Quantification of selection bias in studies of risk factors for birth defects among livebirths

Abstract

Background: Risk factors for birth defects are frequently investigated using data limited to liveborn infants. By conditioning on survival, results of such studies may be distorted by selection bias, also described as "livebirth bias." However, the implications of livebirth bias on risk estimation remain poorly understood. Objectives: We sought to quantify livebirth bias and to investigate the conditions under which it arose. Methods: We used data on 3994 birth defects cases and 11 829 controls enrolled in the National Birth Defects Prevention Study to compare odds ratio (OR) estimates of the relationship between three established risk factors (antiepileptic drug use, smoking, and multifetal pregnancy) and four birth defects (anencephaly, spina bifida,

Association of Improved Periconception Hemoglobin A1c With Pregnancy Outcomes in Women With Diabetes

“… 8 , 25 In the US, however, induced abortion does not appear to bear any substantial influence on the assessment of risk factors for congenital anomalies. 26 The current study did not distinguish the degree of severity of anomalies, including both major and minor malformations, but did include those recognized up to the age of 1 year.…”

<p>Epidemiological Studies on Fetal Loss – Better Data and Research Methods are Needed</p>

“…A more complete registration of miscarriage events in population would reduce missing data and also allow quantitative assessments of potential bias stemming from exposurerelated pregnancy loss. 24…”

“…Sensitivity analyses comparing results using cases among live birth children only can be carried out to estimate whether an exposure-related pregnancy loss selection bias has occurred. 24 There is a time lag from death to expulsion of the fetus, which could make reverse causation a challenging problem. 25 For example, coffee intake is often lower during pregnancy, perhaps induced by oestrogen-introduced nausea.…”

Selection bias in studies of birth defects among livebirths: Much ado about nothing?

“…In a recent issue of Paediatric and Perinatal Epidemiology, 1 Henike and colleagues report on an important study of selection bias in assessing exposure effects on the risk of congenital anomalies when studies are restricted to livebirths. Specifically, they quantify the socalled "livebirth bias."…”

“…In a recent issue of Paediatric and Perinatal Epidemiology , 1 Henike and colleagues report on an important study of selection bias in assessing exposure effects on the risk of congenital anomalies when studies are restricted to livebirths. Specifically, they quantify the so‐called “livebirth bias.” This may occur when an exposure is associated with the diagnosis of a birth defect and at the same time the survival of fetuses with a birth defect (referred to in the paper as probability of livebirth).…”