Gender differences in fetal growth and maternal anthropometry: аn analysis of their impact on newborn weight

   Anthropometric and fetometric parameters of the fetus, including birth weight, are closely related to pregnancy outcomes and the health status of the newborn. The maternal preconception body mass index (BMI) significantly influences on intrauterine development; however, differential growth characteristics between male and female fetuses are often overlooked in such analyses. At the same time, the child’s sex may significantly modify growth rates, the distribution of muscle and adipose tissue, as well as the response to external factors.

   Aim of the study was to determine the patterns of the influence of fetal sex on fetometric parameters, including birth weight, taking into account maternal anthropometric characteristics (BMI and height) and regional peculiarities, in order to optimize perinatal care and improve pregnancy outcomes.

   Material and methods. Medical records of 5161 pregnant women treated at the Kirov Regional Clinical Perinatal Center were analyzed. The study considered maternal anthropometric data (body weight, height, preconception BMI) and fetometric data of the newborns (head circumference, abdominal circumference, birth weight). This retrospective study covered the period from 2016 to 2022. Based on predefined inclusion and exclusion criteria, the women were divided into three groups according to their preconception BMI: below normal (< 18.5 kg/m²), normal (18.5–24.9 kg/m²), and elevated (25.0–29.9 kg/m²). Pregnant women with obesity (BMI ≥ 30 kg/m²) were excluded. Additionally, a stratified analysis of the newborns by sex was conducted to assess the influence of fetal sex on intrauterine growth.

   Results. It was found that, overall, male newborns exhibited higher birth weight, head circumference, and shoulder circumference compared to female newborns, regardless of the maternal BMI group. In the underweight group, infants with lower fetometric parameters were more frequently born; however, the differences between males and females persisted even in this category. In the normal BMI group, children of both sexes had optimal mean birth weights (approximately 3300 ± 400 g), yet male newborns more frequently exceeded the median values. In a group of mothers with elevated BMI group (25.0–29.9 kg/m²), the proportion of infants with a birth weight > 4000 g increased, with male newborns showing even higher values. The statistically significant differences in growth rates between the sexes were evident both in the mean birth weight and in the higher proportion of large-for-gestational-age infants among males. Correlation analysis demonstrated that the combination of fetal sex with maternal preconception BMI and height significantly influences the final fetometric parameters.

   Conclusions. In addition to the maternal BMI and height, the newborn’s sex influences on fetometric parameters, including birth weight. Therefore, in perinatal care, in the formulation of dietary recommendations, and in planning the management of pregnancy, it is advisable to consider not only the maternal anthropometry but also the potential differences between male and female fetuses in intrauterine growth patterns.

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