The analysis of recurrence risk as an epidemiological tool

Maternal Smoking Status in Successive Pregnancies and Risk of Having a Small for Gestational Age Infant

BACKGROUND

Smoking during pregnancy is linked to having a small for gestational age (SGA) baby. We estimated SGA risk among women who smoked persistently, quit smoking or started smoking during their first two pregnancies.

METHODS

Data from the population-based Medical Birth Registry of Norway was used to evaluate self-reported smoking at the beginning and end of two successive pregnancies among 118 355 Nordic women giving birth 1999-2014. Relative risks (RR) with 95% confidence intervals (CI) of SGA in the second pregnancy were estimated using adjusted generalised linear models with non-smokers during both pregnancies serving as referent category.

RESULTS

Daily smokers throughout both pregnancies had almost threefold increased SGA risk in the second pregnancy (RR 2.9, 95% CI 2.7, 3.1). Daily smokers in the first pregnancy, who abstained in the second, had a 1.3-fold increased risk (95% CI 1.1, 1.5). Intermediate risks were found among persistent daily smokers who quit by the end of the second pregnancy (RR 2.0, 95% CI 1.6, 2.4) and non-smokers in first pregnancy who smoked daily throughout their second (RR 1.8, 95% CI 1.4, 2.3). Persistently smoking women without SGA in first pregnancy, had a 2.7-fold increased risk of SGA in second pregnancy (95% CI 2.5, 3.0).

CONCLUSIONS

Smoking throughout two successive pregnancies was associated with the greatest increased SGA risk compared with non-smokers, while cessation before or during the second pregnancy reduced this risk. Women who smoked in the first pregnancy without experiencing SGA are not protected against SGA in second pregnancy if they continue smoking.

Recurrence of perinatal death in Northern Tanzania: a registry based cohort study

Background

Perinatal mortality is known to be high in Sub-Saharan Africa. Some women may carry a particularly high risk which would be reflected in a high recurrence risk. We aim to estimate the recurrence risk of perinatal death using data from a hospital in Northern Tanzania.

Methods

We constructed a cohort study using data from the hospital based KCMC Medical Birth Registry. Women who delivered a singleton for the first time at the hospital between 2000 and 2008 were followed in the registry for subsequent deliveries up to 2010 and 3,909 women were identified with at least one more delivery within the follow-up period. Recurrence risk of perinatal death was estimated in multivariate models analysis while adjusting for confounders and accounting for correlation between births from the same mother.

Results

The recurrence risk of perinatal death for women who had lost a previous baby was 9.1%. This amounted to a relative risk of 3.2 (95% CI: 2.2 - 4.7) compared to the much lower risk of 2.8% for women who had had a surviving baby. Recurrence contributed 21.2% (31/146) of perinatal deaths in subsequent pregnancies. Preeclampsia, placental abruption, placenta previa, induced labor, preterm delivery and low birth weight in a previous delivery with a surviving baby were also associated with increased perinatal mortality in the next pregnancy.

Conclusions

Some women in Tanzanian who suffer a perinatal loss in one pregnancy are at a particularly high risk of also losing the baby of a subsequent pregnancy. Strategies of perinatal death prevention that target pregnant women who are particularly vulnerable or already have experienced a perinatal loss should be considered in future research.

Hospital data reporting on postpartum hemorrhage: under-estimates recurrence and over-estimates the contribution of uterine atony

This study aimed to explore whether recording of a prior adverse pregnancy outcome (postpartum hemorrhage) in a medical record increases the likelihood that recurrence of the same event is reported in hospital data. Using a sample of 588 pregnancies [2 consecutive pregnancies for 294 randomly selected women with at least one postpartum hemorrhage (PPH)], we compared 'coded' recurrence rates in hospital data with those obtained from medical record audit. 'Coded' recurrence in a second pregnancy was also compared for women with or without a documented history of prior PPH. We found a 'coded' recurrence rate of 18.5% and an 'audited' recurrence rate of 28.4%. The 'coded' rate of recurrence among women who had a documented history of PPH was 27.4% compared to 19.1% when the previous PPH was not noted in the second pregnancy medical record. Medical record reporting of uterine atony as the cause for postpartum hemorrhages in first and second births was 37.9 and 34.0% while 'coded' hospital data reporting attributed 79.8 and 73.9% respectively to atony. Our study results indicate that a history of postpartum hemorrhage may be a stronger risk factor for subsequent PPH than previously demonstrated. A recorded history of PPH was associated with an increased likelihood of reporting a subsequent PPH, and in such cases recurrence rates approximate true recurrence. The contribution of uterine atony as a cause of postpartum hemorrhage is over-estimated using hospital data.

U.S. Maternally linked birth records may be biased for Hispanics and other population groups

PURPOSE

We sought to advance understanding of linkage error in U.S. maternally linked datasets and how the error might affect results of studies based on the linked data.

METHODS

North Carolina birth and fetal death records for 1988-1997 were maternally linked (n=1,030,029). The maternal set probability, defined as the probability that all records assigned to the same maternal set do in fact represent events to the same woman, was used to assess differential maternal linkage error across race/ethnic groups.

RESULTS

Maternal set probabilities were lower for records specifying Asian or Hispanic race/ethnicity, suggesting greater maternal linkage error for these sets. The lower probabilities for Hispanics were concentrated in women of Mexican origin who were not born in the United States.

CONCLUSIONS

Differential linkage error may be a source of bias in studies that use U.S. maternally linked datasets to make comparisons between Hispanics and other groups or among Hispanic subgroups. Methods to quantify and adjust for this potential bias are needed.

Cryptorchidism concordance in monozygotic and dizygotic twin brothers, full brothers, and half-brothers

OBJECTIVE

To study concordance rates of cryptorchidism (undescended testis) in pairs of boys with varying family structure, to evaluate the risk contribution from the intrauterine environment and genetic factors.

DESIGN

Population based study of 1,024,500 Danish boys born from January 1, 1973 to December 31, 2004. Classic twin method and computerized square dance design.

SETTING

Hospitals and outpatient clinics.

PATIENT(S)

Six groups of boy pairs: boys with no relation, paternal half-brothers, maternal half-brothers, full brothers, dizygotic twin brothers, and monozygotic twin brothers.

INTERVENTION(S)

Observational study.

MAIN OUTCOME MEASURE(S)

Status on each individual regarding cryptorchidism and orchiopexy from the Danish National Patient Register.

RESULT(S)

Concordance rates of cryptorchidism in the groups were as follows: boys with no relation 3.2% (95% confidence interval 2.7%-3.6%), paternal half-brothers 3.4% (2.3%-4.7%), maternal half-brothers 6.0% (4.5%-7.7%), full brothers 8.8% (8.3%-9.8%), dizygotic twin brothers 24.1% (16.0%-33.6%), and monozygotic twin brothers 27.3% (15.5%-41.2%).

CONCLUSION(S)

The concordance rate was higher in maternal than in paternal half-brothers, and much higher but of equal magnitude in both twin groups. The findings strongly support that the intrauterine environment and maternal inheritance are contributing to the occurrence of cryptorchidism.

Epidemiologic approaches for studying recurrent pregnancy outcomes: challenges and implications for research

The study of recurrence of pregnancy-related complications and outcomes can offer powerful insights to understanding patient-related risks for subsequent pregnancies. Such studies, when designed, analyzed, and interpreted correctly, can help distinguish genetic from environmental causes that portend increased recurrence of a particular pregnancy complication (eg, recurrence of gestational diabetes) or a perinatal outcome (eg, recurrence of preterm birth or preeclampsia). Recurrence risk studies can be challenging in other dimensions, including inherent biases, generalizability of findings, inadequate study size, and inappropriate use of analytic models to study recurrence. Other common misperceptions in studies of recurrence risk are highlighted, including issues with terminology and interpretation of recurrence risks. A review of available epidemiologic study designs is presented and the usefulness and applicability of each design for addressing specific etiologic questions as they relate to recurrence risks are contrasted.