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 20. 1

Timing and Progression

Morning sickness, formally known as nausea and vomiting of pregnancy (NVP), follows a predictable pattern:

• Initial onset: Symptoms usually begin around 4-6 weeks of gestation 1
• Peak intensity: Most women experience maximum symptoms between 8-12 weeks 1
• Resolution: For most women (approximately 80%), symptoms improve or disappear by around week 20 1, 2
• Persistence: In about 10% of cases, symptoms may persist throughout pregnancy 2

Prevalence and Presentation

• Affects 70-90% of pregnant women 1, 3
• Despite being called "morning sickness," symptoms can occur at any time of day or night 2
• In a prospective study, half of women began experiencing pregnancy symptoms by day 36 after their last menstrual period, and 89% by the end of the eighth week 4

Progression to Hyperemesis Gravidarum

Hyperemesis gravidarum (HG), the severe form of NVP, affects 0.3-3% of pregnant women 1, 2, 3. It is characterized by:

• Intractable nausea and vomiting
• Dehydration
• Weight loss >5% of pre-pregnancy weight
• Electrolyte imbalances

HG usually starts before week 22 of gestation. By week 16, symptoms resolve in >50% of affected persons, and by week 20,80% improve. However, in 10% of cases, symptoms persist throughout pregnancy and occasionally into the postpartum period 1.

Risk Factors and Symptom Onset

Several factors may influence the onset and severity of morning sickness:

• Smoking: Women who smoke tobacco or marijuana tend to have delayed onset of symptoms 4
• Pregnancy viability: Onset of symptoms occurs later in pregnancies that go on to miscarry 4
• Early pregnancy loss: Even in pregnancies lost very early (before 6 weeks), symptoms may be present but substantially reduced 4

Clinical Implications

• Early treatment of NVP may reduce progression to hyperemesis gravidarum 1
• Morning sickness may serve a protective function for the embryo by causing women to avoid potentially harmful foods during the critical period of organogenesis 5
• The timing of symptom onset is important to note as the earliest symptoms begin after key stages of embryogenesis, reinforcing the need for women to initiate healthy behaviors before pregnancy is apparent 4

Management Approach

For women experiencing morning sickness, initial management includes:

1. Diet and lifestyle modifications:

   • Eating small, frequent, bland meals
   • Following the BRAT diet (bananas, rice, applesauce, toast)
   • Consuming high-protein, low-fat meals
   • Identifying and avoiding specific triggers 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 for refractory cases:

   • Doxylamine (alone or in combination with pyridoxine)
   • H1-receptor antagonists (promethazine, dimenhydrinate) 1

Remember that early intervention is key to preventing progression to more severe forms of nausea and vomiting during pregnancy.