Third-trimester nausea often comes as a surprise, since queasiness is typically associated with the first three months of pregnancy. The third trimester begins at week 28. While hormonal changes drive early nausea, the discomfort later in pregnancy is largely physical and mechanical. This late-stage nausea is a common experience, affecting many women as their bodies make space for a rapidly growing baby.
Physical Causes: Uterine Pressure and Reflux
The most frequent causes of discomfort and nausea in the final months are related to physical crowding within the abdomen. As the uterus expands to accommodate the growing fetus, it pushes upward on the stomach and diaphragm, displacing the internal organs. This pressure reduces the functional capacity of the stomach, meaning it cannot hold as much food comfortably, often leading to a feeling of fullness and nausea shortly after eating.
High levels of progesterone circulating in the third trimester compound this mechanical pressure. Progesterone is a powerful smooth muscle relaxant, and its effects extend to the lower esophageal sphincter (LES), the ring of muscle that acts as a valve between the esophagus and the stomach. When the LES relaxes too much, stomach acid can easily back up into the esophagus, a condition known as gastroesophageal reflux disease (GERD).
This acid reflux, often felt as heartburn, frequently manifests as nausea and even vomiting, especially when lying down or bending over. The relaxing effect of progesterone also slows down the entire digestive process, meaning food stays in the stomach for longer periods. This sluggish digestion, combined with the decreased space from the enlarging uterus, contributes significantly to the nausea experienced daily. Heartburn affects up to 80% of pregnant individuals and is a major driver of late-stage nausea.
Nausea as a Sign of Impending Labor
For some women, a sudden return of nausea and vomiting in the final days or hours signals that labor is about to begin. This nausea is often a temporary symptom that occurs as the body initiates childbirth.
The body releases compounds called prostaglandins to help ripen the cervix and prepare the uterus for contractions. These prostaglandins also affect the smooth muscle of the digestive tract, which can cause both nausea and loose stools or diarrhea. The hormonal shift that triggers labor can temporarily slow down digestion, contributing to the queasy feeling.
This pre-labor nausea is typically accompanied by other signs, such as strong, regular contractions, increased fatigue, or the loss of the mucus plug (bloody show). While nausea alone is not a reliable predictor of immediate labor, its sudden onset alongside these other symptoms suggests the body is preparing for delivery.
When Nausea Signals Serious Medical Conditions
While most third-trimester nausea is benign, its sudden onset or severe nature, especially when paired with other symptoms, can signal a serious medical complication requiring immediate attention. Preeclampsia is a disorder characterized by high blood pressure and damage to other organ systems, often the liver and kidneys. Nausea and vomiting can be a late symptom of Preeclampsia, particularly if accompanied by a persistent, severe headache or changes in vision like blurred sight or seeing spots.
A more severe, though rare, complication is HELLP syndrome, often considered a variant of preeclampsia. HELLP is an acronym for Hemolysis, Elevated Liver enzymes, and Low Platelet count. The nausea and vomiting in HELLP syndrome are frequently accompanied by intense pain in the upper right side of the abdomen.
Another liver disorder to consider is Intrahepatic Cholestasis of Pregnancy (ICP), which affects the flow of bile. The cardinal symptom of ICP is severe, relentless itching without a rash, often worse on the palms of the hands and soles of the feet. Nausea can also occur with ICP.
Any new or sudden onset of severe nausea, especially with a headache, vision changes, or right-sided abdominal pain, warrants contacting a healthcare provider right away for evaluation.
Practical Strategies for Relief
Managing the common, pressure-related nausea of the third trimester often involves simple adjustments to eating habits and posture. Eating smaller meals more frequently throughout the day is highly effective because it prevents the stomach from becoming overly full. Consuming five or six small portions instead of three large meals can ease the burden on the crowded digestive system.
Dietary choices play a large role in minimizing acid reflux, a major contributor to late-stage nausea. Avoid foods known to aggravate the lower esophageal sphincter, such as spicy, fatty, or highly acidic items like citrus and tomato products. Staying upright for at least an hour after eating allows gravity to help keep stomach contents down and prevents the backflow of acid.
Adjusting the sleeping position can provide significant relief from nighttime nausea and reflux. Elevating the head of the bed, by placing blocks under the bedposts, uses gravity to minimize acid exposure. Sipping on ginger tea or nibbling on ginger candies can help calm the stomach. Chewing sugar-free gum after meals can stimulate saliva production, which naturally neutralizes stomach acid.