Table 1. Descriptive statistics and differences in pregnancy characteristics by maternal litter size.

	Combined Mean (±SD)	Twin-born F0 Mean (±SD)	Triplet-born F0 Mean (±SD)	P value*	Cohen’s d
F0 birth weight, g	n = 11	n = 4	n = 7	0.08	1.26
	32.15	35.00	30.51
	(4.07)	(3.72)	(3.48)
F0 female littermates, %	n = 14	n = 6	n = 8	0.27	-0.63
	55.95	50.0	60.42
	(16.80)	(0)	(21.71)
F0 age at time of pregnancy, years	n = 59	n = 22	n = 37	0.22	-0.34
	4.37	4.20	4.48
	(0.11)	(0.74)	(0.90)
Pregnancies in study	n = 59	n = 22	n = 37	0.44	-0.21
	2.93	2.73	3.05
	(1.56)	(1.45)	(1.63)
60 d. gestational weight, g	n = 47	n = 19	n = 28	0.63	0.14
	456.79	464.35	451.66
	(87.79)	(104.02)	(76.48)
90 d. gestational weight, g	n = 42	n = 17	n = 25	0.95	0.02
	465.70	466.73	464.99
	(85.21)	(106.14)	(69.95)
120 d. gestational weight, g	n = 43	n = 18	n = 25	0.95	0.06
	512.43	511.50	513.10
	(80.23)	(100.62)	(63.97)
Gestational weight gain, g	n = 33	n = 15	n = 18	0.21	0.45
	64.35	71.40	58.47
	(29.06)	(26.14)	(30.77)
F1 litter size**	n = 47	n = 20	n = 27	0.11	0.43
	2.98	3.2	2.82
	(0.82)	(0.83)	(0.79)
F1 litter weight, g	n = 45	n = 19	n = 26	0.003	0.95
	82.05	94.78	72.74
	(25.40)	(25.87)	(20.98)
F1 average fetal weight, g	n = 46	n = 20	n = 26	0.10	0.54
	27.47	28.80	26.44
	(4.80)	(4.43)	(4.91)
F1 litters lost to spontaneous abortion	n = 59	n = 22	n = 37	0.10	-0.45
	0.20	0.09	0.27
	(0.41)	(0.29)	(0.45)
F1 offspring lost to stillbirth***	n = 24	n = 11	n = 13	0.57	0.22
	0.29	0.36	0.23
	(0.55)	(0.67)	(0.44)
F1 offspring lost to early neonatal death	n = 43	n = 19	n = 24	0.004	-0.95
	1.12	0.63	1.50
	(1.05)	(0.83)	(0.98)

* Independent two-tailed T-test, α≤0.05.

** Term neonates only, excludes aborted fetuses; Number of litters multiplied by litter size = total number of term offspring in study.

*** Observed births only.