When does morning sickness typically start during pregnancy?

When Does Morning Sickness Start in Pregnancy?

Morning sickness typically begins at 4-6 weeks of pregnancy, peaks at 8-12 weeks, and usually subsides by week 20 for most women. 1, 2

Timing and Prevalence

• Nausea and vomiting in pregnancy (NVP) affects 70-90% of pregnant women 2
• Despite being called "morning sickness," symptoms can occur at any time of day or night 3
• For approximately 80% of women, symptoms improve or disappear around week 14, though for some it can last longer 3
• The condition follows a predictable pattern:
  • Initial onset: 4-6 weeks of gestation
  • Peak intensity: 8-12 weeks of gestation
  • Resolution: By week 20 for most women 1, 2

Pathophysiology

Morning sickness is commonly associated with:

• Elevated levels of human chorionic gonadotropin (hCG) 1, 4
• Increased estrogen levels 1
• Changes in gastrointestinal motility 1
• Progesterone effects that can inhibit GI and small bowel motility, leading to delayed gastric emptying 1

Severity Spectrum

Morning sickness exists on a spectrum of severity:

• Mild to moderate NVP (most common): Manageable with lifestyle modifications and possibly mild interventions
• Hyperemesis gravidarum (HG): The severe form affecting 0.3-3% of pregnant women 2
  • Characterized by intractable nausea and vomiting
  • Results in dehydration, weight loss >5% of pre-pregnancy weight, and electrolyte imbalances
  • Usually starts before week 22 of gestation 1, 2
  • By week 16, symptoms resolve in >50% of affected women
  • By week 20,80% improve
  • In 10% of cases, symptoms persist throughout pregnancy 1

Clinical Pearls

• Early recognition and treatment of NVP may help prevent progression to hyperemesis gravidarum 1, 2
• The severity of vomiting during pregnancy can be quantified using scoring systems like the Motherisk Pregnancy Unique Quantification of Emesis score 1
• Although morning sickness is associated with significant discomfort, it has paradoxically been associated with positive pregnancy outcomes in some studies 5

Common Pitfalls

• Dismissing morning sickness as merely an unpleasant but normal part of pregnancy without offering appropriate management strategies
• Treating symptoms only as needed (pro re nata) rather than consistently - this approach is not recommended as symptoms typically continue for weeks or months 6
• Failing to recognize the transition from normal NVP to hyperemesis gravidarum, which requires more aggressive intervention

Morning sickness is a predictable phenomenon with a well-established timeline, typically beginning around 4-6 weeks of pregnancy and resolving by week 20 for most women. Understanding this timeline helps clinicians provide appropriate anticipatory guidance and timely interventions for pregnant women.