Morning Sickness Timing in Pregnancy
Morning sickness typically begins at 4-6 weeks of pregnancy, peaks at 8-12 weeks (end of first trimester), and resolves by week 20 for most women, placing it predominantly in the first trimester. 1
Timeline of Morning Sickness
Onset and Peak Period
- Symptoms begin at 4-6 weeks of gestation and reach maximum severity between weeks 7-12 of pregnancy 1, 2
- The peak period (8-12 weeks) corresponds to the end of the first trimester, when human chorionic gonadotropin (hCG) levels are highest 3
- This timing coincides with the period of embryonic organogenesis when the developing fetus is most susceptible to chemical disruption 4
Resolution Timeline
- Over 90% of women experience symptom resolution by week 20 (early second trimester) 1, 2
- For most women, symptoms subside completely by the end of the first trimester or early second trimester 1
- The second trimester is typically the "calmest period" with minimal symptoms 5
Extended or Severe Cases
- In 0.3-2% of pregnant women, symptoms progress to hyperemesis gravidarum, a severe form requiring medical intervention 1, 6
- Approximately 10% of women with hyperemesis gravidarum experience symptoms throughout pregnancy and occasionally into the postpartum period 1, 6
- Clinical symptoms are usually more severe during the first trimester compared to later pregnancy 5
Clinical Context for Your Patient
Relevance at 26 Weeks Gestation
For a woman at 26 weeks (well into the second trimester), new-onset or persistent nausea and vomiting would be atypical for standard morning sickness and warrants investigation for alternative causes 5. At this gestational age, consider:
- Pregnancy-specific liver disorders that present in the second or third trimester (such as intrahepatic cholestasis of pregnancy or HELLP syndrome) 5
- Medication-related nausea from seizure or bipolar disorder treatments 5
- Gastrointestinal pathology unrelated to pregnancy 5
Special Considerations with Seizure/Bipolar History
- Women with seizure disorders taking antiepileptic drugs should have been supplemented with 4 mg folic acid daily starting at least one month before conception to reduce neural tube defect risk 5
- Both seizure disorders and their treatments can affect pregnancy outcomes, including increased risk of congenital anomalies 5
- Medication adjustments may be needed during pregnancy, which could contribute to nausea at any gestational age 5
Physiological Basis
Morning sickness correlates with elevated hCG and estrogen levels, which peak in the first trimester 3. The condition is considered an indicator of a healthy pregnancy with adequate hCG production and is associated with lower miscarriage risk 5, 3. Progesterone-mediated delayed gastric emptying also contributes to symptoms 3.