HOW COMMON IS IT?

About 10-20% of women have no nausea or vomiting, 28-30% have nausea 
only, and 52-56% experience some vomiting. 

And among women who report symptoms, there is a huge variation in  
severity.  Many women can still pursue their daily schedules, but 12% 
find ordinary work during pregnancy impossible, and another study 
found that about half of women with symptoms felt their job efficiency 
was reduced.  

WHEN DOES IT START?

Some women experience symptoms within days of conception, but the 
average time from the last menstrual period to the onset of nausea is 
about 5-1/2 weeks.  For many women, a few weeks of nausea will precede 
the onset of vomiting. 

WHEN DOES IT END? 

About 60% of women will be over their nausea by the 12th week from the 
last menstrual period, and more than 90% are feeling better by the 
16th week.  A few unlucky women do have nausea throughout the 
pregnancy, and a few have nausea return in the final weeks of the 
pregnancy. 

IS THE MORNING WORST?

For you?  Only you can answer that.  Yes, it's called "morning 
sickness", but a study found that while there was slightly more 
vomiting from 6-9 a.m., but the rates of nausea were similar 
throughout the daytime hours.  

WILL ALL MY PREGNANCIES BE LIKE THIS?

Well, not necessarily.  In one study, only 63% the women who had been 
pregnant before and had more than 100 hours of nausea said that they 
had similar symptoms.  Every pregnancy is a bit different.  

IS IT REALLY A "GOOD SIGN"?

Several studies have demonstrated that women with no symptoms of 
nausea or vomiting do experience a significantly greater proportion of 
miscarriage.  But most women have live births, so lack of symptoms 
should not be cause for alarm.     

WHAT CAUSES IT?

The simple, safe answer is, "hormones of pregnancy."  Beyond that, 
nobody really knows.  There hasn't been a lot of research.  The 
physiological mechanism isn't anything real obvious, but rather a 
complex interaction.  

Strong correlations have been noted between nausea/vomiting of 
pregnancy and nausea brought on by birth control pills, suggesting a 
common hormonal basis for both phenomenon.  Some researchers found 
higher levels of hCG in patients with nausea and vomiting than those 
who were asymptomatic.   A team of Japanese researchers found 
correlations between the severity of morning sickness and the levels 
of free thyroxine and hCG. 

Please direct any further questions to Colleen Kay Porter, 
cporter@afn.org


SELECTED REFERENCES FOR THIS SECTION:

Roger Gadsby, Anthony M Barnie-Adshead and Carol Jagger, 'A 
prospective study of nausea and vomiting during pregnancy'. Br. J.Gen. 
Pract., 1993, 43: 245-8, p. 246. 

Ann Jarnfelt-Samsoie, G Samsoie, G M Velinder, 'Nausea and Vomiting in 
pregnancyoea contribution to its epidemiology.  Gynecol Obstet Invest, 
1983, 16:221-9.

Masoa Mori, Nobuyoki Amino, Haruo Tamaki, Kiyoshi Miyai and Osamu 
Tanizawa, 'Morning sickness and thyroid function in normal pregnancy', 
Obstet Gynecol, 1988, 72:355-9.

Beverly O'Brien, and Sarah Naber, 'Nausea and vomiting during 
pregnancy: effects on the quality of women's lives', Birth, 1992, 
19:138-43.

Michael R Soules, Claude L Hughes Jr., Jose A Garcia, C H.Livengood, 
Michael R Prystowsky and Eben Alexander, 'Nausea and vomiting of 
pregnancy: role of human chorionic gonadotropin and 17-
hydroxyprogesterone', Obstet Gynecol, 1980, 55:696-700.

Forrest D. Tierson, Caroln L. Olsen and Ernest B. Hook, 'Nausea and 
vomiting of pregnancy and association with pregnancy outcome', Am J 
Obstet Gynecol, 1986, 5:1017-1022.