CHINA: Research published in BMC Pregnancy and Childbirth concluded a significantly higher prevalence of nausea and vomiting in the Frozen Embryo Transfer (FET) group compared with the stimulated In Vitro Fertilisation (IVF) group.
Nearly 70–80% of pregnant women experience nausea and vomiting, the exact mechanism of which remains unknown. Oestrogen and progesterone may contribute to nausea and vomiting.

According to a study, 26% higher serum levels of oestradiol are found in women with hyperemesis gravidarum. Obese women with higher oestrogen levels experience more severe nausea and vomiting. But these results remain inconsistent. Progesterone causes nausea and vomiting as it reduces smooth muscle contractility, which affects gastric emptying.
In stimulated IVF cycles, oestradiol levels are much higher than those with FET cycles, with oestradiol levels closer to the physiological range. Suppose serum oestradiol level is related to nausea and vomiting during early pregnancy. In that case, women with IVF should experience more nausea and vomiting, but there is a lack of data elucidating this postulate.
Based on the above background, a study was conducted by Evelyn Wong from the Department of Obstetrics and Gynaecology at Queen Mary Hospital from The University of Hong Kong with a team of three researchers, Dr. Jennifer KY Ko, Dr.Raymond HW Li and Dr. Ernest HY Ng compared the prevalence and severity of nausea and vomiting experienced in IVF and FET pregnancies during the first trimester.
The key points of the study are:

360 pregnant women were recruited at six weeks gestation.
The stimulated IVF group had 171 women, and the FET group had 189 women.
The participants filled in the modified Pregnancy-Unique Quantification of Emesis and Nausea (PUQE) to nausea and vomiting weekly till 12 weeks gestation.
The prevalence of nausea and vomiting was the primary outcome measured.
The severity of nausea and vomiting and pregnancy outcomes were the secondary outcomes measured in the study.
The overall return rate was 82.2%, 81.8% in the stimulated IVF, and 82.5% in the FET group.
In the FET group, nausea and vomiting were worse than in the IVF group.
The p-value was 0.032 and 0.046 for weeks 11 and 12, respectively, in the FET group indicating more women felt nauseous or sick in this group.
In the FET group, the duration of nausea was longer in weeks 7 and 8, with a p-value of 0.044 and 0.030, respectively.
During week 6, in the FET group, more women experienced more vomiting in a day with a p-value of 0.042.
Week 8 and 11 had significantly more women with retching or dry heaves in the FET group, with p-values of 0.030 and 0.028, respectively.
As per Multivariate logistic regression analysis, young women experienced more nausea and vomiting during the study period.
The researcher said, "To the best of our knowledge, this is the first prospective study comparing the prevalence and severity of nausea and vomiting between pregnancies from stimulated IVF cycles and FET cycles."
In our study in the FET group, nausea and vomiting were more prevalent compared with the stimulated IVF group, and younger women experience the symptoms more, Dr.Jennifer KY Ko from the Department of Obstetrics and Gynaecology at Queen Mary Hospital said.
The study's strengths were related to the prospective design, which allowed a better interpretation, and women were recruited when they were six weeks pregnant, accounting for more accuracy.
Reference:
Wong, E., Ko, J.K., Li, R.H. et al. Comparison of the prevalence and severity of nausea and vomiting in the first trimester between singleton pregnancies conceived from stimulated in vitro fertilization and frozen embryo transfer cycles. BMC Pregnancy Childbirth 22, 746 (2022).