TABLE 2.

Combined fetal and neonatal cardiomyocyte data sets that are statistically best fit by regression of 2 intersecting straight lines, in which the left (“fetal”) segment takes the form y = slope_f (dPC) + intercept_f, the right (“neonatal”) segment takes the form y = slope_f (X₀) + intercept_f + slope_n (dPC – X₀), intersecting at x = X₀ (“breakpoint”)

Parameter	Fetal segment	X0, mean (95% CI)	Neonatal segment	Goodness of fit (R2)	Model comparison
Weight
Log body weight (kg)	0.0183 dPC − 1.831	128.6 (121.8–135.4)	0.01044 (dPC − 128.6) + 0.52238	0.9631	P < 0.0001
Log heart weight (g)	0.01813 dPC − 0.9569	128 (120.0–136.0)	0.009203 (dPC − 128) + 1.366374	0.9297	P < 0.0001
LV weight (g)	0.1425 dPC − 12.03	143.3 (136.4–150.2)	0.5833 (dPC − 143.3) + 8.39025	0.964	P < 0.0001
RV weight (g)	0.1381 dPC − 11.85	163 (142.0–184.0)	0.2689 (dPC − 163) + 10.6603	0.9430	P = 0.0002
Cell length and width (μm)
LV mononucleate length	−0.08488 dPC + 68.64	118.6 (108.5–128.6)	0.3906 (dPC − 118.6) + 58.573232	0.7371	P < 0.0001
LV binucleate length	−0.1434 dPC + 99.16	132.2 (124.9–139.4)	0.6583 (dPC − 132.2) + 80.20252	0.7252	P < 0.0001
LV mononucleate width	0.0133 dPC + 8.298	125.7 (119.3–132.1)	0.1449 (dPC − 125.7) + 9.96981	0.8907	P < 0.0001
LV binucleate width	−0.0207 dPC + 13.42	124.9 (119.1–130.6)	0.1918(dPC − 124.9) + 10.83457	0.8647	P < 0.0001
RV mononucleate length	−0.2056 dPC + 90.4	128.2 (122.4–134.0)	0.4051 (dPC − 128.2) + 64.04208	0.6993	P < 0.0001
RV binucleate length	−0.195 dPC + 113.9	132.7 (124.6–140.8)	0.534 (dPC − 132.7) + 88.0235	0.615	P < 0.0001
Cell length:width ratio
RV mononucleated length:width	−0.04222 dPC + 10.13	120 (107.4–132.6)	0.002037 (dPC − 120) + 5.0636	0.275	P < 0.001
RV binucleate length:width	−0.02816 dPC + 9.625	145.4 (118.9–172.0)	0.007378 (dPC − 145.4) + 5.530536	0.1888	P < 0.05
Cell volume (μm3)
LV mononucleate volume	38.83 dPC − 1754	140.4 (135.7–145.1)	242.1 (dPC − 140.4) + 3697.732	0.9262	P < 0.0001
LV binucleate volume,	35.35 dPC + 819.8	137.6 (133.3–141.8)	476 (dPC − 137.6) + 5683.96	0.9161	P < 0.0001
RV mononucleate volume	27.39 dPC + 1352	129 (119.3–138.7)	120 (dPC − 129) + 4885.31	0.8241	P < 0.0001
RV binucleate volume	47.24 dPC + 3436	130.5 (117.7–143.3)	228.7 (dPC − 130.5) + 9600.82	0.7252	P = 0.0005
Myocyte and nuclei number (109)
LV fetal period myocyte number	0.02619 dPC − 1.970	135.9 (133.6–138.2)	−0.1125 (dPC − 135.9) + 1.589221	0.6150	P < 0.0001
LV fetal period nuclei number	0.0433 dPC − 3.703	136.0 (132.6–139.5)	−0.1155 (dPC − 136.0) + 2.1858	0.7027	P = 0.0005
RV fetal period myocyte number	0.0185 dPC − 1.534	136 (133.3–138.7)	−0.075 (dPC - 136) + 0.982	0.6317	P < 0.0001
RV fetal period nuclei number	0.02801 dPC - 2.499	136 (132.0–140.0)	−0.06005 (dPC − 136) + 1.31036	0.7205	P < 0.002
LV cell cycle activity (% of all myocytes)	−0.1498 dPC + 21.64	131.3 (117.3–145.4)	−0.0292 (dPC − 131.3) + 1.97126	0.5719	P = 0.0007
Number of nuclei per cell (%)
LV quadrinucleation	0.001477 dPC − 0.1086	142.4 (133.3–151.6)	0.1142 (dPC − 142.4) + 0.1017248	0.6815	P < 0.0001
RV quadrinucleation	−3.879 (10−10) dPC − 4.903 (10−08)	124.4 (110.3–138.4)	0.03695 (dPC − 124.4) − 7.7524 (10−10)	0.5651	P < 0.004