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The NBDPS was a research study. Research involves collecting information in an organized way to answer specific questions about a certain topic. The collected information is then analyzed to answer the questions that were asked. More specifically, the NBDPS was an observational, population-based, case-control study. That’s a mouthful! Let’s take the terms one at a time.

• Observational means that researchers looked at what was already going on. The study did not test medicines or treatments or ask people perform any actions or behaviors. In the NBDPS, interviewers interviewed families and sent out cheek cell kits, and researchers analyzed the information from the interviews and kits.
• Population-based means it looked at all people with a certain health outcome who lived in a certain area. For this study, that area was a state or certain counties. Researchers looked at whether the number of people with a given outcome in the study area changed over time.
• Case-control study means information was collected from both people who have a health issue (cases) and people who do not have the health issue (controls). The controls might also be called the comparison group. In the NBDPS, controls were selected randomly from the birth certificate records of birth hospitals.

What were the components of the study?
The study had two parts: a telephone interview and collection of cheek cells from family members. Interviewers talked to women who had pregnancies or babies affected by birth defects, as well as mothers of babies with no birth defects.

The interviewers asked women about their pregnancy experience and health. There is no way to recreate the many events and exposures that happen during pregnancy—only women could give us this information. After the interview, the study researchers sent small brushes to each family for collection of cheek cells from mothers, fathers, and babies. Cheek cells contain genetic material called DNA, which we used to examine the role that genetic factors play in the development of a baby.