MEDICAL MATTERS: Morning sickness affects between 75 and 85 per cent of women during the first 12 to 14 weeks of pregnancy. In my experience, it is actually a misnomer; many of my patients report sickness throughout the day, with a significant minority experiencing queasiness only in the evening time.
This impression is borne out by the medical literature. Only 17 per cent of women report nausea and vomiting that is confined to the morning. In addition, an unfortunate 13 per cent of pregnant women continue to suffer beyond 20 weeks gestation.
Hyperemesis gravidarum is the term used to describe persistent vomiting that is severe enough to cause a disturbance in fluid and salt balance in the expectant mother. Although it usually requires hospital admission, it is much less common than morning sickness. Hyperemesis affects three in 1,000 pregnant women.
While several possible mechanisms for nausea and vomiting in pregnancy have been put forward, the actual reason and significance of this unpleasant condition remains elusive.
An evolutionary biologist, Dr Samuel Flaxman, of Cornell University in the US, reckons the purpose of morning sickness may be to shield the mother from food-borne illness and to protect the developing foetus against potentially harmful microbes. Flaxman and his colleagues maintain that morning sickness is beneficial rather than harmful to the foetus. Women with nausea and vomiting during pregnancy are less likely to miscarry than women who do not experience it, while normal levels of sickness have never been consistently linked with any negative outcome to pregnancy.
The usually accepted physiological explanation for morning sickness is that it is a response to rising levels of a pregnancy hormone called human chorionic gonadoptrophin. HCG is produced by a healthy placenta, which in turn has led doctors to postulate that morning sickness is a sign of a healthy and well-established pregnancy.
A similar explanation has been put forward by researchers from Stanford University, only in their case they link nausea and vomiting in pregnancy with raised oestrogen concentrations. Doctors Richard Blum and Le Roy Henricks suggest high levels of oestrogen during pregnancy induce a sensitivity or hyperacuity in the part of the nervous system responsible for smell. In other words, the pregnant woman becomes hypersensitive to odours which then induce a sense of nausea. They also mention that morning sickness protects the foetus from miscarriage, since a healthy placenta produces oestrogen during early pregnancy. Research published in the Journal of Obstetrics and Gynaecology in 2000 also supports the healthy placenta/morning sickness link. It found an association between nausea in pregnancy, a larger placenta and a higher birth weight.
If we are to follow the logic of this "morning sickness is good for your baby" logic, the issue of whether to treat the condition or allow women to ride out the queasiness must be addressed. Which brings us to the thorny issue of prescribing in pregnancy.
There is no doubt that the shadow of the thalidomide disaster still hangs over prescribing for any condition in expectant mothers, and especially that of morning sickness. Considered a breakthrough drug at the time, women who took thalidomide (and their offspring) paid a heavy price in the form of major congenital malformations. So what are the physician and their patient to do? Clearly, severe nausea and vomiting must be treated, or else both the mother's and the baby's health may be compromised if hyperemesis becomes established. The treatment of milder symptoms is up to the patient and depends on the level of distress she feels. There are safe drugs, and much can be achieved by slight behavioural modification in the form of how and when the pregnant woman eats.
The main pharmacological plank in relieving symptoms is the use of antihistamines. An analysis of 24 controlled studies into their use found no increase in major malformation in babies over and above the naturally occurring rate of foetal abnormalities. Another recent review in the latest issue of Clinical Evidence found that antihistamines are effective in treating morning sickness, with increased drowsiness being the main side-effect.
Interestingly, it also found one small randomised trial suggesting ginger was effective in reducing nausea in early pregnancy. And a review of some small trials into the use of P6 acupressure - where pressure is applied to an acupuncture point at the wrist by means of a band - suggest that this complementary medical approach may be helpful.
All prescribing in pregnancy must be carried out on a risk: benefit basis. Is there a risk to the baby, and will the mother benefit are the key issues to be teased out. And at the end of the day, it should be the expectant mother who makes the final decision.
Muiris Houston can be contacted at mhouston@irish-times.ie He regrets he cannot answer individual queries