Morning sickness (or really 'all day and all night sickness'), is one of the most common physical signs of early pregnancy. However, not all women will experience morning sickness and it is not an 'essential' physical sign you have to experience to be pregnant.
Typically, morning sickness starts around 6 weeks of the pregnancy (or about 2 weeks after the period was due) and continues until about 12 to 14 weeks of the pregnancy. However, morning sickness may start later than 6 weeks and may continue until 16 to 20 weeks of the pregnancy (and occasionally beyond).
Morning sickness may make you feel constantly nauseous, or bring on 'waves' of nausea at different times of the day. Some women will occasionally (or regularly) vomit and a few will vomit excessively to the point of becoming dehydrated or produce more saliva, known as 'ptyalism' (pronounced 'tie-al-ism'). The nausea can change your eating habits for a while and some women will not gain weight initially (or even lose weight for a few weeks) because of their morning sickness. This is normal and your baby will rely on your body's fat stores to grow. Usually when the nausea and/or vomiting settles, your appetite returns and you experience a 'growth spurt' as your body 'catches up'.
Why does morning sickness occur?
We don't really know exactly why 'morning sickness' occurs or why some women suffer from it more than others. The most common reason given is the hormonal changes of early pregnancy and a woman's individual response to this. However, it is not unusual for morning sickness to worsen during times of emotional stress (particularly in the later months of pregnancy) and many pregnant women will vomit 'out of the blue' without warning, either as a reaction to a certain smell or something like accidentally pushing the toothbrush too far down the back of their throat!
The following are the most likely theories behind the possible causes of morning sickness:
The pregnancy hormone 'HCG'
During the first 12 weeks of pregnancy the developing baby produces a hormone called 'Human Chorionic Gonadotrophin' (or 'HCG'). HCG starts to be released into the woman's blood stream soon after her baby implants into the lining of her uterus (about 8 to 12 days after conception, or just before the next period is due). The HCG blood level initially starts off very low (at least 5 IU/L), but then rapidly increases (doubling every 2 to 3 days) so that within several days to a week or more, it becomes high enough to be detected in the woman's urine (at least 50 to 80 IU/L). Once this level is achieved, a urine pregnancy test will show as being 'positive'.
The HCG hormone peaks to its highest levels between 8 and 11 weeks of the pregnancy. Then the level slowly decreases, lowering at 12 weeks and again at about 16 weeks of the pregnancy. The HCG level remains lower until several weeks after the birth of the baby. As the HCG levels lower, the maturing placenta takes over the role of producing other hormones to support the pregnancy (at around 12 weeks). Higher than average HCG levels may indicate a multiple pregnancy. This is why women carrying twins or triplets or more can experience more severe morning sickness.
Low blood sugar levels
Many women who experience morning sickness often find that by eating something their nausea improves or goes away. Low blood sugar levels can produce nausea and may result from a lack of food and energy. During early pregnancy, a woman's metabolism increases by up to 20%. This means that her body burns through the food she eats more rapidly. The 'low blood sugar theory' may explain why many pregnant women feel worse in the mornings (because they haven't eaten all night) and why a small, plain snack will usually make them feel better.
Women with morning sickness usually describe only being able to tolerate certain foods at this time. It is not unusual to hear stories of women surviving on little more than vegemite and toast or baked beans during their early weeks of their pregnancy! This changes back to 'normal' as the nausea subsides and you should be able to return to having a more balanced diet.
Changes to smell and taste
During pregnancy many women find that their sense of smell and taste are acutely sensitive. Odours and aromas that may have previously been tolerable or enjoyable can now make you heave, literally! While these do not generally cause morning sickness, they are certainly capable of making it worse.
Stress and anxiety
Pregnancy can be a stressful time for all involved. Early pregnancy is often accompanied by feelings of ambivalence about having a new baby and what that will mean to your life, career, relationships, finances and other children (if you have them). While stress and anxiety may not actually cause morning sickness, they can contribute to its intensity and perhaps make the sickness continue beyond 16 weeks (and possibly see its return during later pregnancy). Some women will seek homoeopathic remedies for this. You can read more in nausea and vomiting during late pregnancy.
Emotional stress may be an ongoing issue if the woman has concerns, fears and anxiety about the pregnancy itself. This may stem from simply not enjoying the pregnancy process, or from a past experience of miscarriage or stillbirth. Waiting for the results of genetic tests can also bring weeks of continuous stress or if your caregiver questions the health of you or your baby.
Persistent emotional stress can often be accompanied by nausea and maybe even vomiting. This can make the situation even more difficult to deal with. The nausea may continue until after the pregnancy progresses beyond a certain point in time, or even until your baby is born. Sharing your fears with others you trust, or seeking professional advice may be helpful at this time.
Related pregnancy articles:
Last revised: Friday, 7 March 2014
This article contains general information only and is not intended to replace advice from a qualified health professional.