Table 1.

Characteristics of the study population at enrollment and their associations with time to pregnancy, pregnancy, and infertility.

Characteristic	Study population ($n=615$) $\text{Mean}\pm \text{SD}$ (range) or $n$ (%)	TTP (months) ($n=615$) Median (IQR)	p-Valuea	Pregnancy ($n=365$) $\text{Mean}\pm \text{SD}$ or $n$ (%)	Infertility ($n=131$) $\text{Mean}\pm \text{SD}$ or $n$ (%)	p-Valueb
Maternal age (years)	$29.78\pm 3.82$ (24.00–44.00)	—	0.023	$29.83\pm 3.08$	$30.17\pm 2.90$	0.271
Prepregnancy BMI (${\mathrm{kg}/\mathrm{m}}^2$)	$21.17\pm 3.07$ (14.45–37.65)	—	0.094	$21.24\pm 2.94$	$20.55\pm 2.40$	0.017
Age at menarche (years)	$13.37\pm 1.59$ (10.00–18.00)	—	0.323	$13.37\pm 1.74$	$13.45\pm 1.30$	0.660
Current smoking
No	453 (73.5)	4.5 (2.0–10.0)	0.035	293 (80.3)	96 (73.3)	0.204
Live with smoker	153 (24.9)	5.5 (2.0–12.0)		68 (18.6)	32 (24.4)
Yes	9 (1.5)	10.0 (6.5–12.0)		4 (1.1)	3 (2.3)
Education
$<\text{Bachelor’s degree}$	117 (19.0)	5 (2.0–9.5)	0.988	62 (17.0)	20 (15.3)	0.650
$\ge \text{Bachelor’s degree}$	498 (81.0)	5 (2.0–10.0)		303 (83.0)	111 (84.7)
Annual household income (CNY)
$<\mathrm{150,000}$	140 (22.8)	4.0 (2.0–10.0)	0.363	84 (23.0)	29 (22.1)	0.496
150,000–300,000	329 (53.5)	4.5 (1.5–10.0)		201 (55.1)	65 (49.6)
$>\mathrm{300,000}$	106 (17.2)	6.0 (2.0–12.0)		59 (16.1)	27 (20.6)
Refused to answer	40 (6.5)	6.0 (2.0–12.0)		21 (5.8)	10 (7.6)
Parity
0	569 (92.5)	5.0 (2.0–10.0)	0.062	334 (91.5)	121 (92.4)	0.759
$\ge 1$	46 (7.5)	4.0 (2.0–7.0)		31 (8.5)	10 (7.6)
Have you found that you could not cope with all the things that you had to do?c
Never or almost never	267 (43.4)	5.0 (2.0–9.0)	0.239	175 (48.0)	43 (32.8)	0.013
Sometimes	333 (54.2)	5.5 (2.0–12.0)		183 (50.1)	84 (64.1)
Fairly often or very often	15 (2.4)	3.0 (1.0–12.0)		7 (1.9)	4 (3.1)
How often have you been able to control irritations in your life?c
Never or almost never	27 (4.4)	4.0 (2.0–8.0)	0.078	17 (4.7)	5 (3.8)	0.023
Sometimes	168 (27.3)	4.0 (1.5–8.0)		104 (28.5)	22 (16.8)
Fairly often or very often	420 (68.3)	5.5 (2.0–12.0)		244 (66.8)	104 (79.4)

Note: —, data not available; BMI, body mass index; IQR, interquartile range; SD, standard deviation; TTP, time to pregnancy.

^ap-Values for difference in time to pregnancy according to characteristics at enrollment; Spearman correlation for continuous variables, rank sum test for categorical variables.

^bp-Values for differences in characteristics at enrollment according to pregnancy or infertile status at the end of follow-up; t test for continuous variables, chi-square test for categorical variables.

^cQuestions from the PSS-10 questionnaire.