2.4 Maternal Nutrition, Weight Gain & Immunization in Pregnancy
Key Takeaways
- Institute of Medicine total weight-gain targets by prepregnancy BMI are 28 to 40 lb if underweight, 25 to 35 lb if normal weight, 15 to 25 lb if overweight, and 11 to 20 lb if obese.
- High-risk patients, including those with a prior neural tube defect, pregestational diabetes, or antiepileptic therapy, require 4 mg of folic acid daily rather than the routine 400 to 800 mcg.
- One dose of Tdap is given in every pregnancy at 27 0/7 to 36 6/7 weeks regardless of prior Tdap history.
- Maternal RSVpreF vaccine is given at 32 0/7 to 36 6/7 weeks during the September through January season, as an alternative to infant nirsevimab rather than in addition to it.
- MMR, varicella, and live attenuated nasal influenza vaccines are contraindicated in pregnancy and are given postpartum before discharge to non-immune patients.
Maternal Nutrition & Weight Gain Guidelines
Institute of Medicine (IOM) Weight Gain Targets
Maternal weight gain recommendations are based strictly on prepregnancy Body Mass Index (BMI) calculated as $\text{BMI} = \text{weight (kg)} / [\text{height (m)}]^2$.
| Prepregnancy BMI Category | BMI Range (kg/m²) | Recommended Total Weight Gain (Singleton) | Mean Weekly Gain in 2nd & 3rd Trimesters |
|---|---|---|---|
| Underweight | <18.5 | 28 to 40 lbs (12.5–18.0 kg) | 1.0 lb/week (0.45 kg/wk) |
| Normal Weight | 18.5–24.9 | 25 to 35 lbs (11.5–16.0 kg) | 1.0 lb/week (0.45 kg/wk) |
| Overweight | 25.0–29.9 | 15 to 25 lbs (7.0–11.5 kg) | 0.6 lb/week (0.28 kg/wk) |
| Obese (all classes) | ≥30.0 | 11 to 20 lbs (5.0–9.0 kg) | 0.5 lb/week (0.22 kg/wk) |
Essential Nutritional & Micronutrient Requirements
- Caloric Needs: No extra calories required in the 1st trimester; +340 kcal/day in the 2nd trimester; +452 kcal/day in the 3rd trimester.
- Folate / Folic Acid:
- Low-risk individuals: 400 to 800 mcg/day orally starting at least 1 month preconception through the first trimester to prevent 70% of neural tube defects.
- High-risk individuals (prior child with NTD, maternal epilepsy on valproate/carbamazepine, pregestational diabetes): 4 mg (4,000 mcg)/day preconceptionally through 12 weeks.
- Elemental Iron: 27 mg/day for routine maintenance. Iron deficiency anemia requires therapeutic supplementation of 60 to 120 mg/day of elemental iron, taken with vitamin C on an empty stomach to enhance absorption.
- Calcium & Vitamin D: 1,000 mg/day of elemental calcium (1,300 mg/day for adolescents <18 years) and 600 IU/day of Vitamin D to maintain maternal bone homeostasis and support fetal skeletal mineral accretion (~300 mg/day transferred to the fetus in late third trimester).
- Omega-3 Fatty Acids (DHA): 200 to 300 mg/day of Docosahexaenoic acid (DHA) to support fetal brain development and retinal arborization.
- Iodine: 220 mcg/day (potassium iodide) for fetal neurodevelopment and thyroid hormone synthesis.
Critical Food Safety Rules in Pregnancy
- Listeria monocytogenes: Intracellular gram-positive bacillus causing chorioamnionitis, septic abortion, stillbirth, and neonatal granulomatosis infantiseptica. Advise avoidance of unpasteurized milk and soft cheeses (feta, brie, camembert, queso fresco), refrigerated pâtés, smoked seafood, and deli cold cuts or hot dogs unless reheated to steaming hot (165°F / 74°C).
- Toxoplasma gondii: Intracellular protozoan causing congenital chorioretinitis, hydrocephalus, and intracranial calcifications. Advise avoidance of raw or undercooked meats, unwashed garden produce, and direct handling of domestic feline litter boxes (assign litter box maintenance to others or wear gloves and wash hands thoroughly).
- Methylmercury: Bioaccumulative neurotoxin causing fetal microcephaly and neurodevelopmental delay. Instruct patients to completely avoid large apex predatory fish: shark, swordfish, king mackerel, tilefish, bigeye tuna, and marlin. Recommend 8–12 ounces per week of low-mercury fish (salmon, canned light tuna, shrimp, pollock, cod, and tilapia).
Immunization During Pregnancy and the Puerperium
Vaccination is a routine antepartum task ("orders immunizations in pregnancy") and a routine postpartum one ("counsels about and orders maternal immunizations in the postpartum period"). Two principles govern everything: inactivated, subunit, toxoid, and mRNA vaccines are safe in pregnancy, while live attenuated vaccines are contraindicated and are deferred to the postpartum period.
Vaccines Recommended During Pregnancy
| Vaccine | Timing | Purpose |
|---|---|---|
| Tdap | One dose in every pregnancy, 27 0/7 to 36 6/7 weeks, preferably early in that window, regardless of prior Tdap history | Transplacental pertussis antibody transfer to protect the newborn before the 2-month DTaP dose |
| Inactivated influenza | Any trimester during influenza season | Pregnancy is a CDC high-risk condition for severe influenza; also protects the infant under 6 months, who cannot be vaccinated |
| COVID-19 | Any trimester; ACOG advises vaccination as soon as it is available in the season | ACOG's 2026 maternal immunization schedule continues to recommend COVID-19 vaccination in pregnancy; federal recommendations have moved toward individual decision-making, so confirm the current schedule and document shared decision-making |
| Maternal RSV (RSVpreF, Abrysvo) | 32 0/7 to 36 6/7 weeks, seasonally (about September through January in most of the continental US) | Protects the infant against severe RSV lower respiratory tract disease. The alternative is infant nirsevimab after birth — give one or the other, not routinely both |
| Hepatitis B | Any trimester if indicated by risk or by universal adult recommendation | Recombinant, not live; safe in pregnancy |
Vaccines Contraindicated During Pregnancy
MMR, varicella, live attenuated influenza (nasal LAIV), and smallpox vaccines are live attenuated and contraindicated. Advise avoidance of conception for 28 days after MMR or varicella vaccination — although inadvertent administration is not an indication for termination, since no case of congenital rubella syndrome has been attributed to the vaccine.
Postpartum Catch-Up
The postpartum stay is the single best opportunity to close immunity gaps identified on the initial prenatal panel.
- Rubella non-immune → MMR before discharge.
- Varicella non-immune → first varicella dose before discharge, second at 4–8 weeks.
- Tdap → if it was somehow missed in pregnancy, give immediately postpartum.
- HPV → offer to eligible patients through age 26 (and by shared decision-making through age 45).
- Breastfeeding is not a contraindication to any of these, including live vaccines.
A 26-year-old primigravida presents for her initial prenatal visit at 10 weeks gestation. Her height is 5 feet 4 inches (163 cm) and weight is 190 lbs (86.2 kg), corresponding to a prepregnancy BMI of 32.6 kg/m² (Class I Obesity). When discussing nutrition and healthy gestational weight gain, which guideline should the certified nurse-midwife provide?
A patient at 29 weeks gestation in mid-October has had an inactivated influenza vaccine this season and reports receiving Tdap three years ago with a previous pregnancy. Her prenatal panel showed she is rubella non-immune. Which immunization plan is correct today?