When does morning sickness typically start during pregnancy?

Morning Sickness Onset During Pregnancy

Morning sickness typically begins at 4-6 weeks of pregnancy, peaks at 8-12 weeks, and usually subsides by week 14 for approximately 80% of women. 1

Timeline of Morning Sickness

• Initial onset: 4-6 weeks of pregnancy 1
• Peak intensity: 8-12 weeks of pregnancy 1
• Resolution: By week 14 for about 80% of women, though for some it can last longer 1, 2
• Complete resolution: Usually by week 20 for most women 1

Despite the common name "morning sickness," symptoms can occur at any time of the day or night 2. Research shows there is typically a peak probability of nausea in the morning, a sustained probability throughout the day, and a slight peak again in the evening 3.

Pathophysiology

Morning sickness is associated with several physiological changes during pregnancy:

• Elevated levels of human chorionic gonadotropin (hCG) 1, 4
• Increased estrogen levels 1
• Changes in gastrointestinal motility 1
• Progesterone effects that 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 nausea and vomiting of pregnancy (NVP): Most common form, affecting up to 80% of pregnant women 1, 2
• Hyperemesis gravidarum (HG): The severe form affecting 0.3-3% of pregnant women 1, 2
  • Characterized by intractable nausea and vomiting, dehydration, weight loss, and electrolyte imbalances
  • Usually starts before week 22 of gestation
  • Symptoms resolve in >50% of affected women by week 16, and 80% by week 20
  • In 10% of cases, symptoms persist throughout pregnancy 1

Important Clinical Considerations

• Early recognition and treatment may help prevent progression to hyperemesis gravidarum 1
• Symptoms should be treated consistently rather than only when they emerge (pro re nata), to ensure adequate fluid and calorie intake 5
• Two-thirds of women will experience similar symptoms in successive pregnancies 6
• The condition has significant impact, with an estimated 8.5 million working days lost per year due to pregnancy nausea and vomiting 6

Common Pitfalls

1. Terminology misconception: Referring to this condition simply as "morning sickness" is inaccurate and can trivialize the experience, as symptoms occur throughout the day 3
2. Delayed treatment: Waiting until symptoms are severe before initiating treatment may lead to unnecessary suffering and potential progression to hyperemesis gravidarum 1, 5
3. Inconsistent management: Treating symptoms only when they emerge rather than consistently can lead to inadequate nutrition and hydration 5