Many pregnant individuals anticipate relief from nausea and vomiting after the first trimester. While many experience a reprieve during the middle trimester, the re-emergence of queasiness and an upset stomach during the final stage of pregnancy is a recognized, though often surprising, phenomenon. This late-stage discomfort is typically not a sign of complications, but rather a reflection of the significant anatomical and hormonal shifts occurring as the body prepares for birth. It is important to understand that the symptoms may be similar to those experienced earlier, yet the underlying causes often differ substantially.
The Return of Nausea in Late Pregnancy
For many people, the severe nausea commonly called “morning sickness” subsides as the first trimester ends, often around the 12th to 14th week of gestation. However, a significant minority of pregnant individuals, estimated at 15 to 20%, experience a return of nausea, or even vomiting, in the third trimester, typically beginning after week 28. This renewed discomfort can feel frustrating, but it is a distinct physiological event compared to the hormone-driven nausea of early pregnancy. First-trimester nausea is largely attributed to the rapid surge of hormones like human chorionic gonadotropin (hCG) and estrogen. By contrast, the return of nausea later in pregnancy is primarily linked to mechanical and physical changes within the abdominal cavity.
Factors Contributing to Third Trimester Nausea
The most significant contributor to late-stage digestive discomfort is the sheer size of the growing uterus and fetus. As the baby grows rapidly, the uterus expands to its maximum size, exerting substantial upward pressure on the surrounding organs, particularly the stomach and diaphragm. This physical crowding reduces the stomach’s available capacity, meaning that even a normal-sized meal can lead to a feeling of fullness, distress, and subsequent nausea.
This mechanical pressure also slows the rate of gastric emptying, which is the process by which food leaves the stomach. When food remains in the stomach for an extended period, it increases the likelihood of reflux and indigestion, both of which can manifest as a feeling of nausea. The digestive system is already slowed by the continued presence of pregnancy hormones, which work to relax smooth muscles throughout the body.
Progesterone, in particular, continues to affect the digestive system by relaxing the lower esophageal sphincter (LES), the ring of muscle that acts as a barrier between the esophagus and the stomach. When the LES is relaxed, stomach acid can more easily flow back up into the esophagus, causing the burning sensation known as heartburn or gastroesophageal reflux disease (GERD). The prevalence of GERD-like symptoms jumps from around 26% in the first trimester to over 50% in the third trimester due to this combination of hormonal relaxation and physical compression. This acid reflux is a common cause of nausea in the final months.
Strategies for Symptom Relief
Managing this late-term nausea often involves simple, consistent adjustments to eating and sleeping habits to counteract the physical and hormonal influences. Consuming small, frequent meals throughout the day is highly recommended, as this prevents the stomach from becoming overly full and reduces pressure on the digestive tract. It is beneficial to avoid foods known to aggravate reflux, such as spicy, high-fat, or acidic items, which can further slow digestion and irritate the stomach lining. Fluids should be consumed between meals rather than during them, which helps to prevent overfilling the reduced stomach space.
Positional changes are also helpful, specifically avoiding lying down immediately after eating, giving the stomach contents time to settle. Elevating the head of the bed by propping it up can use gravity to keep stomach acid from backing up into the esophagus during the night. While mild, occasional nausea is often manageable with these lifestyle changes, certain symptoms warrant immediate medical consultation:
- Severe or persistent vomiting that prevents keeping down fluids.
- Significant weight loss.
- Any signs of dehydration.
- New nausea accompanied by severe headaches or blurred vision.
- Sudden, significant swelling, which could be associated with conditions like preeclampsia and require prompt medical evaluation.