The third trimester, beginning around week 28, marks a period of the most rapid fetal growth and development. During these final weeks, the fetus gains the majority of its birth weight and completes the maturation of its organs, requiring a concentrated supply of nutrients from the maternal diet. Adjusting nutritional intake is necessary to support this accelerated growth and prepare for labor and delivery. Focusing on nutrient density over sheer quantity becomes paramount in this final phase of pregnancy.
Caloric and Macronutrient Needs
While the body does not require “eating for two,” a modest increase in energy intake is needed during these final months. Most recommendations suggest consuming an additional 300 to 450 calories per day in the third trimester, depending on pre-pregnancy weight and activity level. These extra calories should come from nutrient-rich sources, such as lean proteins and complex carbohydrates, to provide fuel without causing excess weight gain.
Protein intake is important to support the substantial growth of fetal tissues and the expansion of maternal blood volume. While the current recommended dietary allowance (RDA) is around 71 grams daily, some studies suggest an optimal intake may be closer to 100 grams per day in late gestation. Protein is necessary for the development of the placenta, uterine tissue, and the manufacturing of hormones and enzymes.
Carbohydrates should primarily be sourced from complex, high-fiber options like whole grains, legumes, and starchy vegetables. These foods provide sustained energy and help regulate blood sugar levels. Simple sugars and refined grains should be limited as they lack the necessary fiber and micronutrients for this developmental phase.
Essential Micronutrients for Fetal Development
The final trimester requires a high demand for specific micronutrients transferred to the fetus. Iron requirements nearly double during pregnancy to 27 milligrams per day, peaking in the third trimester. This supports the mother’s increased blood volume and builds the baby’s iron stores for the first six months of life. Heme iron, found in red meat, fish, and poultry, is the most easily absorbed. Non-heme iron from plant sources like fortified cereals, legumes, and dark leafy greens can be enhanced with Vitamin C-rich foods.
Calcium and Vitamin D work together to mineralize the fetal skeleton, a process most intense in the final weeks. Calcium transfer peaks around 330 milligrams per day near 35 weeks. Consistent intake from dairy products, fortified alternatives, and dark green vegetables remains necessary, even though the mother’s body increases its absorption efficiency. Vitamin D is essential for calcium absorption, and many women require supplementation to maintain adequate levels, as sun exposure is often insufficient.
Docosahexaenoic acid (DHA), an Omega-3 fatty acid, is rapidly incorporated into the fetal brain and retina. DHA is a structural component of cell membranes necessary for optimal neurodevelopment and visual function. Fatty fish like salmon, mackerel, and sardines are the richest sources. Dietary guidelines recommend consuming two servings of low-mercury fish weekly or considering a high-quality supplement.
Dietary Strategies for Common Third Trimester Discomforts
The physical changes of the third trimester often bring about uncomfortable symptoms that can be managed with strategic dietary adjustments.
Managing Heartburn
Heartburn is a frequent complaint, resulting from the hormone progesterone relaxing the esophageal sphincter and the growing uterus physically crowding the stomach. To mitigate this, consuming small, frequent meals throughout the day is more effective than three large meals. This avoids overfilling the stomach.
Avoid trigger foods such as spicy, high-fat, acidic items (like citrus and tomatoes), and carbonated beverages. Instead, try bland, soothing foods like oatmeal, yogurt, or almonds, and avoid lying down for at least one to two hours after eating.
Addressing Constipation and Edema
Constipation is a common issue, often worsened by iron supplementation and the hormonal slowdown of the digestive tract. Increasing fiber intake to a target of 25 to 35 grams daily is the primary solution, using sources like legumes, whole grains, and prunes. Fiber must be paired with generous fluid consumption, which helps bulk and soften the stool for easier passage.
Edema, or swelling, results from increased fluid volume and pressure on the veins. Drinking enough water helps the kidneys flush out excess sodium, despite hydration seeming counterintuitive. Managing sodium intake by limiting processed foods is important. Increasing potassium-rich foods like bananas, sweet potatoes, and avocado helps maintain fluid balance and reduce swelling.
Food Safety and Hydration Guidelines
Maintaining proper hydration in the third trimester is important for preventing preterm contractions. Dehydration can cause the body to release vasopressin, a hormone structurally similar to oxytocin, which causes the uterus to contract. Aiming for 8 to 12 cups of water or other fluids daily helps maintain blood volume and minimize the risk of uterine irritability.
Food safety precautions are paramount, as hormonal changes suppress the immune system, making pregnant individuals susceptible to foodborne illnesses like listeriosis. Listeria bacteria can be harmful, potentially leading to premature delivery or stillbirth, and grows even at refrigeration temperatures. High-risk foods to avoid include:
- Unpasteurized dairy products and juices.
- Soft cheeses like Brie and Feta unless cooked.
- Refrigerated pâtés.
- Cold cuts unless heated until steaming hot.
Limiting caffeine intake is a final safety consideration, with a maximum recommendation of 200 milligrams per day. The mother’s body processes caffeine much slower in the third trimester, increasing the duration of exposure for the fetus. It is also wise to consume coffee or tea between meals, rather than with them, as these beverages can interfere with iron absorption.