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 between 8-12 weeks, and usually subsides by week 20 of pregnancy. 1

Timing and Prevalence

Morning sickness, formally known as nausea and vomiting of pregnancy (NVP), affects approximately 30-90% of pregnant women 1. Despite its name, symptoms can occur at any time of day or night 2. For most women:

• Onset: 4-6 weeks of gestation
• Peak intensity: 8-12 weeks of gestation
• Resolution: By approximately 20 weeks of gestation

However, in about 10% of women, symptoms may persist throughout pregnancy and occasionally into the postpartum period 1.

Pathophysiology

The exact cause of morning sickness is not fully understood, but several physiological factors contribute to its development:

• Elevated levels of human chorionic gonadotropin (hCG) and estrogen 1
• Changes in gastrointestinal motility due to progesterone, which can delay gastric emptying 1
• Immunosuppression during pregnancy, which may be part of an adaptive mechanism to protect both mother and embryo from potential foodborne pathogens 3

Severity Spectrum

Morning sickness exists on a spectrum of severity:

• Mild to moderate NVP: Affects 80% of pregnant women 2
• Hyperemesis gravidarum: A severe form affecting 0.3-3% of pregnancies, characterized by:
  • Intractable vomiting
  • Dehydration
  • Weight loss >5% of pre-pregnancy weight
  • Electrolyte imbalances 1

Healthcare providers can assess severity using standardized tools such as the Motherisk Pregnancy-Unique Quantification of Emesis (PUQE) score 1.

Clinical Significance

Morning sickness has several important clinical implications:

• Women who experience morning sickness have significantly lower miscarriage rates than those who don't 3
• Women who vomit have fewer miscarriages than those experiencing nausea alone 3
• Early treatment of nausea and vomiting may prevent progression to hyperemesis gravidarum 1
• Consistent treatment (rather than as-needed) is recommended to maintain adequate fluid and calorie intake 4

Management Considerations

For women experiencing morning sickness, management should be proactive:

1. Diet and lifestyle modifications:

   • Small, frequent, bland meals
   • High-protein, low-fat foods
   • BRAT diet (bananas, rice, applesauce, toast)
   • Avoiding trigger foods and strong odors 1

2. First-line treatments for persistent symptoms:

   • Ginger (250mg capsule 4 times daily)
   • Vitamin B6 (pyridoxine, 10-25mg every 8 hours) 1

3. Pharmacologic options if symptoms persist:

   • Doxylamine (H1-receptor antagonist)
   • Combination of doxylamine and pyridoxine (available in 10mg/10mg and 20mg/20mg formulations) 1

Important Considerations

• Morning sickness is not a normal finding in liver disease, and any elevation in aminotransferases, bilirubin, or bile acids during pregnancy requires investigation 1
• Physical activity may be reduced during periods of morning sickness, which can affect posture and balance 5
• Women with morning sickness may adopt a wider stance for better stability 5

Early recognition and appropriate management of morning sickness can significantly improve quality of life during pregnancy and potentially prevent progression to more severe forms that could impact maternal and fetal outcomes.