Table 2.

Morphological comparisons of the heaviest and lightest placentas in a litter at days 16 and 19 of pregnancy

	E16 (5 litters)		E19 (8 litters)
	H	L	H	L
Volume of placental compartments (mm3)
Placenta	116.0 ± 2.6	80.4 ± 2.5*	103.7 ± 5.7	76.9 ± 5.8*
Lz	50.0 ± 2.5	44.9 ± 0.9	58.9 ± 1.8†	45.3 ± 3.0*
Jz	42.3 ± 0.9	24.8 ± 0.9*	30.5 ± 4.4	21.1 ± 2.2
Db	23.7 ± 3.1	10.8 ± 1.7*	14.3 ± 1.4	10.4 ± 1.4
Volume of labyrinthine zone components (mm3)
FC	9.7 ± 1.2	5.5 ± 0.5*	12.2 ± 0.9	8.5 ± 1.6*
MBS	10.7 ± 0.7	10.0 ± 0.8	12.9 ± 0.9	11.0 ± 1.1*
LT	29.7 ± 2.7	29.2 ± 0.6	33.0 ± 2.3	25.0 ± 2.0*
Placental compartment volume fraction (%)
Lz	41.1 ± 1.3	48.4 ± 0.7*	49.4 ± 1.6†	50.4 ± 0.4†
Jz	37.2 ± 0.6	33.7 ± 0.7*	32.2 ± 1.6†	31.4 ± 1.1
Db	26.6 ± 1.8	21.1 ± 1.8	21.6 ± 0.9	21.1 ± 1.5
Labyrinthine zone component volume fraction (%)
LT	50.2 ± 1.7	53.9 ± 0.9	48.8 ± 1.6	48.7 ± 1.4†
MBS	27.5 ± 0.9	28.2 ± 1.0	28.0 ± 0.9	29.9 ± 1.0
FC	26.1 ± 2.0	20.5 ± 1.0	27.4 ± 1.4	25.2 ± 2.2
Surface area of the trophoblast membrane (cm2)
Fetal side	13.3 ± 1.4	8.9 ± 1.2*	22.1 ± 2.2†	16.2 ± 2.4*†
Maternal side	13.8 ± 1.7	17.3 ± 1.8	31.6 ± 3.2†	26.4 ± 3.4†
Mean	13.6 ± 0.5	13.1 ± 0.9	23.5 ± 4.0†	18.6 ± 3.4†
Harmonic mean thickness (μm)	3.78 ± 0.2	3.95 ± 0.3	2.95 ± 0.1†	3.05 ± 0.1†
Theoretical diffusion capacity (mm2 min−1 kPa−1)	6.3 ± 0.4	5.8 ± 0.6	17.2 ± 1.4†	16.5 ± 1.1†
Mean surface area/gram placenta (cm2 g−1)	124 ± 4	170 ± 10*	257 ± 18†	289 ± 22†

Mean (± s.e.m.). Abbreviations: Db, decidua basalis; FC, fetal capillaries; H, heaviest placenta; Jz, junctional zone; L, lightest placenta; LT, labyrinthine trophoblast; Lz, labyrinthine zone; MBS, maternal blood spaces. Analysis was performed on 5 H and 5 L placentas from 5 litters at E16 and from 8 H and 8 L placentas from 8 litters at E19.

^*Significant differences between H and L placentas at the same gestational age (P < 0.05, paired t test).

^†Significant difference between E16 and E19 within the same weight group (P < 0.05, unpaired t test).