Final answer:
The presumptive signs of pregnancy, which might lead a woman to believe she could be pregnant, include amenorrhea, fatigue, nausea/vomiting, and uterine enlargement. These are early signs associated with hormonal changes such as increased levels of estrogen, progesterone, and hCG. Symptoms like morning sickness typically improve by the end of the first trimester, while weight gain and other systemic changes become more evident as the pregnancy progresses.
Step-by-step explanation:
Presumptive Signs of Pregnancy
The presumptive signs of pregnancy are early indicators that a woman might be pregnant. These signs include amenorrhea, which is the absence of menstruation, fatigue, nausea and/or vomiting often referred to as "morning sickness", and uterine enlargement observable as the pregnancy progresses into the second and third trimesters. During the first trimester, other symptoms such as tender nipples, increased appetite, and more frequent urination can also be experienced. The onset of these signs can often be attributed to the dramatic hormonal changes that occur to support the pregnancy, including the increase of estrogen, progesterone, and human chorionic gonadotropin (hCG) levels.
Nausea and vomiting are particularly associated with increased hormone levels and may be exacerbated by heightened sensitivity to odors. Digestive changes, such as decreased intestinal peristalsis, may contribute to these symptoms, which commonly improve by the end of the first trimester. As the pregnancy progresses, additional signs like substantial weight gain become prominent as the fetus grows, and changes in the woman's respiratory and circulatory systems become more pronounced, increasing the blood volume and respiratory minute volume.