Gestation vs. Birthweight

Birthweight (in grams) vs. Gestation time

The CDC has better data on this, but pregnant women frequently wonder whether their late babies will be huge so I asked my survey participants for weight just for funzies. On average, babies born later are slightly bigger but not much. The difference between a baby born around 39W 0D (about 3400 g) and one born around 41 W 0D (about 3700 g) is only 300 g, or about 10.6 ounces.

There's a lot of variety too; plenty of babies born after 41 weeks weigh less than babies born around week 38 or even 37. It should be no surprise that they all just seem to grow at their own rate.

Data table

Date	# Births	Average (g)	± 3 day Average (g)	Change from previous week	± 3 day Average (lbs oz)
35W,0D	23	2692	2756		6 lbs, 1 oz
35W,1D	26	2644	2754		6 lbs, 1 oz
35W,2D	24	2836	2744		6 lbs, 1 oz
35W,3D	33	2831	2746		6 lbs, 1 oz
35W,4D	21	2742	2779		6 lbs, 2 oz
35W,5D	33	2707	2765		6 lbs, 2 oz
35W,6D	24	2759	2779		6 lbs, 2 oz
36W,0D	51	2856	2802	46 g (1.6 oz)	6 lbs, 3 oz
36W,1D	42	2624	2819	65 g (2.3 oz)	6 lbs, 3 oz
36W,2D	54	2862	2865	121 g (4.3 oz)	6 lbs, 5 oz
36W,3D	51	2935	2920	174 g (6.1 oz)	6 lbs, 7 oz
36W,4D	46	2889	2942	163 g (5.7 oz)	6 lbs, 8 oz
36W,5D	60	3008	2973	208 g (7.3 oz)	6 lbs, 9 oz
36W,6D	74	3110	3011	232 g (8.2 oz)	6 lbs, 10 oz
37W,0D	120	2977	3031	229 g (8.1 oz)	6 lbs, 11 oz
37W,1D	118	2968	3062	243 g (8.6 oz)	6 lbs, 12 oz
37W,2D	116	3110	3089	224 g (7.9 oz)	6 lbs, 13 oz
37W,3D	119	3086	3095	175 g (6.2 oz)	6 lbs, 13 oz
37W,4D	146	3147	3139	197 g (6.9 oz)	6 lbs, 15 oz
37W,5D	138	3202	3171	198 g (7 oz)	6 lbs, 16 oz
37W,6D	180	3130	3190	179 g (6.3 oz)	7 lbs, 1 oz
38W,0D	254	3222	3223	192 g (6.8 oz)	7 lbs, 2 oz
38W,1D	222	3222	3255	193 g (6.8 oz)	7 lbs, 3 oz
38W,2D	221	3245	3270	181 g (6.4 oz)	7 lbs, 3 oz
38W,3D	260	3324	3302	207 g (7.3 oz)	7 lbs, 4 oz
38W,4D	336	3341	3327	188 g (6.6 oz)	7 lbs, 5 oz
38W,5D	314	3318	3351	180 g (6.3 oz)	7 lbs, 6 oz
38W,6D	363	3376	3364	174 g (6.1 oz)	7 lbs, 7 oz
39W,0D	525	3368	3385	162 g (5.7 oz)	7 lbs, 7 oz
39W,1D	463	3408	3400	145 g (5.1 oz)	7 lbs, 8 oz
39W,2D	419	3378	3414	144 g (5.1 oz)	7 lbs, 8 oz
39W,3D	555	3456	3433	131 g (4.6 oz)	7 lbs, 9 oz
39W,4D	561	3447	3462	135 g (4.8 oz)	7 lbs, 10 oz
39W,5D	542	3437	3483	132 g (4.7 oz)	7 lbs, 11 oz
39W,6D	589	3512	3504	140 g (4.9 oz)	7 lbs, 12 oz
40W,0D	1095	3512	3522	137 g (4.8 oz)	7 lbs, 12 oz
40W,1D	701	3560	3539	139 g (4.9 oz)	7 lbs, 13 oz
40W,2D	638	3570	3560	146 g (5.1 oz)	7 lbs, 14 oz
40W,3D	596	3599	3576	143 g (5 oz)	7 lbs, 14 oz
40W,4D	572	3596	3605	143 g (5 oz)	7 lbs, 15 oz
40W,5D	586	3611	3620	137 g (4.8 oz)	7 lbs, 16 oz
40W,6D	604	3638	3639	135 g (4.8 oz)	8 lbs, 0 oz
41W,0D	662	3665	3654	132 g (4.7 oz)	8 lbs, 1 oz
41W,1D	541	3659	3669	130 g (4.6 oz)	8 lbs, 1 oz
41W,2D	439	3721	3689	129 g (4.6 oz)	8 lbs, 2 oz
41W,3D	435	3718	3702	126 g (4.4 oz)	8 lbs, 3 oz
41W,4D	330	3716	3720	115 g (4.1 oz)	8 lbs, 3 oz
41W,5D	263	3791	3740	120 g (4.2 oz)	8 lbs, 4 oz
41W,6D	220	3727	3749	110 g (3.9 oz)	8 lbs, 4 oz
42W,0D	204	3790	3771	117 g (4.1 oz)	8 lbs, 5 oz
42W,1D	117	3780	3793	124 g (4.4 oz)	8 lbs, 6 oz
42W,2D	69	3848	3797	108 g (3.8 oz)	8 lbs, 6 oz
42W,3D	48	4032	3830	128 g (4.5 oz)	8 lbs, 7 oz
42W,4D	19	3891	3846	126 g (4.4 oz)	8 lbs, 8 oz
42W,5D	25	3877	3886	146 g (5.1 oz)	8 lbs, 9 oz
42W,6D	12	3898	3908	159 g (5.6 oz)	8 lbs, 10 oz

Total responses: 15317