

About 6,000 babies are born per year in Cameron County. If the rate of neural tube defects in the U.S. is 1 per 1,000 births, how many of the 6,000 babies born in Cameron County in a year would you expect to have an NTD?

In real life, six babies were born with anencephaly in Brownsville within 6 weeks in 1991. If these rates continued, how many babies would you expect to be born with anencephaly in Cameron County in a whole year?

Compare the expected rate from U.S. averages to the projected rate if the rates in Cameron County continued. Do you think this problem should be investigated? Give at least two reasons this problem should be studied.

What is the rate of NTDs in your state? You could check health department reports, birth and death records, and hospital records. Another way to find out would be to check out your State Birth Defects Surveillance System. Go here and open Appendix C to find a state contact. Pages 6-14 list the contacts by state.

A third step is to make sure the cases of anencephaly were true cases. Sometimes laboratories make mistakes or new doctors count cases in a different way. When this happens, it can seem like an outbreak when there really aren't more cases than normal. Anencephaly is easy to notice because it is obvious when a baby doesn't have a skull and part or all of its brain.

Step 4) Define and find all cases

CASE DEFINITION. A way to describe who has the health problem by identifying what happened, where it happened, and when it happened. For example, if several students got sick after eating lunch at school, the case definition would include only those students at that particular school who threw up at least 3 times on May 1st and 2nd. In the NTD study in Cameron County, researchers defined a case as -- anencephaly diagnosed in babies born in Cameron County during 1986-1991.

The researchers wanted to look for NTD cases before 1991 to see if the current rates were higher than normal. First, they needed a case definition. This case definition would help them decide who to study. They decided to include all babies whose NTDs were noted in medical records from 1986 to 1991 in Cameron County. Then they searched records and counted the cases they found.

If you were trying to find all the cases of anencephaly, where would you look for this info? (Hospitals, birth and death certificates, health departments, mothers, laboratories, death records, doctors' files, clinic records, district health record)

Medical records at hospitals, and at a local spina bifida clinic were studied to find the prevalence of NTDs in Cameron County. The rate of NTDs from 1986 until 1989 was 1.5 per 1,000 births. In 1990 and 1991 the rate was 2.7 per 1,000 births. All of these numbers are higher than the national average of 1 case per 1,000 births. Researchers have found that Hispanics have a higher rate of births with an NTD than the general U.S. population, but they do not know why. Because Cameron County has a large Hispanic population, we can expect the rate for Cameron County to be higher than the U.S. rate. In 1990 and 1991, the rate of 2.7/1000 is about three times higher than the average rate in the U.S.

Have the students interpret the graphs (possibly on an overhead) and discuss what they think may have happened.

When these cases occurred in Cameron County in 1991, little was known about the cause of NTDs like anencephaly. It was known that in the United States NTDs are most common among Hispanics and least common among African Americans. The birth defects are also more common in poorer families. Researchers from the CDC wanted to know what was causing the NTDs. If there was a problem that was causing these deaths, they wanted to find it so that they could stop the problem. Community members thought the birth defect problems could be caused by pollution from pesticide use and the growing assembly plant industries along the Mexico/U.S. border. The scientists used all of the information they gathered to make educated guesses (they made hypotheses) and investigated each of these factors (they tested hypotheses). Then, they decided to:

1) Conduct a case control study to define risk factors of the parents of cases and controls
2) Conduct lab testing for nutrition and environmental factors
3) Test air, soil, water, and pesticides

CASE-CONTROL STUDY. An type of retrospective study that uses cases (health problem) and compares them with controls (without the health problem) to find out what may have caused the problem.

Twenty-eight babies who died from anencephaly from 1989 to 1991 were found from the birth and hospital records. The mothers of these babies were called the case mothers. Then 26 mothers who had normal babies born during the same 2 years were chosen. These mothers were called control mothers. Since this type of study looks at a problem that already happened it is called a retrospective study.

Epidemiologists interviewed the mothers of these babies in either English or Spanish. Both the case mothers and control mothers were asked 300 questions about their lives 6 months before pregnancy and during pregnancy. Some of the questions were about where they lived, where they worked, what they ate, how often they visited a doctor, what type of work they did, where they got their drinking water, and if they had air conditioning. The mothers' blood and urine were tested for chemicals that may have been in their bodies and could harm the baby. Drinking water, surface water, air, and soil were tested. Records were checked for past pesticide use (chemical spraying for bugs) near the mothers' homes. The scientists made a map showing where the case mothers and control mothers lived to see if there were any major differences between the two groups.

Click here to see map. Note: this type of map is new for many students. Point out the importance of reading the title and key. The lines are streets, the triangular and circular symbols represent the homes of case mothers and control mothers in the study, and the Rio Grande River at the bottom separates Texas from Mexico. Ask the students what they learned from the map. This was an actual map used by researchers. They found no real difference between the resident areas of case mothers and control mothers.

When all of the interviews were finished and the data were analyzed, no real differences were found between the cases and controls. Mothers of both the normal babies and the babies with the TD lived in similar homes and locations, ate about the same types and amounts of foods, worked in the same types of jobs, received about the same amount of prenatal (before birth) care, etc. Tests of air, soil, water, and for chemicals found that everything was normal. The one thing that they did find was that women who didn't finish high school were more than twice as likely to have a baby with an NTD than women who had graduated.

Discuss possible reasons more mothers who didn't finish high school had babies with NTDs.

Education could make a difference because women who finish high school may have learned more about health and may be older and better prepared for pregnancy. Education could allow people to have better jobs, earn more money, and have better homes, nutrition, and medical care.

1) Women who have already had an affected pregnancy should take folic acid. More research about folic acid should be done.

2) The state needed a more complete system to keep track of all the NTD cases in the state and especially along the border. (In 1993, Texas Department of Health began closely tracking all babies born with NTDs along the border).

3) More studies should be done to look for causes of birth defects in this high-risk area.

After these studies were finished, the scientists still didn't find an exact cause of these birth defects occurring along the border. Some people living in the area think that pollution from factories across the Mexican border may have caused the problem, but there has been no evidence to show that to be the cause. Even with studies going on now we still don't know exactly what caused the increased numbers of these birth defects. Often birth defect clusters are unsolved. Maybe you can think of birth defect clusters that you'd like to solve someday.

Date: September 6, 2006
Content source: National Center on Birth Defects and Developmental Disabilities