Skip to main content
. 2022 Dec 19;117(2):227–234. doi: 10.1016/j.ajcnut.2022.09.005

TABLE 2.

Rationale for the suggested update to the 2005 Institute of Medicine recommendation for carbohydrate intake during pregnancy

EAR nonpregnant adults1 Fetal brain glucose utilization2 Placental glucose consumption3 Total EAR Conversion to RDA
100 g/d 35 g/d 36 g/d 171 g/d 222 g/d Round down: 220 g/d
  • -

    Range of average brain O2 consumption in adults is ∼3.3–4.2 mL/100 g/min (24% difference across the range) (21)

  • -

    Based on 1.4 kg brain weight in adults, the brain consumes ∼91 g glucose/d.

  • -

    Cerebral metabolic rate for glucose: 0.25 μmol/g/min, range of 0.2–0.3 μmol/g/min or a 40% difference across the range (21)

  • -

    Based on these more recent data, the original obligate brain glucose requirement appears to remain appropriate at 100 g/d

 -Maternal-fetal glucose gradient: 23 mg/dL (20) Average placental weight (n = 179; mean ± SD): 617 ± 113 g (20) 100 g + 35 g + 36 g = 171 g/d ([100 g + 35 g + 36 g) ∗ 15%] ∗ 2 + 171 g = 222 g/d Round down: 220 g/d
Median fetal whole-body glucose consumption (20): Placental weight ranges (36) (n = 98, 39 wks, Ireland)
96.8 μmol ∗ min-1 (52.7, 144.5) 10th centile: 489 g
(median, first, and third quartiles) 50th centile: 630 g
Median:
96.8 μmol/L∗ min = 17.4395 mg/L
17.4395 ∗ 1440 min/24 h = 25,112.88 mg or 25.1g/d (round to 25 mg/d)		 90th centile: 836 g
Range: 409–637 g (n = 21, Philippines) (37)
Based on this, assume placental weight 617 + 113 (1 SD) = 750 g or 0.75 kg (20)
-Placental glucose consumption adjusted for placental weight (20) was
51.4 μmol ∗ min-1 ∗ kg-1 [–65.8, 185.4]
First quartile:
52.7 μmol/L∗ min = 9.4944 mg/L
9.4944 ∗ 1440 min/24 h = 13,671.936 mg or 13.7 g/d (round to 14 g/d)		 (median, first, and third quartiles)
Median:
51.4 μmol/L ∗ min ∗ kg = 9.2602 mg/L 9.2602 ∗ 1440 min/24 h = 13,334.688 mg
13,334.688 ∗ 0.75 kg = 10,001.016 mg or 10 g/d
Third quartile:
185.4 μmol/L ∗ min ∗ kg = 33.4017 mg/L
33.4017 ∗ 1440 min/24 h = 48,098.448 mg
48,098.448 ∗ 0.75 kg = 36,073.836 mg or 36 g/d
Work in pregnant sheep demonstrates placental glucose consumption CV% of 20%–35% (38–40); thus, 15% is likely a conservative estimate
Third quartile:
144.5 μmol/L∗ min = 26.0331 mg/L
26.0331 ∗ 1440 min/24 h = 37,487.664 mg or 37.5 g/d (round to 38 g/d)
  • -

    Based on these more recent data, the original obligate fetal brain glucose requirement appears to remain appropriate to cover fetal whole-body needs (third quartile)

 Apply the same coefficient of variation (15%) and use the estimate from the third quartile for placental glucose consumption

EAR, estimated average requirement

The EAR covers the nutritional carbohydrate needs of ∼50% of the population, whereas the RDA covers the needs of 97%–98% of the population.

1

Contemporary measurements of glucose consumption support that the current EAR remains appropriate for both maternal and

2

Fetal brain glucose requirements.

3

Further data from recent in vivo measurements estimate human placental glucose consumption3 are translated to grams per day of carbohydrate based on 1440 min in 24 h. Consideration of the placenta as an organ highly reliant on glucose as a fuel source would result in an upward adjustment of 45 g/d to the RDA for dietary glucose intake to cover the maternal brain and glycolytic cell function, fetal brain, and placental glucose consumption [46].