Final answer:
Nausea and vomiting in pregnancy most commonly occur in the first trimester, usually subsiding by about week 12. The second trimester tends to be more comfortable, while the third brings different challenges but less nausea.
Step-by-step explanation:
Nausea and vomiting (N/V) are most commonly associated with the first trimester of pregnancy. This period, which spans from fertilization to the next 12 weeks, often includes symptoms like 'morning sickness,' tenderness around the nipple area, and increased frequency of urination. The morning sickness, which can actually occur at any time of day, is thought to be due to elevated levels of pregnancy-related hormones such as estrogen, progesterone, and hCG, and decreased intestinal peristalsis. Typically by about week 12, the nausea substantially subsides.
In the second trimester, from weeks 13 to 28, most pregnant individuals will feel more energized and experience fewer episodes of nausea. This trimester includes weight gain and the exciting milestone of feeling the fetus's movements.
Conversely, the third trimester includes rapid growth of the uterus and increased weight gain, which can lead to different discomforts such as heartburn, back pain, and frequent urination. However, nausea and vomiting are less common complaints during this time compared to the first trimester.