Which of the following is the least likely physiological change in pregnancy:
**Core Concept**
Pregnancy is a complex physiological state characterized by various systemic changes to accommodate the growing fetus and prepare the mother's body for childbirth. These changes involve cardiovascular, respiratory, gastrointestinal, and hematological systems.
**Why the Correct Answer is Right**
During pregnancy, there is a significant increase in cardiac output, which is primarily due to an increase in blood volume (40-50%) and heart rate. This helps to meet the increased oxygen and nutrient demands of the fetus. Additionally, there is a decrease in systemic vascular resistance, which is mediated by the production of prostaglandins and other vasodilatory substances. This allows for the increased blood flow to the placenta.
**Why Each Wrong Option is Incorrect**
**Option A:** Increased glomerular filtration rate (GFR) is actually a physiological change in pregnancy. The GFR increases by up to 50% due to the increased blood volume and cardiac output, which helps to excrete waste products and maintain electrolyte balance.
**Option B:** Decreased serum calcium levels are not a typical physiological change in pregnancy. In fact, serum calcium levels often increase during pregnancy due to increased parathyroid hormone secretion and increased calcium absorption from the gut.
**Option C:** Diastolic blood pressure often decreases in the first trimester of pregnancy due to the vasodilatory effects of pregnancy hormones. However, this is not the least likely physiological change in pregnancy.
**Option D:** Decreased respiratory rate is not a typical physiological change in pregnancy. In fact, respiratory rate often increases during pregnancy due to the increased metabolic rate and the need for more oxygen to support the growing fetus.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the physiological changes in pregnancy can be unpredictable and may vary from one individual to another. Regular prenatal care and monitoring are crucial to detecting any abnormal changes and preventing complications.
**Correct Answer:** B. Decreased serum calcium levels.