Morning sickness in pregnancy is most commonly caused by hormonal and metabolic changes early in pregnancy. The leading ideas include:

• Hormonal shifts: Rising levels of hormones such as human chorionic gonadotropin (hCG) and estrogen are associated with nausea and vomiting, especially in the first trimester. In some people, heightened sensitivity to these hormones may trigger more severe symptoms.

• Placental signals: A hormone produced by the placenta and fetus, such as GDF15, is implicated in triggering nausea by acting on the brain’s nausea centers. Individual differences in fetal hormone production and maternal sensitivity help explain why sickness varies in intensity.

• Metabolic factors: Low or unstable blood sugar, changes in carbohydrate metabolism, and fluctuations in blood pressure during early pregnancy may contribute to morning sickness for some women.

• Sensory and environmental triggers: Smells, foods, or fatigue can exacerbate nausea and vomiting in many individuals, even when hormonal causes are present.

Key notes and practical implications:

• Prevalence and course: Morning sickness affects a large majority of pregnant people, often peaking in the first trimester and typically improving by weeks 12–14, though for some it lasts longer. Severe forms (hyperemesis gravidarum) occur in a smaller subset and may require medical care.

• Mild to moderate cases: Often managed with dietary adjustments (snacks like dry crackers, higher-carbohydrate and higher-protein meals), hydration, and avoiding triggers. Prenatal vitamins should be taken as directed, and some people try ginger or other supportive measures. Medication is considered if symptoms are persistent or impairing, with common first-line options including combinations like doxylamine and pyridoxine (vitamin B6).

• When to seek care: If there’s significant weight loss, dehydration, or inability to keep fluids down, or if symptoms are severe and persistent, medical evaluation is important to prevent complications.

If you’d like, I can tailor this into a brief guide with practical tips for managing mild morning sickness or provide sources for deeper reading.