Table 1.

Baseline characteristics of the study population

	Pregnancy after breast cancer (n=992)	Non-pregnancy after breast cancer (n=30,769)	p-value	All (n=31,761)
Age at cancer diagnosis (yr)	31.8±4.5	39.6±4.5	< 0.001	39.3±4.7
≤ 35	788 (79.4)	5,722 (18.6)	< 0.001	6,576 (20.5)
36-45	204 (20.6)	25,047 (81.4)		25,355 (79.5)
Age at time of pregnancy (yr) (missing=30,769)	35.4±4.4	-	-	35.4±4.4
< 35	484 (48.8)	-	-	484 (48.8)
≥ 35	508 (51.2)	-		508 (51.2)
Difference between pregnancy age of patients and age at cancer diagnosis (yr)	3.60±2.00	-	-	3.60±2.00
Person year (yr)	5.92±2.33	-		4.92±2.55
Chemotherapy
Yes	318 (32.1)	10,818 (35.2)	0.044	11,136 (35.1)
No	674 (67.9)	19,951 (64.8)		20,625 (64.9)
Radiotherapy
Yes	702 (70.8)	21,044 (68.4)	0.113	21,746 (68.5)
No	290 (29.2)	9,725 (31.6)		10,015 (31.5)
Ovarian preservation (missing=20,625)
Yes	2 (0.2)	128 (0.4)	0.090	130 (0.4)
No	316 (31.9)	10,690 (34.7)		11,006 (34.7)
Trastuzumab therapy
Yes	13 (1.3)	1,058 (3.4)	< 0.001	1,071 (3.4)
No	979 (98.7)	39,711 (96.6)		30,690 (96.6)
Adjuvant hormonal therapy
Yes	366 (36.9)	18,768 (61.0)	< 0.001	19,134 (60.2)
No	626 (63.1)	12,001 (39.0)		12,627 (39.8)
Hormone therapy duration (day)
Mean±SD	1,061.9±709.9	1,241.2±560.6	< 0.001	1,237.8±564.4
Median	1,059	1,355		1,349
Time between surgery and conception (day)
Mean±SD	1,176.4±868.6	-	< 0.001	1,176.4±868.6
Median	1,061	-		1,061
SEER stage (missing=8,936)
Localized	341 (34.4)	11,102 (36.1)	< 0.001	11,443 (36.0)
Regional	183 (18.5)	8,417 (27.4)		8,600 (27.1)
Distant	9 (0.9)	539 (1.75)		548 (1.7)
Unknown	74 (7.5)	2,160 (7.0)		2,234 (7.0)
Missing	385 (38.8)	8,551 (27.8)		8,936 (28.1)

Values are presented as mean±SD or number (%). SD, standard deviation; SEER, Surveillance, Epidemiology, and End Results.