Differing prevalence of microcephaly and macrocephaly in male and female fetuses

Prenatal Exome Sequencing for Fetal Macrocephaly: A Large Prospective Observational Cohort Study

OBJECTIVE

To assess the diagnostic utility of exome sequencing (ES) in macrocephalic fetuses.

METHODS

Fetuses with macrocephaly (head circumference (HC) ≥ +2 SD) and negative chromosomal microarray results were included, who had available trio-ES data. Molecular diagnoses were systematically analyzed. Subgroup analyses were performed on the ES diagnostic yield based on gestational age, HC Z-scores, associated anomalies, and growth parameters.

RESULTS

Molecular diagnoses were established in 34 out of 87 macrocephalic fetuses (39.1%) through trio-ES. These diagnoses revealed that the variants predominantly affect key signaling pathways, including mTOR, RASopathies and Sotos syndrome. The detection rate was significantly higher in non-isolated compared to isolated macrocephaly cases (65.0%, 26/40 vs. 17.0%, 8/47; p < 0.001). The most frequent anomalies associated with genetic diagnoses included micromelia (100.0%, 14/14), megalencephaly (100.0%, 2/2), and ventriculomegaly (60.0%, 6/10). Subgroup analysis identified higher diagnostic yields in fetuses diagnosed before 32 gestational weeks, with HC Z-scores ≥ +3 SD, micromelia, and absence of large-for-gestational-age (LGA).

CONCLUSIONS

Exome sequencing significantly enhances the detection of monogenic disorders in macrocephalic fetuses compared with CMA, irrespective of isolated or non-isolated cases. These clinical features and phenotypes are essential for assessing monogenic disorders and for prenatal counseling and evaluations of macrocephalic fetuses.

Epidemiology of Macrocephaly in the Texas Birth Defects Registry, 1999-2019

BACKGROUND

Macrocephaly is a clinical observation denoted as an occipitofrontal head circumference exceeding two standard deviations above same age and sex norms. By its definition, macrocephaly occurs in approximately 3% of the population. Descriptive epidemiologic evaluations of macrocephaly are lacking in the literature. The primary objective of this study was to describe the prevalence of macrocephaly captured by the Texas Birth Defects Registry (TBDR) by infant sex, rural/urban residence, and select maternal characteristics.

METHODS

Cases of TBDR between 1999 and 2019 with a six-digit Centers for Disease Control modified-British Pediatric Association (BPA) code of 742.400 (enlarged brain/head, large head, macrocephaly, megalencephaly) were identified. All pregnancy outcomes and diagnostic certainties were included. Prevalence (per 10,000 live births) and 95% confidence intervals (CIs) were calculated using a Poisson table by rural/urban residence, infant sex, maternal age, education, race/ethnicity, history of diabetes, and body mass index (BMI). Prevalence calculations were repeated across multiple sensitivity analyses including (1) definite, isolated cases excluding those with indication of being either "benign" or "familial", (2) definite, non-isolated cases, (3) definite non-isolated cases excluding chromosomal and syndromic cases, and (4) definite, proportionate (at birth) cases. A secondary objective was to describe the most common co-occurring congenital defects among definite, non-isolated cases.

RESULTS

Overall, between 1999 and 2019, 14,637 cases of macrocephaly were identified in the TBDR resulting in a prevalence of 18.12/10,000 live births (95% CI: 17.83-18.42). Most cases were live born (99%), had a definite diagnosis (87%), and were non-isolated (57%). Prevalence was significantly higher among males, among those with an urban residence, and among mothers who were older, Non-Hispanic White, who had greater than high school education, who had a history of diabetes, and who were obese. Prevalence patterns remained consistent across all sensitivity analyses. The most common co-occurring congenital defects among definite, non-isolated cases were minor and primarily included skull and facial bone anomalies (e.g., plagiocephaly [18%]).

CONCLUSIONS

To our knowledge, this is the first epidemiologic evaluation of macrocephaly in a birth defects registry. The long-term clinical impact of isolated macrocephaly is not well understood and should be the focus of future investigations.

Small size, big problems: insights and difficulties in prenatal diagnosis of fetal microcephaly

Microcephaly is a sign, not a diagnosis. Its incidence varies widely due to the differences in the definition and the population being studied. It is strongly related to neurodevelopmental disorders. Differences in definitions and measurement techniques between fetuses and newborns pose a great challenge for the diagnosis and prognostication of fetal microcephaly. A false positive diagnosis can result (in countries where it is legal) in erroneous termination of pregnancy, where a false negative diagnosis might lead to the birth of a microcephalic newborn. Microcephaly in growth restricted fetuses deserves special attention and separate evaluation as it is an important prognostic factor, and not necessarily part of the general growth retardation. Several genetic syndromes incorporating microcephaly and intrauterine growth retardation (IUGR) are discussed. Deceleration of the head circumference (HC) growth rate even when the HC is still within normal limits might be the only clue for developing microcephaly and should be considered during fetal head growth follow up. Combining additional parameters such as a positive family history, associated anomalies, and new measurement parameters can improve prediction in about 50% of cases, and thus should be part of the prenatal workup. Advances in imaging modalities and in prenatal genetic investigation along with the emergence of new growth charts can also improve diagnostic accuracy. In this article, we review the different definitions and etiologies of fetal microcephaly, discuss difficulties in diagnosis, investigate the reasons for the low yield of prenatal diagnosis, and provide improvement suggestions. Finally, we suggest an updated algorithm that will aid in the diagnosis and management of fetal microcephaly.

Impact of increased paternal age on neonatal outcomes in very-low-birth-weight infants

OBJECTIVE

Despite the trend of increasing paternal age, its impact on neonatal outcomes, particularly in preterm infants, has not been thoroughly investigated. We aimed to evaluate the perinatal characteristics and neonatal outcomes associated with paternal age.

METHODS

Electronic medical records of very low-birthweight infants admitted to our unit from July 2013 to March 2022 were reviewed. Infants grouped according to paternal age (<35 years, 35-39 years, and ≥40 years) were analyzed for differences in perinatal findings and neonatal outcomes.

RESULTS

A total of 637 infants were included (194, 294, and 149 in the <35, 35-39, and ≥40 years groups, respectively). The increase in paternal age paralleled the increase in maternal age. The Z-score of head circumference at birth was significantly different between the groups, showing the lowest median value in the ≥40 years group. Small-for-gestational age (Odds ratio 71.074, p < .001, 95% confidence interval 19.337 - 261.236) and male sex (Odds ratio 3.309, p < .034, 95% confidence interval 1.089 - 8.425), but not paternal or maternal age groups were significant factors associated with head circumference Z-scores less than -2 standard deviation based on the multivariable logistic regression analysis. Infants affected by chromosomal or genetic anomaly were more frequently identified (3.4 vs 0.0 vs 0.5%) in the ≥40 years group than in the other two groups. When infants with anomalies or critical illnesses were excluded, overall neonatal outcomes did not statistically differ according to paternal age.

CONCLUSION

Although increased paternal age ≥40 years may be associated with relatively smaller head circumferences, the impact on fetal head growth does not imply a definite risk for microcephaly. Nonetheless, based on the possible negative impact on chromosomal/genetic anomaly, increased paternal age warrants attention, even though neonatal outcomes concerning prematurity were not significantly affected. A large-scale longitudinal study is needed to further elucidate the impact of advanced paternal age in preterm infants and provide guidelines for appropriate antenatal counseling and surveillance.