Cohort Variation in Selection During Pregnancy and Risk of Selected Birth Defects Among Males

Cohort Selection In Utero against Male Twins and Childhood Cancers: A Population-Based Register Study

BACKGROUND

Cancer ranks as the second leading cause of death among children ages 1 to 14 years in the United States. Previous research finds that strong cohort selection in utero against males precedes a reduction in live-born males considered frail. We examine whether such cohort selection in utero may similarly affect the frequency of childhood cancers among male live births.

METHODS

We examined 1,368 childhood cancers among males born in Sweden over 144 months, from January 1990 to December 2001, and followed to age 15 in the Swedish Cancer Registry. We retrieved the count of male twins by birth month from the Swedish Birth Registry. We applied autoregressive, integrated, moving average time-series methods to identify and control for temporal patterns in monthly childhood cancers and to evaluate robustness of results.

RESULTS

Fewer childhood cancers occur among monthly male birth cohorts with elevated selection in utero (i.e., a low count of live-born male twins). This association appears in the concurrent month (coef = 0.04; 95% CI, 0.001-0.079) as well as in the following month in which most births from the twin's conception cohort are "scheduled" to be born (coef = 0.055; 95% CI, 0.017-0.094).

CONCLUSIONS

Elevated cohort selection in utero may reduce the number of frail male gestations that would otherwise have survived to birth and received a cancer diagnosis during childhood.

IMPACT

This novel result warrants further investigation of prenatal exposures, including those at the population level, that may induce cohort selection in utero for some cancer types but not others.

Risk factors of early mortality after neonatal surgery in Tunisia

BACKGROUND

Research concerning factors of death after neonatal surgery is scarce. Insight into mortality might improve perioperative care. This study aimed to identify predictive factors of mortality after neonatal surgery in a low income country (LIC).

METHODS

Charts of all newborn patients who underwent surgical procedures under general anesthesia during the neonatal period in our department of pediatric surgery between January 2010 and December 2017 were reviewed. We used univariate and multivariate analysis to evaluate perioperative variables potentially predictive of early postoperative mortality.

RESULTS

One hundred eighty-two cases were included in the study: 41 newborns (28.6%) were premature (<37 weeks of gestation) and 52 (22.5%) weighed less than 2.5 kg. The most commonly diagnosed conditions were esophageal atresia (24%) and bowel obstruction (19%). Forty-four patients (24%) died during hospitalization. The highest rate of mortality was observed for congenital diaphragmatic hernia. Univariate analysis showed that perinatal predictive variables of mortality were prematurity, low birth weight, the necessity of preoperative intubation, and duration of surgery more than 2 h. Logistic regression showed three independent risk factors, which are the duration of surgery, low birth weight and the necessity of preoperative intubation.

CONCLUSION

The overall mortality in infants undergoing neonatal surgery is still high in LICs. Knowledge of independent risk factors of early mortality may help clinicians to more adequately manage the high-risk population.

TYPE OF THE STUDY

Clinical research paper.

LEVEL OF EVIDENCE

III.

The life-course association of birth-weight genes with self-rated health

This study examines the impact of genes associated with normal-range birth weight (2500-4500 grams) on self-rated health in mid-to-late life course. Fifty-eight previously identified genetic variants that explain the variation in the normal-range birth weight were used to construct a genetic measure of birth weight for the non-Hispanic white sample from the Health and Retirement Study. Our results show that the genetic tendency toward higher birth weight predicts better self-rated health in mid-to-late life course net of various demographic, socioeconomic, and health behavioral factors. We also examine the heterogeneous effects of birth-weight genes across birth cohorts and age groups. Moreover, to clarify the paradox that higher birth weight can predict both better self-rated health and higher BMI, we show the positive association between birth weight genes and BMI can only hold within the normal-range BMI (18 ≤ BMI < 30). Overall, these findings suggest the genetic factors underlying the normal-range birth weight can have life-courseimpacts on health.

A test of oscillation in the human secondary sex ratio

Background and objectives

The sex ratio of human birth cohorts predicts the health and longevity of their members. Most literature invokes natural selection in support of the argument that heritable tendencies to produce male or female offspring induce oscillation in the sex ratio and its sequelae. Tests of the argument remain exceedingly rare because they require vital statistics describing many generations of a population both unaffected by migration and exposed to an exogenous stressor virulent enough to change the sex ratio at birth. We contribute to the literature by using time-series modeling to detect oscillation in the best data currently available for such a test.

Methodology

We apply rigorous time-series methods to data describing Sweden from 1751 through 1830, a period when the population not only aged in place without migration, but also exhibited the effects of an Icelandic volcanic eruption including a historically low secondary sex ratio. That very low sex ratio should have induced oscillation if heritable mechanisms appear in humans.

Results

We detected oscillation in the ratio but not that predicted by heritable tendencies to produce males or females. We found peak-to-trough oscillation at 14 rather than the approximately 32 years expected from the heritable tendencies argument.

Conclusions and implications

Our findings suggest that mechanisms other than perturbation of heritable tendencies to produce males or females induce oscillation in the human secondary sex ratio. These other mechanisms may include reproductive suppression and selection in utero.

LAY SUMMARY

The male to female ratio in human birth cohorts predicts longevity but its variation over time remains unexplained. We test the long-held theory that the ratio oscillates due to heritable tendencies to produce males or females. We find oscillation, but it appears due to social processes rather than heritable mechanisms.

Relation of in-utero exposure to antiepileptic drugs to pregnancy duration and size at birth

BACKGROUND

The associations of individual antiepileptic drugs (AEDs) with pregnancy duration and size at birth, and potential dose relations, are not well characterized.

METHODS

This cohort study used nationwide Swedish register data (1996-2013). Adjusting for smoking, epilepsy and other AED indications, we used linear and quantile regression to explore associations with pregnancy duration, and birth weight, length, and head circumference (the last three operationalized as z-scores). We used logistic regression for preterm delivery, small for gestational age, and microcephaly. Lamotrigine was the reference drug.

RESULTS

6,720 infants were exposed to AEDs in utero; AED exposure increased over the study period. Relative to lamotrigine-exposed infants, carbamazepine-exposed infants were born, on average, 1.3 days earlier (mean [95% confidence interval]: -1.3 [-2.3 to -0.3]); were 0.1 standard deviations (SDs) lighter (-0.1 [-0.2 to 0.0]); and had a head circumference that was 0.2 SDs smaller (-0.2 [-0.3 to -0.1]). Pregabalin-exposed infants were born, on average, 1.1 days earlier (-1.1 [-3.0 to 0.8]); were 0.1 SDs lighter (-0.1 [-0.3 to 0.0]); and had the same head circumference as lamotrigine-exposed infants. Levetiracetam-exposed infants were born, on average, 0.5 days earlier (-0.5 [-2.6 to 1.6]); were 0.1 SDs lighter (-0.1 [-0.3 to 0.0]); and had a head circumference 0.1 SDs smaller (-0.1 [-0.3 to 0.1]). Valproic acid-exposed infants had, on average, the same duration of gestation and birth weight z-score as lamotrigine-exposed infants, but had a head circumference 0.2 SDs smaller (-0.2 [-0.2 to -0.1]). Associations between carbamazepine exposure and pregnancy duration and between valproic acid exposure and pregnancy duration and birth weight z-score were more negative at the left than at the right tails of the outcome distributions. Effect-measure modification and dose-response relations were noted for some of the associations.

CONCLUSIONS

Relative to lamotrigine, valproic acid and carbamazepine were associated with smaller head circumference.

Down syndrome among primiparae at older maternal age: A test of the relaxed filter hypothesis

BACKGROUND

Down syndrome (DS) ranks as one of the most common birth defects in the United States. The relaxed filter hypothesis (RFH) asserts that mothers with no previous children but nearing reproductive senescence reduce fetal selectivity against DS pregnancies in the first trimester given the high probability of having no offspring at all if the DS pregnancy is not carried to term. We test the parity prediction of RFH-specifically, that pregnancies to older mothers with no previous live births show an elevated prevalence of DS above values expected from the separate contributions of older maternal age and primiparity.

METHODS

We retrieved maternal age and parity information on 2,748 DS cases (live, stillborn, or terminated due to anomaly) from the Paris Birth Defects Registry, 1983-2015. We used two waves of the Enquête Fertility Survey (n = 5,460) and counts of stillbirths to calculate total prevalence of DS by maternal age and parity.

RESULTS

Primiparous mothers 35+ years show the greatest prevalence of any parity group (9.78 cases per 1,000 deliveries). Tests for additive interaction of primiparity and older maternal age reject the null (relative excess risk due to interaction = 1.01; 95% confidence interval: 0.33, 1.69; null value on additive scale is 0).

CONCLUSIONS

Relaxed selection may account for 10% of the increase in the prevalence, among older primiparous mothers, of DS detected during or after the 11th week. Future work may hold implications for understanding, among older mothers, the strength of this maternal screen against other defects.

Selection in utero and population health: Theory and typology of research

Public health researchers may assume, based on the fetal origins literature, that "scarring" of birth cohorts describes the population response to modern-day stressors. We contend, based on extensive literature concerned with selection in utero, that this assumption remains questionable. At least a third and likely many more of human conceptions fail to yield a live birth. Those that survive to birth, moreover, do not represent their conception cohort. Increasing data availability has led to an improved understanding of selection in utero and its implications for population health. The literature describing selection in utero, however, receives relatively little attention from social scientists. We aim to draw attention to the rich theoretical and empirical literature on selection in utero by offering a typology that organizes this diverse work along dimensions we think important, if not familiar, to those studying population health. We further use the typology to identify important gaps in the literature. This work should interest social scientists for two reasons. First, phenomena of broad scholarly interest (i.e., social connectivity, bereavement) affect the extent and timing of selection in utero. Second, the life-course health of a cohort depends in part on the strength of such selection. We conclude by identifying new research directions and with a reconciliation of the apparent contradiction between the "fetal origins" literature and that describing selection in utero.