The Duchess of Cambridge, who is pregnant with her third child, had to cancel a number of engagements during all three of her pregnancies due to severe morning sickness.
Now researchers have established a link between the ‘old wives’ tale that morning sickness may indicate a healthy pregnancy and the reason smoking is so detrimental.
Their paper, published in the Journal of Molecular Endocrinology, discusses the importance of the hormone endokinin for healthy pregnancies, its role in causing morning sickness, and how its normal function may be adversely affected by smoking, leading to poor outcomes in pregnancy.
Successful and effective implantation of the placenta is essential for a healthy pregnancy, but scientists say that how that is achieved remains to be firmly established.
The role of peptide hormones and the placenta in causing morning sickness, in particular, is unclear.
Professor Philip Lowry and Dr Russell Woods, of Reading University, reviewed the critical roles that peptide hormones have in ensuring successful implantation of the placenta.
They also discussed how endokinin can indirectly lead to the development of morning sickness symptoms, and how its normal hormone function can be impaired by smoking.
Endokinin is a peptide hormone found throughout the body that can affect blood supply to organs locally.
Placental endokinin, even at low levels, appears to be capable of improving local blood flow, which is a key factor for ensuring successful implantation.
Endokinin also acts on the brain to induce nausea and vomiting.
The researchers said thar is why drugs that block the actions of endokinin in the brain are often used to treat nausea associated with chemotherapy. And recent findings indicate that tobacco smoke also influences lung endokinin levels.
Since hormones such as endokinin are transported in the blood, they can also affect functions in other parts of the body and this is the basis of the link between morning sickness, pregnancy and smoking.
Increases in endokinin levels during pregnancy that ensure good placental blood flow can also overspill and activate the brain areas that cause morning sickness symptoms.
Similarly, the nausea experienced by non-smokers on inhaling tobacco smoke may be due to raised levels of endokinin in the lungs also activating those brain areas.
Given that smoking during pregnancy is known to lead to poor placental implantation, Prof Lowry said that suggests that impaired endokinin activity may be involved.
He said: “It is feasible that the regular release of lung endokinin into a mother’s blood from smoking adversely affects the normal local response to placental endokinin, which is needed to ensure a healthy pregnancy.”
But he warned: “There may be a temptation to use endokinin blocking drugs to treat morning sickness during pregnancy, but these findings suggest that such drugs could affect the health of the pregnancy and must be avoided.
”Professor Lowry added: “I hope that this article will give some psychological relief to pregnant women suffering from morning sickness, but will also persuade smokers who are intending to have a baby to kick the habit well beforehand.”