Nutrition in Pregnancy
Weight
one of most important determinants of neonatal mobidity and mortality is birthweight (>2500g is good)
- influenced by:
- length of gestation
- maternal weight gain
- preconceptual maternal weight
Þ all of these are influenced by maternal nutrition
smoking or exposure to smoke is associated with a low birthweight (even corrected for nutritional differences in smokers)
weight gain during pregnancy:should be between 24 - 27 pounds, but is highly variable
Þ 28 - 40 pounds
normal (BMI 19.8 - 26) Þ 25 - 35 pounds
over weight (BMI > 26) Þ 15 - 25 pounds
rate of weight gain is as important as total weight gain
- gain is at a low rate for the first 15 wks (~1.6 kg total), then increases to 0.4 kg/wk
extra energy requirements are not constant through pregnancy
- minimal increase during first trimester
- second trimester reflects maternal need (blood volume, uterine and breast growth, muscle, bone density etc)
- third trimester is mostly fetal and placental growth
Þ approx. average of 300 kcal/day above the recommended allowances are required (15% increase)
Þ protein should be increased to ~80 - 100 g/day
Iron
fetus obtains its iron from the mother in a parasitic fashion Þ maternal Fe deficiency ¹ fetal anemia
- most fetal anemia arises from prematurity (fetus gets most Fe during the third trimester)
- however, mom may become anemic
maternal plasma and RBC both rise, but disproportionately Þ hemodilution: hematocrit usually drops (this is normal)
- if the crit doesn’t drop, could be indicative of a poor increase in plasma volume
Fe supplements
- non-heme Fe absorption increases from 7% to 66% by 36 wks
Þ this works in mom’s favor
supplements are still recommended (30 - 60 mg/day)
must also supplement other divalent ions because Fe will competitively compete for absorption
side effects of Fe: stomach distress, constipation
Zinc
deficiency can lead to severe defects: CNS, skeletal, lung, pancreas
low intake is common and can be complicated by Fe supplements
zinc has function in protein regulation (Zn fingers); metalloenzymes; immune function
prenatal supplements: 20 - 25 mg/day
Folate
deficiency could lead to megaloblastic anemia (also complicated by other factors - B12, effects of increased hormones)
most important concern for the fetus are neural tube defects (NTD)
- arise in day 17 - 30
- folate deficiency even before conception can lead to increased risk
Þ FDA mandates folate fortification of many grain foods, but this is still not enough
Þ women of child-bearing age are recommended 0.4 mg/day
folate supplements cannot decrease the risk of NTD associated with obesity
caution: folate supplements can mask a B12 deficiency
Iodine
can lead to endemic cretinism: mental deficiency, deaf-mutism, motor rigidity, hypothyroidism
estimated 20 million people worldwide have brain damage associated with iodine deficiency
Vitamin Toxicity
vitamin A
intake of more than 10,000 IU per day (recommended 3k) is associated with cranial/neural crest defects:
microencephaly, hydrocephaly, small eyes, ears, etc.
also associated with vitamin A analogs like accutane (isotretinoin) used in treatment of acne