A client at 9 weeks gestation reports to the nurse that she is experiencing nausea and vomiting in pregnancy. Which pregnancy hormone is thought to cause the nausea and vomiting the client is experiencing in the first trimester of pregnancy?

Choice A rationale Estrogen levels rise significantly during pregnancy to support the uterine lining and fetal development. While elevated estrogen can contribute to a sensitive stomach and altered sense of smell, it is not the primary hormone linked to the rapid onset of morning sickness in the first trimester. It works more globally on tissue growth and vascularity rather than the specific trigger for the chemoreceptor trigger zone that leads to acute nausea. Choice B rationale Human placental lactogen is produced by the placenta and primarily functions as an insulin antagonist. Its main role is to increase the availability of glucose for the developing fetus by altering maternal carbohydrate and lipid metabolism. It does not have a known physiological link to the stimulation of the vomiting center in the brain. It typically reaches peak levels later in pregnancy, whereas morning sickness usually peaks around weeks eight to twelve. Choice C rationale Progesterone is essential for maintaining the pregnancy by relaxing smooth muscles, including the uterus, to prevent premature contractions. This relaxation effect also impacts the gastrointestinal tract, leading to delayed gastric emptying and esophageal reflux. While these factors can cause indigestion or bloating, progesterone is generally considered a secondary contributor to nausea rather than the primary hormonal catalyst that initiates the severe vomiting seen in early gestation. Choice D rationale Human chorionic gonadotropin is secreted by the trophoblastic cells following implantation. This hormone is the hallmark of early pregnancy and its levels double approximately every forty-eight hours during the first trimester. High concentrations of this hormone are strongly correlated with the severity of nausea and vomiting because it directly stimulates the emetic center. Levels typically peak around ten weeks and then decline, matching the clinical course of most morning sickness cases.