Morning sickness condition suffered by Duchess of Cambridge linked to pregnancy complications: research In the study there was a suggestion that hyperemesis in the early stages of pregnancy may be linked to pre-eclampsia but this did not reach statistical significance. The condition is caused by high levels of human chorionic gonadotrophin (hCG), the pregnancy hormone, and a woman's sensitivity to it. It is thought the mechanism behind early hyperemesis is different to that which occurs in the second trimester, when it might indicate problems with placenta's attachment to the womb. This study, which monitored more than one million pregnancies in the Swedish Medical Birth Register between 1997 and 2009, looked at just over 12,000 women who had first admissions to hospital for treatment of hyperemesis gravidarum and the risk associations with later placental dysfunction disorders, compared to women without the condition. There were 10,186 women who were admitted with the condition before 12 weeks and 2,084 who were admitted in the second trimester. Marie Bolin, from the Department of Women's and Children's Health at Uppsala University, and co-author of the study said: "Our study found clear associations in the risk of pre-eclampsia, placental abruption and small for gestational age birth in women presenting with hyperemesis gravidarum, particularly those presenting in the second trimester. The results indicate that pregnancies with hyperemesis gravidarum in the second trimester demand an increased alertness and supervision during the pregnancy for development of any adverse outcomes associated with abnormal placentation. Further research is needed to consider the best treatment and techniques for surveying blood pressure and fetal growth in these high risk women. John Thorp, BJOG Deputy-Editor-in-Chief added: "While the findings of this large study are compelling with strong associations found between hyperemesis gravidarum in the second trimester and placental dysfunction disorders, hyperemesis gravidarum remains a rare condition. As shown in the study, the time of onset of hyperemesis gravidarum influences the risks, therefore women presenting during their first trimester of pregnancy should not be concerned that they will go on to experience adverse complications. Women presenting in the second trimester should be more aware of the risks and consult with their obstetrician for any concerns.