Early Puberty in Girls: Danish Study Traces Growth Clues Back to the Infant Years

The research drew on Denmark’s national health registries, linking birth records, routine childhood height and weight measurements, hospital diagnoses and family background information.

A girl's growth chart may hold clues about early development years before a family notices physical changes, according to Danish research that traced body mass index from birth through childhood. The study, 'Distinct body mass index trajectories throughout childhood in girls with early puberty,' published in npj Pediatric Research, identified three growth patterns among girls diagnosed with precocious puberty or premature adrenarche.

Researchers led by Grith Laerkholm found that higher BMI, rapid weight gain in infancy and an unusually early rise in childhood BMI appeared in different combinations, showing that girls with early development do not all follow the same growth path.

Following Growth From Birth to Age Ten

The research drew on Denmark's national health registries, linking birth records, routine childhood height and weight measurements, hospital diagnoses and family background information. The final analysis included 1,874 girls with precocious puberty and 725 with premature adrenarche, selected from 11,068 girls with relevant diagnoses because they met the study's age and measurement requirements. Each girl had a median of 10 BMI measurements, giving researchers a fuller picture than a single weight check could provide.

Precocious puberty refers to pubertal development beginning unusually early; premature adrenarche involves early adrenal hormone activity and related physical changes, which is distinct from the activation of full puberty. Both conditions involve symptoms before age eight in girls. The researchers included diagnoses made between ages four and nine to allow for delays between the first symptoms and medical assessment, excluding younger children to reduce the inclusion of temporary breast development in infancy. The median age at diagnosis was 7.9 years for precocious puberty and 7.5 years for premature adrenarche.

Using a statistical method that groups children with similar growth curves, the team examined BMI patterns from birth to age ten separately for each condition and compared them with World Health Organization growth standards. Across both populations, average BMI stayed in the upper normal range during early childhood before entering the overweight range at approximately seven years. These averages describe groups, rather than the experience of every girl in the study.

Three Different Paths Through Childhood

One important feature was the timing of "adiposity rebound," the point when BMI begins rising again after its usual decline in early childhood. This generally occurs around ages five to seven; an earlier rebound has been associated in previous research with a greater likelihood of later overweight and obesity. In this study, the overall rebound occurred at approximately 4.5 years among girls with precocious puberty and three years among those with premature adrenarche, with some subgroups showing a rise much sooner.

Among girls with precocious puberty, the largest group, labelled "high normal," accounted for 52.6% and had an average BMI near the upper end of the normal range in infancy and early childhood, reaching the overweight range from about age eight. The "early rebound" group represented 38.2%, beginning with BMI within normal limits before a sharper rise from around 3.5 years. The remaining 9.2%, described as "high peak," started with low BMI at birth, gained rapidly during the first year and maintained an average BMI in the overweight range through childhood.

Girls with premature adrenarche showed comparable patterns with some differences in timing. About 46.1% belonged to the "high normal" group, whose average BMI remained near the upper boundary of normal throughout childhood. Nearly 47% followed an "early rebound" pattern, with BMI beginning to climb from approximately age two. The "high peak" group accounted for 7.2%, combining low initial BMI, a pronounced infancy peak and another rise from around 2.5 years, followed by an overweight trajectory.

Birth Size and Family Factors Add Context

Girls in the "high peak" groups generally weighed less at birth, gained weight quickly during infancy and had higher BMI when diagnosed. More of them were born prematurely, including about 18% of those with precocious puberty and 35% of those with premature adrenarche. Girls in the precocious puberty "early rebound" group tended to be heavier at birth, showing that children can reach a higher BMI through different growth patterns. The premature adrenarche "high normal" group also included more girls born early or smaller than expected for the length of the pregnancy.

Mothers of girls in the precocious puberty "high peak" group had the highest average BMI before pregnancy. A similar pattern appeared in the premature adrenarche group, but the evidence was not strong enough to rule out chance. The two groups also had small differences in mothers' smoking habits, education, family income and background. These findings do not prove that a mother's weight or family circumstances caused a child's early development.

The researchers suggest that body fat, hormones, genes and how the body responds to insulin may help explain the connection between growth and early puberty. Babies born smaller who gain weight quickly may be part of this pattern, but the study did not directly test these explanations. Researchers had no information about infant feeding, so they could not assess whether breastfeeding, formula feeding or early diet influenced the girls' growth patterns.

What the Findings Can and Cannot Tell Us

The study used nationwide health records and repeated height and weight measurements, helping researchers spot growth differences from infancy. BMI cannot show exactly how much body fat a child has, and it changes as children grow and enter puberty. Some increases could reflect earlier physical development, although higher BMI was already present before puberty began.

Medical records can contain mistakes, and telling breast tissue apart from body fat in young girls can be difficult. Many girls could not be included because their growth measurements were missing. Researchers also did not compare the girls with a separate group whose puberty began at the usual age, and they could not fully assess the effects of diet, genes or daily habits.

The findings suggest that following growth over several years provides more information than a single BMI measurement. They do not prove that weight gain causes early puberty, that a growth pattern can predict it, or that changing a child's weight would prevent it. The three patterns offer clues for future research into how early growth and puberty are connected.