Place · Level 3
Pregnancy & Lactation Nutrition · The why behind it
叶酸要在怀孕前就开始 · 碘和胆碱也建大脑 · 吃两人份是误区 · DHA 减早产不是提智商 · 一切跟着你的产科医生
Story path
- 1Folate · a door that shuts earlyFolate · a door that shuts early
- 2Two more brain-building nutrientsTwo more brain-building nutrients
- 3Iron · making more bloodIron · making more blood
- 4Where marketing outruns evidenceWhere marketing outruns evidence
- 5'Eating for two' + what to avoid'Eating for two' + what to avoid
- 6Lactation + the galactagogue truthLactation + the galactagogue truth
Chapter 1
Folate · a door that shuts early
Folate · a door that shuts early
The first thing to say about pregnancy nutrition is folate. The reason hides in the calendar: the fetal neural tube (the future brain and spinal cord) closes at about 24-28 days after conception — when many people don't yet know they're pregnant and haven't even missed a period.
So taking folate is something to start before pregnancy, not 'mention at the first prenatal visit'. Mechanistically, folate supplies the methyl groups the fast-dividing neural-tube cells need to build DNA. The general-population recommendation is 400-800 micrograms a day (USPSTF Grade A).
About that often-quoted 72%: it comes from the landmark 1991 MRC RCT and refers to high-risk women who already had a baby with a neural tube defect, using a high 4 mg/day dose, where recurrence risk fell 72% (RR 0.28). Don't attach that number to the everyday 400 micrograms — the population and the dose are different.
While we're here, one marketing claim to dismantle: that 'an MTHFR gene variant means you must take active folate (L-methylfolate)'. Guidelines (ACMG) don't recommend routinely testing that gene; ordinary folic acid works regardless of genotype, and 'active folate is better' is a sales pitch, not an evidence-based recommendation.
So taking folate is something to start before pregnancy, not 'mention at the first prenatal visit'. Mechanistically, folate supplies the methyl groups the fast-dividing neural-tube cells need to build DNA. The general-population recommendation is 400-800 micrograms a day (USPSTF Grade A).
About that often-quoted 72%: it comes from the landmark 1991 MRC RCT and refers to high-risk women who already had a baby with a neural tube defect, using a high 4 mg/day dose, where recurrence risk fell 72% (RR 0.28). Don't attach that number to the everyday 400 micrograms — the population and the dose are different.
While we're here, one marketing claim to dismantle: that 'an MTHFR gene variant means you must take active folate (L-methylfolate)'. Guidelines (ACMG) don't recommend routinely testing that gene; ordinary folic acid works regardless of genotype, and 'active folate is better' is a sales pitch, not an evidence-based recommendation.
Chapter 2
Two more brain-building nutrients
Two more brain-building nutrients
Besides folate, two more nutrients help build the brain but are often overlooked.
Iodine is the raw material for thyroid hormone, and thyroid hormone directly governs fetal brain development. The WHO calls iodine deficiency 'the world's most prevalent, yet easily preventable, cause of brain damage'. The pregnancy requirement rises to about 250 micrograms a day (WHO), and the American Thyroid Association recommends an extra 150 microgram iodine supplement because many prenatal vitamins contain none.
Choline is the most under-appreciated one. Its adequate intake (AI) is 450 milligrams a day, yet about 90% of pregnant people fall short, and prenatal vitamins usually contain little if any. Choline matters for the fetal brain in animals and mechanistically; but to be honest, the human cognitive benefit so far rests on one very small RCT (about 26 people, on a surrogate outcome) — so the wording should be 'may help', not 'makes babies smarter'.
Iodine is the raw material for thyroid hormone, and thyroid hormone directly governs fetal brain development. The WHO calls iodine deficiency 'the world's most prevalent, yet easily preventable, cause of brain damage'. The pregnancy requirement rises to about 250 micrograms a day (WHO), and the American Thyroid Association recommends an extra 150 microgram iodine supplement because many prenatal vitamins contain none.
Choline is the most under-appreciated one. Its adequate intake (AI) is 450 milligrams a day, yet about 90% of pregnant people fall short, and prenatal vitamins usually contain little if any. Choline matters for the fetal brain in animals and mechanistically; but to be honest, the human cognitive benefit so far rests on one very small RCT (about 26 people, on a surrogate outcome) — so the wording should be 'may help', not 'makes babies smarter'.
Chapter 3
Iron · making more blood
Iron · making more blood
In pregnancy, the plasma (the liquid part of blood) expands by about 40-50%, while red-cell numbers can't keep pace — so the blood is diluted and labs can look anemic (physiologic dilutional anemia); on top of that, the fetus and placenta genuinely need iron. So the iron recommendation rises from 18 to 27 milligrams a day.
Here's a real, worth-knowing guideline disagreement:
The American College of Obstetricians and Gynecologists (ACOG): screen every pregnant person with a blood count (first trimester + 24-28 weeks) for anemiaUSPSTF 2024: gave routine screening and supplementation in asymptomatic pregnant people an 'I' (insufficient evidence) rating
Read that 'I' correctly: it means the current evidence is insufficient to weigh benefit against harm — not 'don't screen'; and it explicitly excludes symptomatic and high-risk people. The two sides are a documented disagreement, not a right-and-wrong — what to actually do, follow your OB.
Here's a real, worth-knowing guideline disagreement:
The American College of Obstetricians and Gynecologists (ACOG): screen every pregnant person with a blood count (first trimester + 24-28 weeks) for anemiaUSPSTF 2024: gave routine screening and supplementation in asymptomatic pregnant people an 'I' (insufficient evidence) rating
Read that 'I' correctly: it means the current evidence is insufficient to weigh benefit against harm — not 'don't screen'; and it explicitly excludes symptomatic and high-risk people. The two sides are a documented disagreement, not a right-and-wrong — what to actually do, follow your OB.
Chapter 4
Where marketing outruns evidence
Where marketing outruns evidence
This screen is for building judgment: two nutrients sold hard, on evidence that's less miraculous than the pitch.
DHA (an omega-3): the genuinely solid benefit is reducing preterm birth (Cochrane: <37 weeks RR 0.89, <34 weeks RR 0.58), not raising IQ. The most-quoted 'DHA makes babies smarter' largely fell flat in big trials (DOMInO, followed to age 4, no cognitive difference). So the reason to take DHA in pregnancy is preterm protection, not 'a smarter baby'.
Vitamin D: the recommendation is 600 IU a day. After its 2024 update, Cochrane downgraded the claims about preventing pre-eclampsia, gestational diabetes, and improving birthweight to low or very-low certainty (the confidence intervals all cross the line of no effect). ACOG doesn't recommend routinely screening everyone's vitamin D — rather, supplement when there's documented deficiency (1,000-2,000 IU).
The takeaway: neither is 'more is better, everyone megadose' — it's about being clear on what to supplement, and for whom.
DHA (an omega-3): the genuinely solid benefit is reducing preterm birth (Cochrane: <37 weeks RR 0.89, <34 weeks RR 0.58), not raising IQ. The most-quoted 'DHA makes babies smarter' largely fell flat in big trials (DOMInO, followed to age 4, no cognitive difference). So the reason to take DHA in pregnancy is preterm protection, not 'a smarter baby'.
Vitamin D: the recommendation is 600 IU a day. After its 2024 update, Cochrane downgraded the claims about preventing pre-eclampsia, gestational diabetes, and improving birthweight to low or very-low certainty (the confidence intervals all cross the line of no effect). ACOG doesn't recommend routinely screening everyone's vitamin D — rather, supplement when there's documented deficiency (1,000-2,000 IU).
The takeaway: neither is 'more is better, everyone megadose' — it's about being clear on what to supplement, and for whom.
Chapter 5
'Eating for two' + what to avoid
'Eating for two' + what to avoid
'Eating for two' is a widespread myth. The extra energy is actually modest: about +0 kcal in the first trimester, ~+340 kcal in the second, ~+450 kcal in the third (IOM 2005) — roughly a snack or two, not double.
More important than 'eating more' is avoiding a few things, in order of certainty:
Alcohol: no known safe amount and no safe window (CDC / ACOG / US Surgeon General agree). This is the firmest — put it first.High-dose preformed vitamin A (retinol): above about 10,000 IU/day carries teratogenic risk (Rothman 1995, a prospective cohort). Note — beta-carotene is not teratogenic (the body converts it as needed), so carrots and squash are fine; the things to watch are animal liver and high-dose vitamin A supplements.High-mercury fish: avoid per the FDA/EPA 2021 list (shark, swordfish, king mackerel, Gulf of Mexico tilefish), and eat 8-12 oz/week of lower-mercury fish instead.Listeria-prone foods: unpasteurized cheeses, deli meats, raw items (pregnancy raises infection risk far above baseline).
This avoid list is worth remembering more than any 'what to supplement'.
More important than 'eating more' is avoiding a few things, in order of certainty:
Alcohol: no known safe amount and no safe window (CDC / ACOG / US Surgeon General agree). This is the firmest — put it first.High-dose preformed vitamin A (retinol): above about 10,000 IU/day carries teratogenic risk (Rothman 1995, a prospective cohort). Note — beta-carotene is not teratogenic (the body converts it as needed), so carrots and squash are fine; the things to watch are animal liver and high-dose vitamin A supplements.High-mercury fish: avoid per the FDA/EPA 2021 list (shark, swordfish, king mackerel, Gulf of Mexico tilefish), and eat 8-12 oz/week of lower-mercury fish instead.Listeria-prone foods: unpasteurized cheeses, deli meats, raw items (pregnancy raises infection risk far above baseline).
This avoid list is worth remembering more than any 'what to supplement'.
Chapter 6
Lactation + the galactagogue truth
Lactation + the galactagogue truth
After birth, lactation does need a bit more energy, but less than imagined: a net increase of about 330 kcal/day (the often-heard 500 kcal is the gross cost of making milk, of which about 170 kcal comes from fat stored during pregnancy — so the amount you actually eat more is 330).
Two common myths:
'Chugging water makes more milk' — no evidence. A Cochrane review found that drinking beyond thirst doesn't raise supply. Drink to thirst is enough.'Galactagogue supplements (fenugreek, fennel, milk thistle) work' — the evidence is low to very-low certainty (2020 Cochrane); the Academy of Breastfeeding Medicine (ABM) explicitly cannot recommend any specific galactagogue, and the apparent effect may just be placebo. The first-line fix for low supply is effective, frequent milk removal, not herbs. (Safety note: fenugreek is a legume, so people allergic to peanuts/chickpeas may cross-react; it can also cause GI upset and lower blood sugar.)
To close: this page is general education to understand the why, not medical advice. Perinatal nutrition is highly individual — medications, existing conditions, prior pregnancies, diet, and labs all matter — so decide together with your OB or midwife. For the avoid-list, remember the highest-certainty ones first: alcohol and high-dose vitamin A.
Two common myths:
'Chugging water makes more milk' — no evidence. A Cochrane review found that drinking beyond thirst doesn't raise supply. Drink to thirst is enough.'Galactagogue supplements (fenugreek, fennel, milk thistle) work' — the evidence is low to very-low certainty (2020 Cochrane); the Academy of Breastfeeding Medicine (ABM) explicitly cannot recommend any specific galactagogue, and the apparent effect may just be placebo. The first-line fix for low supply is effective, frequent milk removal, not herbs. (Safety note: fenugreek is a legume, so people allergic to peanuts/chickpeas may cross-react; it can also cause GI upset and lower blood sugar.)
To close: this page is general education to understand the why, not medical advice. Perinatal nutrition is highly individual — medications, existing conditions, prior pregnancies, diet, and labs all matter — so decide together with your OB or midwife. For the avoid-list, remember the highest-certainty ones first: alcohol and high-dose vitamin A.