Background and objectives. Growth curves require regular updates due to secular trends in linear growth. We constructed contemporary growth curves, assessed secular trends in height, and defined body mass index (BMI) cut-off points for thinness, overweight, and obesity in Finnish children. Material and methods: Mixed cross-sectional/longitudinal data of 73,659 healthy subjects aged 0–20 years (born 1983–2008) were collected from providers in the primary health care setting. Growth references for length/height-for-age, weight-for-length/height, and BMI-for-age were fitted using generalized additive models for location, scale, and shape (GAMLSS). BMI percentile curves passing through BMIs 30, 25, 18.5, 17, and 16 kg/m² at the age of 18 years were calculated to define limits for obesity, overweight, and various grades of thinness. Results. Increased length/height-for-age was seen in virtually all age-groups when compared to previous Finnish growth data from 1959 to 1971. Adult height was increased by 1.9 cm in girls and 1.8 cm in boys. The largest increases were seen during the peripubertal years: up to 2.8 cm in girls and 5.6 cm in boys. Median weight-for-length/height had not increased. Conclusions. New Finnish references for length/height-for-age, weight-for-length/height, and BMI-for-age were constructed and should be implemented to monitor growth of children in Finland.

The hypothalamic-pituitary-gonadal (HPG) axis is active in the midgestational foetus but silenced towards term because of the negative feedback effects mediated by the placental hormones. This restraint is removed at birth, leading to reactivation of the axis and an increase in gonadotrophin levels. Gonadotrophin levels are high during the first 3 months of life but decrease towards the age of 6 months except for FSH levels in girls that remain elevated until 3-4 years of age. After this, the HPG axis remains quiescent until puberty. The postnatal gonadotrophin surge results in gonadal activation in both sexes. In boys, testosterone levels rise to a peak at 1-3 months of age and then decline following LH levels. Postnatal HPG axis activation is associated with penile and testicular growth and therefore considered important for the development of male genitalia. In girls, elevated gonadotrophin levels result in the maturation of ovarian follicles and in an increase in oestradiol levels. Biological significance and possible long-term consequences of this minipuberty remain elusive, as do the mechanisms that silence the HPG axis until puberty. However, the first months of life provide a ‘window of opportunity' for functional studies of the HPG axis prior to pubertal development.

OBJECTIVE: Antibiotics have direct effects on the human intestinal microbiota, particularly in infancy. Antibacterial agents promote growth in farm animals by unknown mechanisms, but little is known about their effects on human weight gain. Our aim was to evaluate the impact of antibiotic exposure during infancy on weight and height in healthy Finnish children. METHODS: The population-based cohort comprised 6114 healthy boys and 5948 healthy girls having primary care weight and height measurements and drug purchase data from birth to 24 months. BMI and height, expressed as z-scores at the median age of 24 months (interquartile range 24 to 26 months), were compared between children exposed and unexposed to antibiotics using analysis of covariance with perinatal factors as covariates. RESULTS: Exposed children were on average heavier than unexposed children (adjusted BMI-for-age z-score difference in boys 0.13 SD [95% confidence interval 0.07 to 0.19, P < .001] and in girls 0.07 SD [0.01 to 0.13, P < .05]). The effect was most pronounced after exposure to macrolides before 6 months of age (boys 0.28 [0.11 to 0.46]; girls 0.23 [0.04 to 0.42]) or >1 exposure (boys 0.20 [0.10 to 0.30]; girls 0.13 [0.03 to 0.22]). CONCLUSIONS: Antibiotic exposure before 6 months of age, or repeatedly during infancy, was associated with increased body mass in healthy children. Such effects may play a role in the worldwide childhood obesity epidemic and highlight the importance of judicious use of antibiotics during infancy, favoring narrow-spectrum antibiotics.

Background and objectives. Birth size curves are needed for clinical and epidemiological purposes. We constructed birth weight (BW), length (BL), and head circumference (BHC) references, assessed effects of twinness and parity, and defined cut-off points for small, appropriate, and large for gestational age. Materials and methods. Birth register data of all 753,036 infants born in 1996–2008 in Finland were cleaned to create references reflecting optimal intrauterine growth. The final data included 533,666 singletons and 15,033 twins (median gestation weeks (gws) 40.0 and 37.1, respectively, 41.6% primiparous). Sex-specific BW, BL, and BHC references were constructed from 23 to 43 gws separately for singletons and twins born to primiparous or multiparous mothers. GAMLSS method was used for modelling. Results. In singletons from 36 gws onwards, increased BW and BL were observed in comparison to previous reference from 1979–1983. Twins diverged from singletons from 30 gws onwards. At 37.0 gws, mean BW was 400 g lower and mean BL 1.2 cm shorter than in singletons. From 30 gws onwards, birth size was larger in infants of multiparous than primiparous mothers. Conclusions. Population-based birth size references are available for the evaluation of birth size. Accounting for plurality and parity improves the accuracy of birth size evaluation.

Postnatal pituitary-testicular activation in infant boys is well characterized. However, the ovarian response to pituitary activation in infancy is less well understood. The aim of the study was to compare postnatal developmental changes in the pituitary-ovarian axis in preterm and term infant girls. Sixty-three infant girls, divided into three groups according to gestational age (GA) [i.e. full term (FT; n = 29; GA, 37-42 wk), near term (NT; n = 17; GA, 34-37 wk), and preterm (PT; n = 17; GA, 24-34 wk)] were examined monthly from 1 wk (D7) to 6 months (M1-M6) of age and reexamined at the corrected age of 14 months (cM14). We performed a longitudinal follow-up of urinary FSH and serum anti-Müllerian hormone (AMH) levels and the number of follicles in transabdominal ovarian ultrasonography. The postnatal FSH surge was stronger and more prolonged in NT and PT girls than in FT girls (P ≤ 0.001). Increased folliculogenesis and a rise in AMH levels were observed in all three groups after the FSH surge. In NT and PT girls, follicular development was delayed in comparison with FT girls, and a decrease in high FSH levels around the 40th postmenstrual week was temporally associated with the appearance of antral follicles in ultrasonography and an increase in AMH levels. The postnatal FSH surge results in transient ovarian stimulation in term and preterm girls. A delay in ovarian folliculogenesis shown in ovarian ultrasonography and by low serum AMH levels may provide an explanation for the exaggerated FSH surge in NT and PT girls.

Transient activation of the hypothalamic-pituitary-gonadal (HPG) axis is observed in boys during the first months of life. Previous research suggests increased HPG axis activation in premature infants, but the physiological significance of this has not been studied. The objective of this study was to evaluate the differences in reproductive hormone levels and their biological effects between full-term (FT) and preterm (PT) infant boys. Twenty-five FT and 25 PT (gestational age 24.7-36.6 wk) boys were recruited at birth and followed up monthly from 1 wk to 6 months of age (d 7, months 1-6). Nineteen FT and 20 PT boys were reexamined at 14 months of age. Urinary gonadotropins and testosterone were measured in serial urine samples and compared with testicular and penile growth. Urinary prostate-specific antigen was measured as an androgen biomarker. LH and testosterone levels were higher in PT boys (P < 0.001 for both) than FT boys. Compared with FT boys, FSH levels were lower at d 7 (P = 0.002) but higher from month 1 to month 3 (P = 0.002-0.030) in PT boys. This was associated with significantly faster testicular and penile growth in PT boys compared with FT boys. Transient increase in the prostate-specific antigen levels in both groups indicated androgen action in the prostate. Postnatal HPG axis activation in infancy is increased in PT boys and associated with faster testicular and penile growth compared with FT boys. Possible long-term consequences of hyperandrogenism in PT infant boys warrant further research.