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Editorial
. 2007 Aug 30:7:18.
doi: 10.1186/1471-2393-7-18.

Measuring perinatal complications: methodologic issues related to gestational age

Aaron B Caughey  1
Affiliations
Editorial

Measuring perinatal complications: methodologic issues related to gestational age

Aaron B Caughey. BMC Pregnancy Childbirth. .

Abstract

Background: Perinatal outcomes differ by week of gestational age. However, it appears that how measures to examine these outcomes vary among various studies. The current paper explores how perinatal complications are reported and how they might differ when different denominators, numerators, and comparison groups are utilized.

Conclusion: One issue that can clearly affect absolute rates and trends is how groups of women are categorized by their gestational age. Since most perinatal outcomes can only occur in women and neonates who have delivered, using the number of pregnancies delivered (PD) as the denominator of outcomes is appropriate. However, for an outcome such as antepartum stillbirth, all women who are pregnant at a particular gestational age are at risk. Thus, the denominator should include all ongoing pregnancies (OP). When gestational age is used by week this means using both deliveries during a particular week plus those women who deliver beyond the particular week of gestation in the denominator. Researchers should be careful to make sure they are utilizing the appropriate measure of perinatal complications so they do not report findings that would be misleading to clinicians, patients, and policy makers.

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Figures

Figure 1
Figure 1
Comparing the denominators of pregnancies delivered (PD) and ongoing pregnancies (OP). Pregnancies delivered consists of just those women delivered during a particular week of gestation. Ongoing pregnancies consists of both those women delivered during a particular week plus those pregnancies that progress beyond a particular gestational age.
Figure 2
Figure 2
A – Traditionally, when controlling for gestational age, one compares women induced at a given gestational age to those who experience spontaneous labor at the same gestational age. B – Clinically, we are deciding between induction of labor at the current gestational age versus expectant management leading to delivery at a greater gestational age [24].
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