Miscarriage is medically defined as the spontaneous loss of a pregnancy before 20 weeks of gestation. While certain foods pose health hazards to a developing pregnancy, dietary factors are rarely the primary cause of a loss. This article provides evidence-based information to separate real hazards from unfounded fears regarding food choices during pregnancy.
Primary Causes of Miscarriage
The focus on diet as a cause for miscarriage is often misplaced because the vast majority of losses are due to factors beyond a person’s control. Approximately 50% to 70% of first-trimester miscarriages are the result of a random, non-preventable chromosomal abnormality in the fetus. These are typically one-time genetic errors that prevent the embryo from developing correctly, making the pregnancy genetically non-viable from the start.
Other factors, like hormonal imbalances, problems with the structure of the uterus, or underlying health conditions such as uncontrolled diabetes or thyroid issues, account for a much smaller percentage of miscarriages. Understanding the high prevalence of these spontaneous genetic events helps clarify that a loss is rarely caused by a preventable action, such as diet.
Foodborne Illness: The Real Dietary Risk
When diet contributes to an adverse pregnancy outcome, it is usually through contamination by harmful microorganisms, not the inherent nature of the food itself. Two pathogenic organisms present a significant risk: the bacterium Listeria monocytogenes (Listeriosis) and the parasite Toxoplasma gondii (Toxoplasmosis). These infections are dangerous because pregnancy alters the immune response, making the parent more vulnerable.
Listeria monocytogenes can cause mild or asymptomatic illness in the parent but has a strong affinity for the placenta. The bacterium crosses the placental barrier and infects the fetus, which can lead to severe consequences, including miscarriage, stillbirth, or severe illness in a newborn. Infection with Listeria in the first trimester carries a risk of spontaneous abortion estimated at 65%.
Toxoplasma gondii is often transmitted through consuming raw or undercooked meat. While the infection is mild in an adult, it can pass to the fetus through the placenta. Congenital toxoplasmosis can result in severe complications for the baby, including developmental delays, vision loss, or neurological problems. Avoiding specific foods that harbor these pathogens is a primary way to prevent these serious infections.
Specific Foods and Ingredients to Avoid
Foods that present a genuine risk are those prone to contamination or those containing substances harmful in high doses. To minimize the risk of Listeriosis, avoid unpasteurized dairy products, including milk and soft cheeses like Brie, Camembert, Feta, and fresh mozzarella, unless the label explicitly states they are made with pasteurized milk.
Refrigerated meat spreads, pâtés, and deli or luncheon meats are also susceptible to Listeria contamination. These items should be avoided or thoroughly reheated until steaming hot.
The risk of Toxoplasmosis, Salmonella, and other bacteria requires avoiding raw or undercooked meats, poultry, and seafood, including sushi made with raw fish. All meats must be cooked to their safe internal temperatures. Raw eggs, found in some homemade sauces, should also be avoided due to the potential for Salmonella.
Beyond pathogens, certain substances must be limited or avoided due to their toxic effects on the developing fetus. Large predatory fish accumulate high levels of mercury, a neurotoxin that can impair fetal brain development. These include:
- Shark
- Swordfish
- King mackerel
- Tilefish
Daily caffeine intake should be limited to 200 milligrams or less, which is roughly one to two cups of coffee, as higher consumption has been linked to an increased risk of miscarriage. High-dose Vitamin A supplements, specifically those containing the retinoid form, should also be avoided, as excessive amounts can be harmful.
Dispelling Common Food Misconceptions
Many foods commonly believed to cause miscarriage are safe to consume in moderation. The myth that spicy foods can induce labor or cause miscarriage is unfounded, as capsaicin, the compound that makes food spicy, does not affect the uterus. Eating spicy meals is safe, though it may increase heartburn.
Pineapple is frequently cited as a forbidden food due to its content of the enzyme bromelain. While concentrated bromelain in tablet form is not recommended, the amount naturally present in pineapple is too low to cause uterine contractions or miscarriage. Moderate consumption of other fruits like papaya and mango presents no danger. A varied, healthy diet focused on food safety is the best approach, and unfounded fears about specific fruits should not limit nutritional intake.