The return of nausea late in the third trimester often causes alarm, as many people associate morning sickness only with early pregnancy. This late-stage nausea is a common experience as the body prepares for childbirth. Understanding the potential connections between this feeling and the start of labor, as well as recognizing other common causes, can help expecting parents navigate the final stretch of pregnancy. This article explores the physiological link between late-stage nausea and the onset of labor.
Nausea as a Pre-Labor Sign
Nausea can be a subtle sign that the body is beginning the process of labor preparation. This mild stomach upset is often attributed to hormonal shifts that occur as the due date approaches. The body releases compounds called prostaglandins, which play a direct role in softening and ripening the cervix for delivery.
These hormone-like substances also affect the smooth muscle tissues of the digestive tract. The influence of prostaglandins can lead to increased intestinal activity, which may manifest as mild nausea, loose stools, or even a brief episode of vomiting. This effect is sometimes described as the body “clearing out” before labor begins, typically occurring within 24 to 48 hours of true labor starting.
The nausea connected to labor is generally mild and short-lived, unlike the persistent sickness of the first trimester. When this queasiness appears alongside other subtle changes, such as the loss of the mucus plug (the “bloody show”) or an unusual burst of energy often called “nesting,” it may indicate that the birthing process is near. It is not a standalone predictor, but rather a supporting symptom in the collection of early labor signs.
Other Causes of Late-Pregnancy Nausea
Not all late-pregnancy nausea signals an imminent labor, as the discomfort can often be traced back to non-labor-related physical and digestive changes. As the fetus grows, the expanding uterus takes up an increasing amount of space in the abdominal cavity, placing significant physical pressure on the stomach and surrounding organs. This compression of the stomach makes it easier for gastric contents to back up, which frequently leads to severe acid reflux or gastroesophageal reflux disease (GERD).
Hormonal changes also contribute to digestive distress, particularly the sustained high levels of progesterone. Progesterone has a relaxing effect on the body’s smooth muscles, including those lining the digestive tract, which slows down the movement of food through the intestines. The slower digestion, combined with the physical crowding of the stomach, can result in feelings of fullness, bloating, and nausea, especially after eating a large meal. Simple dietary factors, such as eating too quickly or consuming foods that are spicy, fatty, or highly acidic, can also aggravate an already sensitive digestive system in the third trimester.
When to Seek Medical Attention
While mild nausea is often a benign symptom of late pregnancy or impending labor, severe or sudden onset of vomiting requires immediate medical attention. The most serious concern is when nausea is accompanied by specific symptoms that could indicate a complication like preeclampsia. Preeclampsia is a blood pressure disorder that usually develops after 20 weeks of gestation.
A healthcare provider should be contacted immediately if severe nausea or vomiting is paired with a persistent, intense headache that does not improve with common remedies. Other danger signs include sudden visual changes, such as blurred vision, flashing lights, or spots. Pain in the upper abdomen, specifically under the ribs on the right side, can also be a significant warning sign that should not be ignored. These symptoms, even without labor contractions, suggest a need for urgent medical evaluation to rule out a potentially serious condition.