Size at birth, infant growth, and age at pubertal development in boys and girls

Figures & data

Figure 1 Flowchart of the study population after invitation to participate in the Puberty Cohort.

Table 1 Baseline characteristics of the children in the Puberty Cohort (N=15,694), Denmark, 2012–2017. Children are categorized as SGA, AGA, or LGA

	Size for gestational age						Missing
	SGA		AGA		LGA
	n	%	n	%	n	%	n	%
Total	2056	13.1	11,702	74.6	1936	12.3
Child characteristics
Sex							0	0.0
Male	1007	49.0	5636	48.2	983	50.8
Gestational age							0	0.0
<37 weeks	220	10.7	718	6.1	164	8.5
≥37 weeks	1836	89.3	10,984	93.9	1772	91.5
Birth weight (SD)^a	2056	2738 (454)	11,702	3543 (440)	1936	4283 (459)	0	0.0
Weight at 5 months (SD)^a	1406	7035 (911)	8179	7738 (929)	1396	8319 (1043)	4713	30.0
Weight at 12 months (SD)^a	1332	9482 (1102)	7749	10,202 (1132)	1325	10,825 (1321)	5288	33.7
Maternal characteristics
Maternal pre-pregnancy BMI							214	1.4
<18.5	207	10.2	797	6.9	42	2.2
18.5–<25	1318	64.8	7251	62.8	1012	53.0
≥25–<30	360	17.7	2412	20.9	508	26.6
30+	149	7.3	1078	9.3	346	18.1
Smoking during first trimester							53	0.3
Nonsmoker	1247	61.0	8466	72.6	1531	79.2
1–<10 cigarettes per day	592	29.0	2560	22.0	340	17.6
≥10 cigarettes per day	205	10.0	639	5.5	61	3.2
Parity							0	0.0
First child	1354	65.9	5903	50.4	653	33.7
Second or later child	702	34.1	5799	49.6	1283	66.3
Maternal age at menarche							121	0.8
Earlier than peers	495	24.3	2940	25.3	546	28.4
Same as peers	1183	58.0	6657	57.3	1072	55.8
Later than peers	362	17.8	2015	17.4	303	15.8
Highest educational class of parents							31	0.2
High-grade professional	453	22.1	2741	23.5	463	23.9
Low-grade professional	605	29.5	3888	33.3	667	34.5
Skilled worker	620	30.2	3155	27.0	535	27.6
Unskilled worker	305	14.9	1596	13.7	234	12.1
Students	47	2.3	232	2.0	31	1.6
Economically inactive	23	1.1	62	0.5	6	0.3

Notes: ^aMean values in gram (SD) presented instead of column %.

Abbreviations: AGA, appropriate-for-gestational age; BMI, body mass index; LGA, large-for-gestational age; SGA, small-for-gestational age.

Figure 2 Adjusted difference (with 95% CI) in reaching pubertal milestones when comparing SGA and LGA boys to boys born AGA.

Notes: Adjusted for parity, maternal age at menarche, maternal pre-pregnancy BMI, maternal smoking during the first trimester, and highest educational class of parents. Exact estimates are provided in Table S1.
Abbreviations: AGA, appropriate-for-gestational age; BMI, body mass index; LGA, large-for-gestational age; SGA, small-for-gestational age.

Figure 3 Adjusted difference (with 95% CI) in reaching pubertal milestones when comparing SGA and LGA girls to girls born AGA.

Notes: Adjusted for parity, maternal age at menarche, maternal pre-pregnancy BMI, maternal smoking during the first trimester, and highest educational class of parents. Exact estimates are provided in Table S1.
Abbreviations: AGA, appropriate-for-gestational age; BMI, body mass index; LGA, large-for-gestational age; SGA, small-for-gestational age.

Table 2 Mean age difference (in months) at attaining pubertal milestone for each 1-unit increase in birth weight Z-score

Pubertal milestone	n^a	Unadjusted age difference	Adjusted age difference (95% CI)^b
Boys
Tanner genital stage 2	6927	−0.4	−0.5 (−0.9–0.0)
Tanner genital stage 3	6927	−0.4	−0.4 (−0.8–0.1)
Tanner genital stage 4	6927	−0.3	−0.3 (−0.8–0.1)
Tanner genital stage 5	6927	−0.6	−0.6 (−1.3–0.0)
Tanner pubic hair stage 2	6931	−0.2	−0.2 (−0.6–0.3)
Tanner pubic hair stage 3	6931	−0.3	−0.2 (−0.6–0.2)
Tanner pubic hair stage 4	6931	0.0	0.0 (−0.4–0.3)
Tanner pubic hair stage 5	6931	−0.2	−0.2 (−0.7–0.3)
Axillary hair	6936	0.4	0.5 (0.0–1.0)
Acne	6936	0.6	0.4 (−0.1–0.8)
Voice break	6742	−0.1	−0.2 (−0.7–0.2)
Adult voice	6742	0.4	0.4 (−0.4–1.1)
First ejaculation	6923	−0.3	−0.3 (−0.7–0.2)
Girls
Tanner breast stage 2	7348	−0.4	−0.2 (−0.8–0.4)
Tanner breast stage 3	7348	0.4	0.6 (0.2–1.0)
Tanner breast stage 4	7348	0.3	0.6 (0.2–1.0)
Tanner breast stage 5	7348	0.2	0.6 (−0.2–1.4)
Tanner pubic hair stage 2	7349	0.7	0.6 (0.3–1.0)
Tanner pubic hair stage 3	7349	0.7	0.8 (0.5–1.2)
Tanner pubic hair stage 4	7349	0.8	0.9 (0.5–1.4)
Tanner pubic hair stage 5	7349	0.8	1.0 (0.4–1.6)
Axillary hair	7354	0.9	0.9 (0.5–1.4)
Acne	7354	1.1	1.0 (0.5–1.5)
Menarche	7346	0.7	0.9 (0.6–1.2)

Notes: ^aNumber of observations in adjusted analyses. Numbers vary since some children did not provide information on all outcome variables. ^bAdjusted for parity, maternal age at menarche, maternal pre-pregnancy BMI, maternal smoking during first trimester, and highest educational class of parents.

Abbreviations: AGA, appropriate-for-gestational age; BMI, body mass index; LGA, large-for-gestational age; n, number; SGA, small-for-gestational age.

Table 3 Mean age difference (in months) at attaining pubertal milestone for each 1-unit increase in Z-score during the periods from 0 to 5 months, 5 to 12 months, and 0 to 12 months

Pubertal milestone	Z-score change 0 to 5 months			Z-score change 5 to 12 months			Z-score change 0 to 12 months
	n^a	Unadjusted age difference	Adjusted age difference (95% CI)^b	n^a	Unadjusted age difference	Adjusted age difference (95% CI)^b	n^a	Unadjusted age difference	Adjusted age difference (95% CI)^b
Boys
Tanner genital stage 2	3871	−0.3	−0.4 (−1.0–0.3)	3399	−1.1	−0.9 (−2.0–0.1)	3580	−0.7	−0.8 (−1.4– −0.1)
Tanner genital stage 3	3871	−0.4	−0.5 (−1.1–0.1)	3399	−1.5	−1.4 (−2.5– −0.4)	3580	−0.7	−0.9 (−1.5– −0.3)
Tanner genital stage 4	3871	−0.3	−0.4 (−1.0–0.2)	3399	−1.4	−1.3 (−2.3– −0.3)	3580	−0.7	−0.7 (−1.3– −0.1)
Tanner genital stage 5	3871	−0.8	−0.8 (−1.7–0.1)	3399	−1.2	−1.3 (−2.8–0.3)	3580	−1.1	−1.0 (−2.0– −0.1)
Tanner pubic hair stage 2	3872	0.0	−0.1 (−0.7–0.5)	3400	−1.0	−0.9 (−1.9–0.1)	3581	−0.6	−0.6 (−1.2–0.0)
Tanner pubic hair stage 3	3872	−0.3	−0.5 (−1.1–0.0)	3400	−1.3	−1.1 (−2.0– −0.2)	3581	−0.8	−0.9 (−1.5– −0.4)
Tanner pubic hair stage 4	3872	−0.4	−0.5 (−1.0–0.1)	3400	−1.1	−0.9 (−1.8–0.0)	3581	−0.8	−0.7 (−1.2– −0.2)
Tanner pubic hair stage 5	3872	−0.9	−1.0 (−1.6– −0.3)	3400	−1.2	−1.1 (−2.2–0.0)	3581	−1.4	−1.4 (−2.1– −0.8)
Axillary Hair	3875	−1.2	−1.3 (−1.9– −0.6)	3403	−1.2	−1.0 (−2.1–0.2)	3584	−1.5	−1.6 (−2.2– −0.9)
Acne	3875	−0.7	−0.7 (−1.3– −0.1)	3403	−1.2	−0.9 (−1.9–0.1)	3584	−1.2	−1.1 (−1.7– −0.4)
Voice Break	3791	−0.3	−0.4 (−1.0–0.2)	3335	−1.4	−1.2 (−2.3– −0.1)	3506	−1.1	−1.1 (−1.7– −0.5)
Adult Voice	3791	−0.6	−0.7 (−1.7–0.3)	3335	−1.1	−0.6 (−2.4–1.2)	3506	−1.0	−1.0 (−2.0–0.1)
First ejaculation	3870	0.2	0.2 (−0.5–0.8)	3398	−0.8	−0.8 (−1.9–0.2)	3579	−0.2	−0.3 (−0.9–0.3)
Girls
Tanner breast stage 2	4198	−0.3	−0.2 (−1.1–0.6)	3755	−1.0	−1.0 (−2.5–0.6)	3969	−0.5	−0.6 (−1.4–0.3)
Tanner breast stage 3	4198	−0.5	−0.5 (−1.1–0.1)	3755	−0.8	−0.9 (−1.8–0.1)	3969	−0.7	−0.8 (−1.3– −0.2)
Tanner breast stage 4	4198	−0.5	−0.6 (−1.2–0.0)	3755	−1.2	−1.4 (−2.4– −0.3)	3969	−0.9	−1.1 (−1.6– −0.5)
Tanner breast stage 5	4198	−0.6	−0.6 (−1.7–0.4)	3755	−1.8	−2.2 (−4.0– −0.3)	3969	−1.0	−1.3 (−2.3– −0.3)
Tanner pubic hair stage 2	4199	−0.6	−0.5 (−0.9–0.0)	3756	−0.9	−0.9 (−1.7– −0.1)	3970	−0.9	−0.8 (−1.3– −0.3)
Tanner pubic hair stage 3	4199	−1.0	−1.0 (−1.5– −0.6)	3756	−1.0	−1.0 (−1.8– −0.3)	3970	−1.2	−1.3 (−1.8– −0.8)
Tanner pubic hair stage 4	4199	−1.0	−1.0 (−1.6– −0.4)	3756	−1.0	−1.1 (−2.1– −0.2)	3970	−1.3	−1.3 (−1.9– −0.8)
Tanner pubic hair stage 5	4199	−1.5	−1.5 (−2.4– −0.7)	3756	−0.1	−0.2 (−1.7–1.3)	3970	−1.5	−1.6 (−2.5– −0.8)
Axillary hair	4202	−1.3	−1.3 (−1.9– −0.6)	3759	−0.9	−0.6 (−1.7–0.5)	3973	−1.7	−1.7 (−2.3– −1.1)
Acne	4202	−0.8	−0.6 (−1.3–0.1)	3759	−1.4	−1.0 (−2.3–0.2)	3973	−1.3	−1.1 (−1.8– −0.4)
Menarche	4198	−0.7	−0.5 (−1.0– −0.1)	3755	−1.6	−1.7 (−2.5– −0.9)	3969	−1.2	−1.2 (−1.7– −0.7)

Notes: ^aNumber of observations in adjusted analyses. Numbers vary due to different numbers of observations with measurements from birth, 5 months, and 12 months. ^bAdjusted for parity, maternal age at menarche, maternal pre-pregnancy BMI, maternal smoking during the first, trimester and highest educational class of parents.

Abbreviations: AGA, appropriate-for-gestational age; BMI, body mass index; LGA, large-for-gestational age; SGA, small-for-gestational age.

Data availability

The dataset analyzed in the study is not publicly available due to national data security legislation on sensitive personal data.