Options and limitations in studies of successive pregnancy outcomes: an overview

Perinatal stress and food allergy: a preliminary study on maternal reports

Maternal stress in fetal and early life has been associated with the development of respiratory allergies, but no studies exist about food allergy. Stressful events and the quality of caregiving provided, as they affect the emotional and physiologic regulation of the infant, could alter the hypothalamic-pituitary-adrenal and immune system, facilitating an increased allergic response. This study aimed to investigate the influence of perinatal stress, as perceived by mothers, on developing food allergy in childhood. A survey on pregnancy and the first three months after giving birth was submitted to 59 Italian mothers of at least one child suffering from severe food allergy and one completely healthy child, for a total of 118 children examined. The presence of stressful events and the quality of perinatal period for each child were assessed retrospectively. The food allergic children's data were compared to siblings' data through inferential statistics. The results showed a significantly higher number of stressful events occurred during patients' perinatal period, compared to siblings, in particular bereavements in pregnancy and parenting difficulties in postpartum. Mothers reported harder pregnancies and more stressful, harder, and, in general, worse postpartum when referring to their food-allergic children, in comparison with their siblings (p < .05). Psychological aspects are demonstrated to be involved in the development of allergic diseases. This study constitutes the first step to examine the role of early stress and perinatal psychosocial factors in the pathogenesis of food allergy; further studies are necessary to understand individual psychological impact and its relations with genetic and biological factors.

Body size and time-to-pregnancy in black women

STUDY QUESTION

Are overall and central obesity associated with reduced fecundability in US black women?

SUMMARY ANSWER

Overall and central obesity--based on self-reported measures of body mass index (BMI, kg/m(2)), waist circumference and waist-to-hip ratio--were independent risk factors for subfertility in our cohort.

WHAT IS KNOWN ALREADY

Overall obesity (BMI ≥ 30 kg/m(2)) has been associated with infertility in several studies. The role of central obesity is less clear. There are no previous studies of time-to-pregnancy (TTP) in black women.

STUDY DESIGN, SIZE, DURATION

Data were derived from the Black Women's Health Study, a prospective cohort study. During 1995-2011, there were 2239 planned pregnancy attempts reported by 1697 women, resulting in 2022 births. Cohort retention was greater than 80%.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Eligible women were aged 21-40 years and reported at least one planned pregnancy attempt during 1995-2011. Height and weight were reported in 1995, with weight updated every two years; waist and hip circumferences were reported in 1995 and updated in 2003. A validation study within the cohort showed high correlations between self-reported and technician-measured weight (r = 0.97), height (r = 0.93), waist circumference (r = 0.75) and hip circumference (r = 0.74). In 2011, TTP was reported in months. Proportional probabilities regression models were used to estimate fecundability ratios (FRs) and 95% confidence intervals (CI), adjusting for covariates.

MAIN RESULTS AND THE ROLE OF CHANCE

High BMI was associated with delayed conception: relative to BMI 18.5-24.9, FRs for BMI categories of <18.5, 25.0-29.9, 30.0-34.9 and ≥ 35.0 were 0.92 (CI: 0.64-1.32), 0.93 (CI: 0.84-1.03), 0.92 (CI: 0.79-1.06) and 0.73 (CI: 0.61-0.87), respectively. Associations were stronger among nulliparous women (P-interaction = 0.003). After controlling for BMI, reduced fecundability was observed among women with large waist circumferences (≥ 33 versus <26 inches: FR = 0.73, CI: 0.60-0.88) and large waist-to-hip ratios (≥ 0.85 versus <0.71: FR = 0.83, CI: 0.71-0.97).

LIMITATIONS, REASONS FOR CAUTION

TTP was reported retrospectively and error in recall is likely, particularly as time since the pregnancy increases. However, results were similar when based on the most recent versus first pregnancies. Confounding may have been introduced by the lack of control for important determinants of TTP. Nevertheless, control for maternal age and education, which are highly correlated with TTP determinants such as paternal age and persistence in trying, should reduce the extent of confounding. The analysis was confined to planned pregnancies. If pregnancy intention was related both to body size and fecundability, our results could be biased. Bias is likely to be small because we found little difference in body size and other measured characteristics between pregnancy planners and non-planners.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings add to the growing body of literature showing that excess BMI is associated with reduced fecundability and further suggest that central obesity is an important independent risk factor for infertility. The relation of obesity to infertility is especially relevant to US black women because they have higher rates of obesity and infertility. Reductions in overall and central obesity may offer the potential to improve fertility outcomes.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by National Cancer Institute grant CA58420. We have no competing interests to report.

Role of IgG antibodies in association with placental function and immunologic diseases in human pregnancy

During human pregnancy, the maternal immune system develops and changes, providing protection for the growing placenta and fetus. These protective changes provide mechanisms allowing two genetically different individuals to interact with each other without allograft rejection. In addition to normal pregnancy, some pregnancies may develop under immunologic diseases, during which specific monitoring and medical treatments are essential. The aim of this current review is to provide information regarding the development of human placental function during pregnancy, the immunology of human pregnancy and the role of the placenta in providing the fetal tissue with antibodies (IgG and its subclasses 1-4), which are required for the passive immunization of the newborn. In addition, the available methods for the determination of placental function will be explored. Furthermore, immunologic diseases observed during pregnancy and the possible therapies for these diseases will be assessed.

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.

Preterm delivery and risk of subsequent cardiovascular morbidity and type-II diabetes in the mother

OBJECTIVE

Preterm delivery has been shown to be associated with subsequent maternal cardiovascular morbidity. However, the impact of the severity and recurrence of preterm delivery on the risk of specific cardiovascular events and the metabolic syndrome in the mother, have not been investigated.

DESIGN

National registry-based retrospective cohort study.

SETTING

Women delivering in Denmark from 1978 to 2007.

POPULATION

Women with a first singleton delivery (n = 782 287), and with a first and second singleton delivery (n = 536 419).

METHODS

Cox proportional hazard models, with the gestational age stratified into four groups as primary exposure. We made adjustments for maternal age, year of delivery, hypertensive pregnancy disorders, fetal growth deviation, placental abruption and stillbirth.

MAIN OUTCOME MEASURES

Subsequent maternal hypertension, ischaemic heart diseases, thromboembolism and type-II diabetes.

RESULTS

After a first delivery at 32-36 completed weeks of gestation, the adjusted risk of subsequent type-II diabetes increased 1.89-fold (1.69-2.10) and the risk of thromboembolism increased 1.42-fold (1.24-1.62). Women having a preterm delivery in the first pregnancy and a term delivery in the second had a 1.58-fold (1.34-1.86) increased risk of type-II diabetes and a 1.18-fold (0.96-1.44) increased risk of thromboembolism. Women having two preterm deliveries had a 2.30-fold (1.71-3.10) increased risk of type-II diabetes and a 1.80-fold (1.29-2.50) increased risk of thromboembolism.

CONCLUSIONS

Preterm delivery is independent of other pregnancy complications associated with subsequent maternal overt type-II diabetes and thromboembolism. The recurrence of preterm delivery will augment these risks.

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.