Table 2.

Geometric means of plasma prolactin by different categories of menstrual and reproductive characteristics among postmenopausal women, the Singapore Chinese Health Study

	n	Geometric meana	p value	% Difference (p value)†
Menopausal type
Natural	403	7.00
Other	39	7.04	0.96	0.4 (0.96)
Age at menopause, year
< 45	40	7.52
45–49	108	6.98
≥ 50	294	6.96	0.5	− 7.4 (0.4)
Age at menarche, year
< 13	51	8.96
13–14	184	6.90
> 14	207	6.70	0.007	− 25.1 (0.001)
Parity
Nulliparous	25	6.78
Parous	417	7.02	0.8	3.5 (0.8)
Number of births
1–2	119	7.18
3–4	182	6.98
≥ 5	116	6.92	0.6	− 3.4 (0.6)
Age at first birth
≤ 20	85	6.84
21–25	155	6.72
26–30	128	7.32
≥ 31	49	7.58	0.2	11.0 (0.3)
Years between menarche and first birth, among parous women, quartiles
< 9.5	168	6.76
9.5–< 10.5	55	6.62
10.5–< 15.5	130	7.04
≥ 15.5	64	8.14	0.049	20.7 (0.02)
Years from menarche to menopause, quartiles
< 34.5	132	7.22
34.5–< 38.5	151	6.46
38.5–< 40.5	112	6.76
≥ 40.5	47	9.20	0.1	27.6 (0.009)

^aGeometric means are adjusted for age at biospecimen collection, time since last meal, and time of specimen collection

Difference of mean prolactin levels among exposure categories was assessed by F statistics obtained from linear regression models

^†% Difference between last versus first listed categories (e.g., other versus natural menopause, ≥ 50 versus < 45 age at menopause)